‘i ree ted smth ae 4 ; ; Ay ee Copyright N° COPYRIGHT DEPOSER Bi ve V4 “ih ve Y ie i The Rural Manuals Epitep sy L. H. BAILEY MANUAL OF TREE DISEASES The Rural Manuals Epitep By L. H. BAILEY * MANvuAL oF GARDENING — Bailey Manuat or Farm Animats — Harper FARM AND GARDEN Ru e-book — Bailey MANvAL OF Fruit Insects — Slingerland and Crosby ManvuAu or WEEDs — Georgia THe Pruninc-MAanuat — Bailey Manuat or Fruit Diseases — Hesler and Whetzel Manuva or Mitk Propvucts — Stocking MANUAL OF VEGETABLE-GARDEN InsEcTs — Crosby and Leonard MaANvuAL oF TREE DisEAses — Rankin ManvuAt or Home-Maxine —Van Rensselaer, Rose, and Canon MANUAL OF TREE DISEASES BY We HOW AnD RAEN KEN: A.B:; Pa.D. ASSISTANT PROFESSOR OF PLANT PATHOLOGY NEW YORK STATE COLLEGE OF AGRICULTURE AT CORNELL UNIVERSITY Neto Bork THE MACMILLAN COMPANY 1918 All rights reserved | fe iy 0 , : ng | ; ed) oi ‘ % aA - bs ¥ Copyrigut, 1918, By THE MACMILLAN COMPANY. ? Set up and electrotyped. Published November, 1918. © ‘ e¢ © i site hes oc a0 Norwood jsress J. S. Cushing Co. — Berwick & Smith Co. j Norwood, Mass., U.S.A. ©cias0s205 . ie be PREFACE THE steadily accumulating knowledge of the diseases of trees in the United States has never been brought together and made available to the general public. The intention of this Manual is to describe and suggest means of control for the tree diseases that have been most studied. Much remains to be learned about many of these diseases, and still many more have never been investigated. Therefore, in the treatment of this subject there are many unavoidable limitations which the trained reader will perceive. The diseases of fruit-trees, and of field and vegetable crops, have received the attention of plant pathologists in most parts of the country for many years. The results of these investigations have been made available to the growers of these crops in various ways. On the other hand, the diseases of forest, shade, and ornamental trees have been largely neglected until very recently. Tree diseases cause enormous losses in the large tracts of forests on which we depend for timber. The timber owner has been slow to adopt the fundamentals of scientific forest practice, and so far methods for the control of forest-tree diseases have not begun to operate in reducing losses. The owners of shade and ornamental trees are constantly con- fronted with diseases which they wish to control. They have become accustomed to controlling insects, but the funda- mentals involved in the appearance of a disease and the meas- ures necessary to protect trees from further damage are largely puzzling to them. An understanding of the cause of disease is essential to the undertaking of adequate control measures. That the tree is Vv vi PREFACE a living organism which requires water, food, air and sunlight is often overlooked. Many of the diseases outside the forest are due to the failure to recognize the importance of main- taining suitable conditions for tree growth. The soil must contain the proper supply of food materials, and be of a texture which will conserve the water and air that are necessary for healthy root development. Pavements and sod are frequently never considered as the cause of the decline and death of trees. Likewise, it is seldom appreciated that the smoke and poisonous gases in the atmosphere in cities kill many trees. Also the appearance of leaf-spots, cankers, wood-rots and root-rots in no way explain themselves unless it is understood that in- visible parasitic plants are growing in the living tissues of the tree and causing their death. The technical facts regarding the relation between a tree and its environment are more easily comprehended than the life history of the parasites which cause diseases. Nevertheless, the tree owner must understand the nature of these organisms, the appearance of the symptoms they produce, and many other facts regarding diseases before he can intelligently attempt their control. It is hoped that the details concerning the diseases discussed in this book will assist to that end. The treatment has been made as simple as possible, and only the essentials regarding the disease, which are necessary to recognize and understand it, have been in- cluded. A glossary is appended, which will assist in explain- ing the more technical terms. It has been necessary to treat the general and specific diseases separately. Those diseases which are more or less common to all kinds of trees are discussed in the first four chapters. The more specific diseases will be found in the chapters follow- ing, which are arranged alphabetically according to the com- mon name of the various groups of trees. Cross-reference has been freely made in the different chapters to more complete discussions found elsewhere. This would be unnecessary if PREFACE Vil the book were to be read from cover to cover. The plan of the book is intended, however, to facilitate the diagnosis of a dis- ease of a certain kind of tree and to group the diseases of this tree in one place where comparisons may be made. Under each of the host-chapters, the diseases are arranged according to the part of the tree affected and will be found in the fol- lowing order: leaf, twig, branch, trunk and root diseases. The reader is advised to make free use of the index, which will facilitate the finding of those discussions unavoidably scattered. It is regretted that specific information is not yet available on many common tree diseases. Most of the leaf-spot diseases have not been studied. Likewise, control measures are largely limited to eradication methods, so far as definite reeommenda- tions can be made. This apparently will always be the case for the diseases of the woody parts of trees, until means of naturally or artificially immunizing trees are devised. Spray- ing and dusting for leaf diseases will be practicable when these diseases are better understood. Such methods are expensive, however, and their use will be limited for this reason. The author is indebted to Dr. F. D. Kern, who has read the discussions of the rust diseases and offered many helpful suggestions. Grateful acknowledgment is also made to Mrs. W. H. Rankin and to the following co-workers in the Department of Plant Pathology at Cornell University for many suggestions regarding the manuscript and for photographs loaned: Prof. H. H. Whetzel, Dr. L. R. Hesler, Dr. Donald Reddick, Dr. V. B. Stewart, Dr. C. T. Gregory, Dr. H. M. Fitzpatrick, and Miss Edwina Smiley. W. Howarp RankIN. CorNELL UNtIversity, ITHaca, New YorRK, September 1, 1918. CONTENTS CHAPTER I SEEDLING DISEASES AND INJURIES . Damping-off Sun-scorch Winter-drying Freezing-to-death Smothering-disease CHAPTER II LEAF DISEASES AND INJURIES Winter-drying Late frost-injury ; , Drought-injury and sun-scorch . Smoke- and gas-injury Leaf-spots Powdery mildews Leaf-cast of conifers . Sooty molds Silver-leaf . CHAPTER III Bopy AND BRANCH DISEASES AND INJURIES . Freezing-to-death of twigs and bark . Frost-cracks ~ 3 é Sun-seald . , Lichen-injury Slime-flux . Mistletoe diseases Electrical injuries 1x 99 Www bt Hm “J Co L 106) ee ae aS Cr Or Or wowWwon co on on on ¢ = oo or) i=) CONTENTS Galls Wood-rots CHAPTER IV Root DIsEASES AND INJURIES Drying and drowning Freezing-to-death Gas-injury . Shoe-string root-rot Mycorhizas Roots parasitized by dowenae plants, CHAPTER V ALDER DISEASES Powdery mildew of catkins Catkin-deformation Brown checked wood-rot Common white wood-rot Root-tubercles CHAPTER VI ARBOR-VITZ DISEASES Seedling-blight . Leaf-blight Brown pocket heartwood- mot Red-brown root- and butt-rot CHAPTER VII AsH DISEASES . Leaf- and twig-rust White heartwood-rot CHAPTER VIII Batp Cypress DISEASES Pecky heartwood-rot 97 OF CONTENTS CHAPTER IX Basswoop DISEASES Powdery mildew Leaf-spot White sapwood-rot Southern root-rot CHAPTER X BeecH DISEASES Yellowish sapwood-rot Common white wood-rot Uniform white sapwood-rot White butt-rot . Parasitized roots CHAPTER XI Brircw DISEASES Leaf rust Yellow jeaf blister Red leaf-blister . Powdery sapwood-rot Yellowish sapwood-rot Common white wood-rot Brown heartwood-rot White butt-rot . CHAPTER XII BucKEYE DISEASES Leaf-blotch Powdery mildew Curled leaf-blight and wieches’ aroaw White sapwood-rot CHAPTER XIII Butternut DISEASES Leaf-spot Xl CONTENTS Common white wood-rot Brown checked wood-rot CHAPTER XIV CATALPA DISEASES Yellowish wood-rot Brown butt-rot . CHAPTER XV CrepAR DISEASES Eastern leaf-rust Western leaf-rust Brown felt-blight Eastern witches’-broom Western twig-blight and relion feroemt Branch-swellings Pecky heartwood-rot CHAPTER XVI CHESTNUT DISEASES Large leaf-spot . Twig-blight Endothia canker Strumella canker Brown checked wood-rot Straw-colored heartwood-rot White piped butt-rot CHAPTER XVII Eum DISEASES Leaf-spot Powdery mildews Brown wood-rot CHAPTER XVIII Fir DISEASES . Leaf blister-rusts CONTENTS Leaf-rusts . Leaf-cast 3 Rust witches’-broom . Gray mold twig-blight Mistletoe burl and witches’-broom Pecky wood-rot . Red-brown sapwood-rot Stringy red-brown heartwood-rot Brown pocket heartwood-rot Brown heartwood-rot Brown root- and butt-rot . Red-brown root- and butt-rot Yellow root-rot . CHAPTER XIX HacKBeRRY DISEASES Powdery mildews Witches’-broom CHAPTER XX Hemuock DISEASES Seedling root-rot Leaf-blight Brown-mold leaf Blipht Leaf and cone blister-rusts Leaf-, cone- and twig-rusts Red-brown sapwood-rot Stringy red-brown heartwood-rot Brown pocket heartwood-rot Cuboidal wood-rot : Red-brown root- and butt-rot s CHAPTER XXI Hickory DISEASES . Leaf-mildew and witches’ Sere Common white wood-rot X1V CONTENTS CHAPTER XXII PAGE JUNIPER DISEASES . : : ‘ : : : 5 . 190 Seedling twig-blight . 4 ‘ : : : ; ‘ - 190 Leaf- and stem-rusts (general) . : . i ‘i : . 192 Leaf- and twig-rusts . ‘ : ; ‘ : ; : . 196 Cedar-apples. : : : ‘ ; P : ‘ . 197 Rust witches’-brooms : : : : ; : , « 200 Branch-galls.. : : s : ; ; ; » 200 Fusiform branch-sw alah : ‘ ; ; : 2 . 202 White bark : : : ; : ‘ ‘ , . 204 Brown pocket heartw Sadao : : : : : 5 . 204 White pocket heartwood-rot : : : ; F - 206 Yellow wood-rot ; ; : F en : : » 208 Stringy brown wood-rot. : ‘ $ ‘ ‘ : . 209 Basal heartwood-rot . ; : ; é : : ; « 210 CHAPTER XXIII LarcH DISEASES. : : 5 : : ‘ ; , pees Seedling root-rot : : : , c : ; : - 22 Leaf-rusts . : , j ‘ , . 212 Mistletoe burl and witches Riraorn F ; = ; ‘ . 214 Pecky wood-rot ‘ ; F : : : : : « 2S Red-brown sapwood-rot . : : F : é é Ae alls Brown heartwood-rot ; , : : é : : +) 2G Brown pocket heartwood-rot 2 : . ‘ ; oe Red-brown root- and butt-rot . : ‘ ‘ Z < oro eles Yellow root-rot . ‘ : : ; ; , : , « 218 CHAPTER XXIV Locust DISEASES . : : ‘ é ‘ : : : . 1219 Yellow wood-rot : : ; 5 : : : é « “219 Brown checked wood-rot . ; : ; : F ‘ 2 22 Root-tubercles . 4 . , 3 ‘ : ; ‘ . 22 CHAPTER XXV Marie DISEASES. ‘ : , : : : : : : 1228 Tar leaf-spot . : : ‘ ; : 4 : : . | 223 CONTENTS XV PAGE Black-specked was 225 Leaf-spots . 226 Powdery mildews 227. Leaf-blight 228 Canker 229 Wilt . 3 231 Common white youdtot 232 Brown checked wood-rot 232 White strand wood-rot 233 Uniform white sapwood-rot 234 White streaked sapwood-rot Dow White butt-rot . : : : 236 CHAPTER XXVI Oak DISEASES . , ; : : : : ; ; ; Ae PBI Leaf-blight : : ; : : ? : ; : Bay Leaf-blister : : ; . : : ; , : 3239 Powdery mildews : ‘ : : : : 5 : . 2AT Brown mildew . : . : F ; . : 2 5 PAS Large leaf-spot . : : : : : : ; ji . 248 Twig-blight ; ‘ ‘ 3 ; F é : : . 244 Strumella canker ‘ : 3 , : ? : : » 245 Brown checked wood-rot . s : : : : ; 5 ii Common white wood-rot . : : P : : : 5 PRO White pocket heartwood-rot —. ‘ : ; ‘ : . 250 String and ray butt-rot. ‘ ‘ ; : : ; 2 252 Wet heartwood-rot . : ? : : . : : 5 a! Honeycomb heartwood-rot , : ; , : ‘ 200 Soft heartwood-rot . ; x F : 3 ; : 5 ARI White piped butt-rot . ‘ ‘ ; i : ‘ : > (258 Straw-colored butt-rot ‘ ; : ; : é i . 259 White wood-rot . : : 5 : ; : : E . 260 White butt-rot . : : : ; : : : A -- 260 White root-rot .. . ‘ : : ‘ : : f Le oll CHAPTER XXVII PINE DISEASES : : - : , 5 ‘ : : . 264 Seedling root-rot ‘ ; : 2 ‘ : ; 3 . 264 Xvi CONTENTS PACE Leaf blister-rusts 5 ; : : ; ‘ A : . 265 Leaf-rust . ; , ‘ 5 " : < 3 « 200 Leaf-cast of white pine’. ; : : : : ; . 270 Brown felt-blight f : : : ee! Leaf-cast and witches’-broom ae Sei vellone pine : : aad Twig-blight : : : : : F ‘ . 2h2 Mistletoe burls and witches: ireama : : : F «2273 Blister-rust of five-needle pines . : ‘ : i . ~ QA Sweet-fern rust . : : ; E : F : ; 28 Comandra*¥ust . ; : : 3 ; ; i : ne Sie Castillejasrust . : ; . , 2 : ‘ é . 285 Oak rust . ‘ : : ; : : : ; : . S2RF Pinon blister-rust ; : : : ‘ : : ; . 290 Basal canker. , é : : : é d : ; 290 Pecky wood-rot : : : : oy MY oe : ‘ . 291 Red-brown sapwood-rot . : : : ; : ‘ . 292 Brown heartwood-rot é ; ; 5 : , 2 » 292 Brown pocket heartwood-rot . ‘ , ‘ ‘ 5 . 293 Red-ray wood-rot : ‘ ; i 5 : ‘ . 293 Red-brown root- and butt-rot . j : ; : ; . 294 Yellow root-rot . : - : ; ; : i ; . 296 Brown root- and butt-rot . : : : : : : . 296 CHAPTER XXVIII PopLarR DISEASES . ‘ ; : ; : P ‘ : . 298 Leaf-rusts . ‘ ; ‘ : : : : : : . 298 Powdery mildew : : : A 4 : : : . 300 Yellow leaf-blister . : : ; : : rc 4 UU) Catkin-deformation . : : ; : : : 5 5 lil Canker : : 5 : : : : : ; $ . oul Limb-gall . : 3 : : 5 : : ; : . 3804 Common white wood-rot . : 2 - : : 2 . 304 White pocket heartwood-rot ‘ : . ; : . 310 White butt-rot . 3 : : : : ; : é Se asi; CHAPTER XXIX SPRUCE DISEASES . : : 4 : 5 : : ‘ 5 ells: Seedling twig-blight . - : : = - : : . 313 CONTENTS Leaf blister-rusts Leaf-rust Brown felt- blight Leaf- and twig-blight Cone-rust . Rust witches’ Berane. Mistletoe witches’-broom . Pecky wood-rot Red-brown sapwood-rot Stringy red-brown heartwood-rot Brown pocket heartwood-rot Cuboidal wood-rot Brown root- and butt-rot . Red-brown root- and butt-rot Yellow root-rot . CHAPTER XXX SYCAMORE OR PLANE TREE DISEASES Leaf- and twig-blight CHAPTER XXXI WALNUT DISEASES Leaf-spot Common white wood- 16 Brown checked wood-rot CHAPTER XXXII WILLow DISEASES Powdery mildews Leaf-rusts . Tar leaf-spot Common white wood-rot White wood-rot CHAPTER XXXIII TREE SURGERY Pruning cc COO mI Wo Ww WO & & OO Ww WWNNNNND SESE cS — wo Oo (5%) XVili CONTENTS Disinfecting wounds . Wound dressings Lesion excision . Cavity treatments CHAPTER XXXIV SPRAYING AND DusTING FoR LEAF DISEASES APPENDIX Common names of trees Synonymy of polypore names Glossary . : A : : : General bibliography of tree diseases . INDEX PAGE 348 048 ool 300 307 361 361 364 365 367 ovl SR OO, Se Stee ea ILLUSTRATIONS Frost-crack in a maple Frost-crack healed over in summer Mistletoe growing on white fir Galls on branch of oak Polypore fruiting-body showing : spores Shoe-string root-rot on pine Young toadstools of Armillaria mailed Mature fruiting-body of see root-rot fungus . Ash rust Leaf-spot of basew oad (by V. iB. Stew A . Fruiting-body of Fomes fomentarius ; . Beech wood decayed by Fomes applanatus . Fruiting-body of Polyporus betulinus . Leaf-blotch of horse chestnut . Leaf-spot of butternut . Brown felt-blight . Endothia canker of chesiane . Mycelial fans between bark and w a . Spore-horns of chestnut canker fungus . Perithecial stage of chestnut canker fungus . Leaf-spot of elm (by H. M. Fitzpatrick) . Powdery mildew of elm ; 3. Pecky wood-rot, early stage . Pecky wood-rot in Douglas fir : . Fruiting-body of Echinodontium tinctorium . Brown heartwood-rot of Douglas fir . . Fruiting-bodies of Rhizina undulata (after Bupa . Cuboidal wood-rot of hemlock (by G. F. Atkinson) . Cedar-apple fungus on wild apple leaves (after Weimer) Cedar-apple fungus on haw leaf . Cedar-apples. — early stages of development (after Wecimen) 2. Cedar-apples in late autumn (after Weimer) . Cedar-apple in spring with spore-horns (after Weiner) X1x PAGE 50 50 56 63 68 79 80 81 94 102 106 109 114 119 125 131 142 143 145 146 12 153 164 164 167 169 178 186 194 195 197 197 198 ILLUSTRATIONS . Fruiting-bodies of Fomes roseus 5. Fruiting-body of Fomes rimosus Tar leaf-spot of maple . Leaf-spot of maple caused by Piyllosticala minima Leaf-spot of maple caused by Glaosporiwm apocr as m pues: H. M. Fitzpatrick) , ; Leaf-blight of maple . . Nectria canker on maple i . Sections through Nectria canker on mane . Sections through trunk of maple affected by wilt 3. Section through fruiting-body of Hydnum septentrionale . Leaf-blight of oak tx. 5. Leaf-blister of oak (by H. H. Whetzel) . Powdery mildew on oak leaf (by G. F. Ailaneen) . Twig-canker on oak : . Brown checked wood-rot in oak as G. iH Adlaneoni . Fruiting-bodies of Polyporus sulphureus : . Fruiting-body of Polyporus Berkeleyi . Fruiting-body of Polyporus dr yadeus 2. Blister-rust on twig of white pine (after Hele aaa Whetzel) Blister-rust on trunk of white pine . Uredinial stage of Cronartiwm ribicola on currant Gites Hester aa Whetzel) 5. Telial stage of Cronartium ribicales on veureent (alter Headee Pa Whetzel) Blister-rust on lodgepole pine . Limb-galls on poplar Common white wood-rot (after Ejeaior ea Whetsel) 9. Fruiting-body of Fomes igniarius Fruiting-body of Fomes igniarius (form éalled Fores iigeieree . Section through fruiting-body of Fomes igniarius 2. Witches’-broom on black spruce 3. Mistletoe witches’-brooms on black spruce . Pecky wood-rot in spruce . 5. Pecky wood-rot, advanced stage . Leaf-blight of syeamore . Sycamore tree defoliated by eae iis te fangs (a M. F. Barks) . Cankers on small sycamore twigs : F . Cankers on limbs of sycamore . Powdery mildew on willow leaves &, G. F. Dy eigea PAGE 205 220 224 226 227 228 229 230 231 235 238 239 242 244 248 249 253 262 276 277 278 278 286 304 306 307 308 309 322 323 325 326 J04 325 336 307 342 MANUAL OF TREE DISEASES MANUAL OF TREE DISEASES CHAPTER I SEEDLING DISEASES AND INJURIES From the very beginning of the life of a tree, the seedling is subject to many more or less serious diseases. Damping-off may cause death, even before the tiny plant has grown above the surface of the soil. Later, if damping-off is avoided, va- rious blights are common in the seed- and transplant-bed. Although many pathogenes are known to cause seedling dis- eases, it is very difficult for the layman to identify the trouble any more accurately than by the general symptoms of damping- off or blight. Damping-off symptoms are mostly due to the activities of specific soil-harbored fungi. Blight symptoms may be produced by various rapidly spreading fungi, or by adverse moisture and temperature conditions. After a careful comparison of the blight symptoms produced by environmental conditions, with the usual symptoms caused by parasites, the layman should be able to distinguish between these two general types of seedling blights. In some cases, the seedlings of certain kinds of trees are affected by well-known specific leaf-, stem- or root-parasites which cause blight. These dis- eases are described in the chapter on the diseases of the species of tree affected. Otherwise, the damping-off and blights such as sun-scorch, winter-drying and freezing-to-death of seedlings of both coniferous and deciduous trees, are treated below. B 1 2 MANUAL OF TREE DISEASES DampINnG-OFrr Caused by various species of fungi The damping-off diseases have commanded serious atten- tion from all persons who have attempted to grow seedlings, especially of conifers. Schreger, in an early compilation of the facts known about tree diseases, published in 1795, writes about the damping-off of beech seedlings. Since the growing of large quantities of seedlings for forest planting was first attempted in Europe, the earlier literature on damping-off appeared mostly in foreign languages. American nurserymen have grown small quantities for ornamental and shade tree stock for many years. The increasing demands for large quantities for forest planting were not supplied, however, by the production of the commer- cial nurserymen. It is thought that the small quantity pro- duced and high prices demanded for the stock were due mainly to the difficulties of handling the damping-off diseases. To-day the growing of coniferous seedlings in federal and state nurseries has developed until millions of trees are produced yearly. It was during the development of these specialized nurseries that the damping-off diseases in this country were studied, and methods evolved for their control. Damping-off is a universal seedling trouble. The fungi causing the disease are common soil-harbored organisms asso- ciated with decaying plant material. Seedlings grown in new soil may suffer from damping-off as severely as those in beds which produced diseased plants the previous year. The seed- lings of coniferous trees in general show marked susceptibility, while those of deciduous trees are less often attacked. Beech and maple seedlings, however, often suffer. When no pre- cautions are taken, damping-off may kill practically the entire stand of seedlings, especially when large numbers are grown under crowded conditions. SEEDLING DISEASES AND INJURIES 3 Symptoms. The critical period in the development of tree seedlings, so far as damping-off is concerned, extends from the time of the germination of the seed until the stem-tissues become woody, —a period of one or two months. Usually the first indication of damping-off is a water-soaked or brown area of decaying tissue in the stem, near the surface of the ground. If the dis- ease occurs very early in the development of the plants, the stems may be killed before their tips emerge from the ground. Often, also, the lesion originates just below the surface of the soil after the plant has pushed out, and wilting of the plant is the first sign of the trouble. Wherever the lesion may occur, the diseased stem-tissue soon collapses and allows the plant to fall over, while further disintegration of the tissue results in the death of the seedling. Root-rot may accompany damping- off and often is only another indication of the work of the same fungus. In the case of deciduous trees, especially the beech, the first lesions may show as cotyledon-spots. These lesions soon enlarge, however, so that the stem is involved and damping- off follows. Under conditions favorable for the development of damping-off fungi, large circular areas of dead plants appear and only a few days are sufficient for the spread of the patho- gene from a few centers to all parts of the seed-bed. Cause of damping-off. Numerous species of fungi have been found to cause damp- ing-off. In general these fungi have no restricted host-range, and are so prevalent and omnivorous that seedling crops uni- versally suffer. In this country most of the work on these diseases has been done with conifers. Numerous species and forms of fungi belonging to the genus Fusarium have been found to be the most common cause. Pythiwm debaryanum Hesse and species of Rhizoctonia have also been found to be important damping-off pathogenes in certain cases. In Europe, 4 MANUAL OF TREE DISEASES Phytophthora omnivora de Bary is the most common on both coniferous and deciduous tree seedlings. This latter fungus is widely distributed in this country and may be found to be of importance with further investigations on deciduous seedlings. It is to be assumed that many other species of fungi may also at times produce damping-off in tree seedlings, since Thielavia basicola (B. and Br.) Zopf and species of Botrytis, Colle- totrichum, Volutella and other fungi have been discovered producing this disease in seedlings of other crops. Numerous inoculation experiments by various workers have established the power of the above mentioned pathogenes to cause this type of disease. The causal fungi represent many widely different types of life history. The parasitism of these fungi is of a very primi- tive sort. This is evidenced by their usual saprophytic char- acter, extreme destructiveness to the host-plant, wide host- range and the fact that they are limited in their activities to very young seedlings, which have not developed the more com- plex physical and chemical nature of older plants. These fungi exist ordinarily as common saprophytes on decaying vegetable matter in the soil and thus their mycelium is the main infective material. Various types of spores are formed by the different species of fungi concerned in damping-off, but they are rarely instrumental in the inoculation of healthy plants. These spores, however, are mainly useful in carrying the fungus over winter and through other conditions detrimental to vegetative growth. The entire life history of these fungi then, so far as explaining the appearance and development of damping-off in seedling-beds, is confined largely to the growth of the mycelium through or on the surface of the soil, from one plant to another. This manner of spreading is often well il- lustrated when all the plants in a single row are destroyed and only occasional plants in the adjacent rows are affected. Al- though some one or several of the damping-off fungi are generally SEEDLING DISEASES AND INJURIES 5 present in all soils, their presence may not become evident if conditions are adverse to their development. All damping-off pathogenes are markedly influenced by temperature, soil moisture and the humidity of the atmosphere. A relatively high temperature, moist and compact soil and a humid at- mosphere furnish ideal conditions for these fungi, while lower temperatures and drier conditions of soil and atmosphere may check successfully a destructive development of these organisms after some damage has already been accomplished. Control. Since damping-off may be caused by any one of numerous species of fungi and may occur under such variable conditions, no general rules for treatment can be prescribed which will apply in all cases. The control of damping-off may be effected by one of two general methods: (1) protection of the seedlings by maintaining conditions of temperature and moisture which interfere with the destructive development of the pathogenes ; (2) eradication of the pathogenes from the soil of the seed-bed by means of disinfectants. (1) Protection. Every investigator agrees that much can be accomplished in the control of damping-off by giving careful attention to the manipulation of soil moisture, temperature and atmospheric humidity. At the same time, it is realized that one may find it difficult, in regulating the amount of moisture and other factors, to preserve the equilibrium necessary to grow seedlings, and at the same time to prevent the growth of the fungi. The following method of procedure is advised : Each seed-bed should be provided with upright frame, with wire-mesh sides and removable top, which can be made into half-shade or full-shade by laying on laths. The seed should be sown on the surface of the prepared soil and covered to the desired depth with clean dry sand 6 MANUAL OF TREE DISEASES obtained by digging three or four feet below the surface. This furnishes a surfacing for the bed which is sterile and easy to keep relatively dry. The beds should be covered and kept moist enough to pro- mote germination. After the seeds have germinated, partial shade should be furnished on bright days but should be removed in cloudy weather, in order to allow as much evaporation as possible from the surface of the soil. These precautions are especially important if it is warm and rainy. If the surface of the soil does not dry sufficiently, more clean coarse sand may be scattered over it. (2) Eradication. Two general eradication methods are recommended for the control of damping-off: (1) disinfection of the soil before planting, usually with formaldehyde; and, (2) for coniferous seedlings only, disinfection at the time of planting with sulfuric acid. If damping-off has previously occurred in a bed, the best practice is to remove the top-soil and substitute new soil. This is desirable since a large accumulation of the resting spores of the causal pathogene is to be expected after a severe outbreak. The following steps are essential for thorough disinfection : A solution of formalin should be made by adding one gallon of formalin (which should contain forty per cent formaldehyde by volume) to fifty gallons of water. The soil should be prepared by forking or raking. The formalin solution may then be applied to the bed with a sprin- kling-can, using about two quarts for every square foot of soil to be treated. If the nature of the soil is such that this amount cannot be put on in one application, as much as possible should be applied without making the soil muddy and the remainder added a few hours later. The bed should be covered as securely as possible with heavy paper or other impervious material for forty-eight hours. SEEDLING DISEASES AND INJURIES 7 The active substance in the formalin solution is liberated as a gas (formaldehyde). The cover is necessary in order to retain this gas in the soil for a period sufficient to kill the pathogenes. Three or four days after the cover is removed, the soil should be thoroughly forked and allowed to stand in a loosened con- dition for another day or two, after which the bed may be prepared for sowing the seed. It is important to time the application of the formalin so that the seed may be sown as soon as the operations above described are completed, since the soil may become contaminated again from surrounding soil. Experience shows that beds contaminated after dis- infection may exhibit greater loss than those not disinfected. The increased virulence of damping-off fungi in disinfected beds is thought to be due to the lack of competition with other soil organisms which have been killed by the disin- fectant. With ordinary care, however, under most condi- tions a clean crop of seedlings is assured if the disinfection is thorough. Even after carefully disinfecting the soil, all the measures advised above under Protection should be ob- served (see page 5). The application of sulfuric acid to the soil at the time of seeding has given good results in controlling damping-off in coniferous seed-beds. Sulfuric acid should never be used on deciduous seedlings. The amount of acid used with safety will necessarily vary with the natural acidity or alkalinity of the soil. A too heavy application of sulfuric acid will cause injury to the seedlings. This method is more difficult to handle than the formalin treatment because in loose sandy soils the capillary movement of the water will bring the acid to the surface and produce there a concentrated solution, which must be counteracted by daily watering. With heavier soils, no wa- tering seems necessary from the experiments so far reported. With the two uncertain factors in mind, the natural acidity or alkalinity and the physical nature of the soil to be treated, 8 MANUAL OF TREE DISEASES the grower must experiment under his own conditions before applying this method generally, else the chemical injury by the acid to the seedlings may be greater than the losses due to damping-off if no treatment were used. If this method can be handled without damaging the seedlings, two special ad- vantages are gained over the other two methods given above. In the first place, dicotyledonous weeds rarely grow in the acid soil and the saving of the expense of weeding will often pay for the treatment. Secondly, the disinfectant is present in the soil throughout the critical damping-off period. This assures complete control since contamination of the beds from neigh- boring soil is not possible and, moreover, conditions of tempera- ture and moisture favorable to seedling growth can be provided without danger. The average amount of sulfuric acid is three-sixteenths of a fluid ounce of clear commercial sulfuric acid to each square foot of soil to be treated. A solution is made by adding three- sixteenths of an ounce of the sulfuric acid to each quart of water (this is at the rate of one part of acid to 170 parts of water). This solution should then be applied when the seed is sown at the rate of one quart to each square foot of soil. If the soil is light and sandy and conditions are favorable for excessive evaporation, light watering once or twice a day may be neces- sary to prevent acid-injury. In heavier soils no watering may be necessary. The strength recommended above is suffi- cient to disinfect a soil which is not strongly alkaline. If the soil is naturally acid, the three-sixteenths of an ounce to each square foot may be too much. It would, therefore, be advisable to divide a given bed into three parts, applying sulfuric acid to each part respectively in the following quantities, one-eighth, one-fourth and three-sixteenths of an ounce in a quart of water to each square foot. From this experiment it may be deter- mined which strength can be safely employed under the exist- ing soil conditions. SEEDLING DISEASES AND INJURIES 9 REFERENCES ON Dampinc-OFFr Hartley, Carl, and Pierce, R. G. The control of damping-off of conif- erous seedlings. U.S. Dept. Agr. Bul. 453: 1-32, pls. 1-2, fig. 1 1917. Johnson, James. The control of damping-off disease in plant beds. Wisconsin Agr. Exp. Sta. Research Bul. 31: 29-61, figs. 1-12. 1914. Gifford, C. M. The damping off of coniferous seedlings. Vermont Agr. Exp. Sta. Bul. 157: 1438-171, pls. 1-4, figs. 1-10. 1911. Jones, L. R. The damping off of coniferous seedlings. Vermont Agr. Exp. Sta. Ann. Rept. 20: 342-347. 1908. Hartley, Carl. Injury by disinfectants to seeds and roots in sandy soils. U.S. Dept. Agr. Bul. 169: 1-35, pl. 1, figs. 1-2. 1915. Spaulding, Perley. The damping-off of coniferous ewes Phyto- pathology 4: 73-88, pl. 6, figs. 1-2. 1914. Hartley, Carl, and Merrill, F. C. Preliminary tests of disinfectants in controlling damping-off in various nursery soils. Phyto- pathology 4: 89-92. 1914. Pettis, C. R. Problems in nursery practice. Proc. Soe. Amer. Fores- ters 4: 43-44. 1909. Seott, Chas. A. 4 6 oxidation products which stain the mycelium and cell-walls of the wood. The mycelium of wood- rotting fungi uses the dissolved wood-tissue as food material. After a considerable amount. of this food is obtained and stored, the production of the fruiting-bodies be- gins. For this purpose a tissue-like development of closely tangled my- celium, in the shape of ms a knob, usually forms at ae the original point of in- Fra. 5.— Under surface of a polypore, show- fection. The food ma- ae Sper Gade of Beer eG ate tubes. En- terials from all directions arged (several times). are transported to this point and the fruiting-body develops an upper sterile surface and a fertile suspended layer of spore-bearing tissue on the under surface. In the case of the toadstools the spores are borne on the sides of pendent plates or gills (Fig. 8, page 81), and in the bracket-fungi or polypores, they are borne on the inner sur- face of perpendicular tubes which are open at the lower end and are visible to the naked eye as small holes in the lower surface of the fruiting-body (Fig. 5). Besides the character- istic action of the mycelium of the different species of fungi t BODY AND BRANCH DISEASES AND INJURIES 69 causing the wood-rots, the characters of the fruiting-bodies serve to identify the causal fungus, if they are definitely as- sociated with the rot. The correct determination of the dif- ferent species of bracket-fungi is, however, not easy in some cases. The number of species of annual forms represented in the United States is greater than that of the perennial forms. A generic distinction between the annual and perennial forms is recognized and they have been named respectively Po- lyporus (po-lip’-pore-us) and Fomes (fo-meez). Other genera have been split off from these two, which probably represent a more natural classification. Since, however, the simpler and more artificial classification is still used by laymen and most scientists, the genera Polyporus and Fomes are used in the discussion of the wood-rot fungi in this book. For a synonymy of polypore names, see the appendix, page 364. The species of Polyporus usually produce a more or less fleshy or corky fruiting-body which is soon destroyed by insects or decay and rarely functions in producing spores for more than the single season. The species of Fomes, on the other hand, form hard, woody structures which develop a new layer of tubes on the under surface each year as long as food material is being obtained by the mycelium, in its advance into normal wood. In this manner the size of the fruiting-body increases yearly and its age may be determined by counting the layers of tubes when the fruiting-body is split perpendicularly. Dissemination of the spores. The spores of the bracket-fungi are borne in groups of four, each on a tiny spine, at the ends of branches of the mycelium which project from the inner sides of the tubes. * When mature, these spores are shot from their attachment with just enough force to bring them to the center of the tube, and then they drop_out of the open end at the bottom. The wind, or even the slightest breeze, serves to carry the spores for long distances, 70 MANUAL OF TREE DISEASES since they are very light and buoyant. Millions of spores are disseminated from a single fruiting-body during a few days after they become mature. They are somewhat sticky and adhere to any object with which they come in contact. The larger part of them never reach suitable places where infection may be accomplished. However, a sufficiently large number is produced that a few usually find lodgment where infection is possible. Wounds such as the splintered ends of the branch- stubs which hold moisture readily are most likely to become infected. The spores are very short-lived and suitable con- ditions of moisture must be encountered in order to have ger- mination take place. The germ-tube of the spore produces short branches of mycelium which immediately begin the decay of the wood at the point of infection, and as soon as a firm foot- hold is gained, a copious growth of the mycelium occurs, which spreads rapidly. Control of wood-rots. Wood-rot diseases are more abundant and destructive in the forest than in individual trees grown for shade or ornament. Conditions in the forest are ideal for the development of these fungi. All sorts of wounds are available for infection and thus dissemination and germination of the spores is more efficient in causing a higher percentage of infection. Another factor which makes wood-rots more serious in the forest is that great quantities of fallen trunks and branches are present on which fruiting-bodies of most of the wood-rot fungi continue to be produced in great abundance. Outside the forest, the absence of these conditions makes infection less common. A few of the wood-rots, however, are important diseases of shade-trees. In controlling these rots, tree surgery methods are effective if the wood-rot is not too far advanced and if the expense is considered justified by the value of the tree. The methods for eliminating heartwood- and sapwood-rots are discussed under BODY AND BRANCH DISEASES AND INJURIES ‘771 tree surgery, page 345. The necessary care in pruning to leave a wound which will heal most rapidly and protecting the wound in the meantime by the use of wound-dressings are important measures for reducing wood-rots to a minimum. These opera- tions aré also more fully discussed under tree surgery methods. The immediate destruction of newly developing fruiting-bodies of all kinds in the vicinity of trees to be protected will reduce greatly the amount of infection. In the forest, the factors concerned in the complex of soil, atmospheric and biologic relations, influence greatly the yield and quality of timber that is realized. Methods of forest management in this country have seldom taken into consid- eration many of these vital factors, one of the most important of which is the control of the wood-rotting fungi of living trees. The subject of forest pathology is too complex to be adequately dealt with in a small space and is outside the field of this book. A simple method of disease control in the forest is the elimina- tion of all diseased trees at the time cutting operations are in progress. For some types of forests and systems of selec- tion for cutting, this procedure is not economically possible. Thus it will be possible to control the loss factor due to decay only when all the complex relations existing. in the forest have been studied for different types and localities. Before control measures can be incorporated into scientific forest regulation, such points as the following must be determined: the relations which determine the rate of growth and general health of the trees, the extent, nature and cause of wounds, the life history of the wood-rotting fungi, the relative susceptibility of different species and different age classes, and many other relative factors. REFERENCES Schrenk, Hermannvon. Fungous diseases of forest trees. U.S. Dept. Agr. Yearbook 1900: 199-210, pls. 21-25. 1901. Meinecke, E. P. Forest pathology in forest regulation. U.S. Dept. Agr. Bul. 275: 1-62. 1916. CHAPTER IV ROOT DISEASES AND INJURIES Tue roots serve both for anchorage and for gathering from the soil the water and dissolved raw materials needed by the tree in its growth. The structure of certain types of soil, and the food materials contained, often determine the kinds of trees which will grow best in it. However, it is not the intention to discuss here the adaptability of different species to soil-types or of the poor growth or injuries resulting from a lack of such adaptability. Although a tree may be growing in suitable soil and obtaining from it the proper materials for normal growth, there are other factors which often inter- vene to cause injuries to the root system. Any such injuries to the roots of the tree may impair certain functions or destroy living tissues and cause various symptoms of disease to appear in the aérial portions of the tree. In diagnosing tree troubles, the possibility of root diseases should be considered and care should be taken to ascertain whether or not the condition of the roots may be the primary cause of the difficulty. Impairment of the root functions may be due to such conditions as : too much water in the soil, causing drowning; too little water because of sod, pavements, or packed soil above the roots; poisonous gases or over-abundance of certain food materials applied to the roots with fertilizers; and the attacks of certain parasitic fungi and bacteria which invade and kill living tissue. These various injurious factors work more or less slowly, and the usual symptoms noticed in the parts above ground are: slow growth, thin foliage, sun-scorch of the 72 ROOT DISEASES AND INJURIES is leaves, early fall of leaves in autumn, death of certain entire branches, stag-head, and lichens on the bark. When such general symptoms of decline occur without apparent associa- tion with a cause in the branches, leaves or atmospheric con- ditions, the presence of a root trouble may be suspected. DRYING AND DROWNING Caused by too little and too much water in the soil Trees must obtain at all times enormous quantities of water from the soil, during the period when the leaves are expanded. With a normal water supply and a healthy root system, a tree is naturally so balanced in its development of roots and leaf- surface, that it is able to supply the water lost in transpiration from the leaves, except under the most abnormal atmospheric conditions. But if the supply of water is limited because the natural rainfall does not soak into the soil, the leaves may tran- spire more water than the roots can take up ina given length of time. This condition will cause sun-scorch of the leaves and if repeated year after year may cause the death of the tree (see page 22). The other extreme of too much water in the soil may result in more speedy death of the tree. The tips of the roots, which are in contact with the soil-particles and absorb water and food materials, must at the same time obtain a ready supply of air to make healthy growth and perform their function of absorp- tion. The older parts of the roots must also have access to a supply of air in order that the living tissues they contain may function in growth and transporting food materials and water to the parts above ground. If the amount of water in the soil is excessive, it drives out the air, thus disturbing the balance of air and water necessary to plant growth. This results in slow or rapid death of the roots by drowning. The leaves may show sun-scorch injury the same as when too little water is present. 74 MANUAL OF TREE DISEASES This may seem peculiar, since there is an over-abundance of water in the soil, but it is explained by the fact that the trans- porting of the water to the trunk is dependent on the healthy condition of the roots and when these are injured, the power to absorb water is diminished accordingly. Therefore, al- though there is plenty of water in the soil, it cannot be supplied to the leaves. The remedy for such conditions of abnormal water supply may be undertaken after the symptoms are noted, if the re- covery of the tree seems possible. When heavy sod, tight paving or compact soil is the cause of too little of the normal rainfall reaching the roots, artificial means must be used for watering. The best method is to keep the sod broken up, but when this is not desirable, upright sections of tile may be placed at intervals flush with the sod and the necessary water furnished by running water into these from a hose. It should be remembered that the feeding rootlets are under the edges of the branches and not up close to the trunk of the tree. The tile should, therefore, be placed at intervals in a circle under the tips of the branches. A certain amount of artificial fertilizing may also be accomplished through the tiles. When the soil contains too much water, the ordinary methods of drainage should be employed. REFERENCE Graves, A. H. Root rot of coniferous seedlings. Phytopathology 5: 213-217, figs. 1-2. 1915. FREEZING-TO-DEATH Caused by low temperatures Many kinds of trees are more or less injured by the freezing of the roots. White pine, maple, elm and ash are particularly susceptible. ROOT DISEASES AND INJURIES 19 Symptoms. The symptoms of freezing-to-death in the roots, as noticed in the aérial parts, are general, although somewhat distinctive and diagnostic. The primary symptoms can easily be deter- mined by examining the roots themselves. Tissue which has suffered from freezing-to-death gives no external evidence of its condition until some time after it has thawed. Then it ap- pears, at first, water-soaked and later, after some disintegration processes have set in, it becomes brown. Tissue thus killed is soon invaded by the numerous saprophytic organisms in the soil and is further disintegrated. Severe injury to the entire root system results in the death of the tree before summer. The leaves may come out, but re- main small and misshapen. Less severe and re-occurring in- jury to the roots may result in a varying succession of symptoms. One of the most common effects is that of sun-scorch of the leaves, and is most common in the pine and maple (see page 22). The inability of the remaining healthy roots to provide enough water for the leaves to equal the amount transpired on hot days results in the wilting and death of the leaves. The entire tree suffers then, since the diminution of the leaf-surface makes im- possible the manufacture of enough food materials for normal growth. Another symptom of root-injury is the production of thin foliage at the top, in excurrent trees, and stag-head may be the cumulative effect of this condition. Cause of freezing-to-death. In the process of maturing the new tissue formed during the summer, the roots are the last part of the tree to attain the con- dition necessary to withstand low temperatures without injury. A combination of-a late warm autumn followed by deep freez- ing of the ground may lead to serious root damage. Thus, it happens that winter-injury to the roots 1s exceptionally common some winters and rare in others when the temperature falls to 76 MANUAL OF TREE DISEASES even a lower point. The injury caused to the roots is the type known as freezing-to-death (see page 12). The water in the cells is withdrawn during the formation of ice crystals between the cells. As the temperature becomes lower, the physical pull incident to ice formation causes a larger amount of water to be withdrawn from the living cells than they can endure without being killed. Since the root system of most kinds of trees may extend from a few inches to several feet below the surface, it is natural that shallow-rooted trees will show the first and most serious injury provided the minimum temperature for the roots of that species is reached. Also, the amount of damage to the root system of a given tree depends on whether its roots are largely superficial or are found at varying depths. Control. Winter-injured roots should be uncovered and the dead parts pruned off. The wounds should be treated with a wound- dressing, and the soil conditions around the tree made con- ducive to the rapid regeneration of new roots by fertilizing. Mulching may be practiced to protect the soil around sus- ceptible trees from freezing deeply. REFERENCE Stone, G. E. Winter injuries of roots. Jn Shade trees, character- istics, adaptation, diseases and care. Massachusetts Agr. Exp. Sta. Bul. 170: 200-204. 1916. Gas-INJURY Caused by illuminating gas Trees are commonly injured by the poisonous effect of illumi- nating gas on the roots, when leaks in gas-pipes are not promptly repaired. The effect is usually cumulative and the tree may show no sign of the injury until some time has elapsed. ROOT DISEASES AND INJURIES C0 Symptoms. The symptoms are general in nature, being about the same as those produced when any agency causes a gradual death of the root system. Partial freezing-to-death of the roots and cumulative gas-injury cause similar symptoms. The turning yellow or brown of the foliage is a common symptom, probably due entirely to the interference with the conduction of the necessary supply of water. Later, the living tissues m the root and trunk will be found dry and turning brown, showing that the lack of water and the poisonous properties of the gas com- bined have killed the tissues. At this stage various branches die and saprophytic fungi attack the dead bark. The length of time which it takes for a tree to die from gas-poisoning de- pends entirely on the amount of gas in the soil. Even a small quantity of gas present continuously will produce serious injury within two or three years. Conifers are much more resistant to gas than deciduous trees. At times, the former recover after the injury becomes apparent, while deciduous trees which begin to develop the symptoms of poisoning rarely recover, even if the leak is repaired. Cause. The injury to the roots caused by illuminating gas is probably of two kinds: first, true asphyxiation, since the air necessary to the roots is replaced by the gas; and second, the living tissues are poisoned. Many toxic substances are contained in the dif- ferent kinds of illuminating gases. These substances when dissolved in the soil-water are absorbed into the root and the cumulative effect is shown in the death of the cells. Control. The remedy for gas-injury is to stop the leakage and stir the soil until all the gas has escaped. If only a portion of the root system and trunk is killed, the tree may be saved by the use of - surgical methods to remove the dead tissue (see page 345). 78 MANUAL OF TREE DISEASES REFERENCES ON Gas-INJURY Stone, G. E. Effects of illuminating gas on trees. Jn Shade trees, characteristics, adaptation, diseases and care. Massachusetts Agr. Exp. Sta. Bul. 170: 220-228, figs. 938-97. 1916. Stone, G. E. Effects of illuminating gas on vegetation. Massa- chusetts Agr. Exp. Sta. Ann. Rept. 25:1: 45-60, figs. 1-8. 1913. SHOE-StRING Root-Rot Caused by Armillaria mellea (Fries) Quelet The shoe-string or honey-mushroom root-rot is common throughout the United States on many kinds of coniferous and deciduous trees. It has been noted especially on oak, pine, chestnut, larch, sycamore, poplar, locust, hemlock, birch, alder, maple and many kinds of fruit-trees and shrubs. In some sections of the country, especially in south central United States and on the Pacific Coast, orchard-trees are commonly affected and killed. The disease is most destructive in orchards on land recently cleared of oak. In Europe this disease is also common on cedar, pine, fir, peach, cherry, olive, grape and many other kinds of woody plants. There seem to be no. definite host relations for the activities of the fungus causing this root-rot. It is known to attack the potato. No very accurate facts are available as to the parasitic po- tentialities of the honey-mushroom. It occurs everywhere .on stumps and dead wood and is commonly found on trees in poor health or badly wounded. The relation between the decline of the tree and the attack of this fungus is hard to determine. However, abundant evidence is at hand that young thrifty trees in the forest and orchard are often killed, when there is no doubt that the honey-mushroom was directly and primarily the cause of the decay of the roots. It is, therefore, reasonable to expect that on further investigation this root-rot will be fully shown to be a primary cause of the decline and death of the trees. In many cases, however, it may play only a sec- » signs of decline to final death mycelium of the causal fungus ROOT DISEASES AND INJURIES 79 ondary part. The fungus is so prevalent as a saprophyte that its occurrence as a wound parasite and root-rotting fungus on trees 1s not surprising. Symptoms. The bark and wood of the roots are affected and the living tissues destroyed. The decay may also extend up into the bark and sapwood of the lower part cf the trunk (Fig. 6). Trees with the root system partially destroyed display general symptoms of decline and poor health, such as dead limbs, scanty and light green foliage, and but little annual growth. In conifers a large amount of resin exudes from the base of the tree and ac- cumulates as a hard cake (Fig. 6). The time from the first may extend over a period of three or four or more years. There are many diagnostic symptoms by which this root- rot may be identified. The when growing in the soil out- side the roots is bound to- gether in long round, blaek Fie. 6.— White pine killed by shoe- = string root-rot. strands somewhat resembling shoe-strings. These black strands may be found growing attached to the bark of the roots and trunk or running through the soil for long distances away from the affected 80 MANUAL OF TREE DISEASES roots (Fig. 6). The strands may be traced to points at which they enter the roots. At these points the white mycelium in- side the black strands spreads out and runs in all directions in the bark and sapwood. Thin white sheets of mycelium are found in the cambium region (Fig. 6). The tissues of the cambium and bark are destroyed and replaced by the white sheets. The mycelium also penetrates the medullary-rays and sapwood and causes a wet white rot. After the bark is killed, the black shoe-strings are formed abundantly between the bark and wood. ‘They anastomose in all directions and form a network. The decayed area of sapwood and bark is bordered by a_ brown zone. The fruiting-bodies of the fungus are honey-colored toadstools or mushrooms. They appear on the sides of the trunk, exposed roots or directly from the ground. _ Close examination will show their attachment to the Fic. 7.— Young toadstools of Armillaria 2 5 mellea attached to shoe-strings. black shoe-strings (Fig. a: The toadstools occur in ~ clusters, attached to one another at the base of the stalks. - The stalks are somewhat swollen at the base and have a fragile collar just beneath the cap. The upper surface of the cap is smooth and yellowish or brownish. The under surface is composed of radiating pendent plates or gills of the same color (Fig. 8). Cause. The shoe-string root-rot of trees is caused by the mushroom, Armillaria mellea. The spores are borne on the sides of the ROOT DISEASES AND INJURIES 81 gills or plates on the under surface of the fruiting-body (Fig. 8). The tree-roots are infected in several ways. The spores may cause infection through wounds at the base of the tree or in ex- posed roots. The black strands running through the soil may also penetrate the bark of the roots. In this manner the fungus spreads through the — soil from the roots of one tree to another. This mode of infec- tion accounts for the occurrence of circular areas of dis- eased trees. Since the fungus also com- monly occurs as a saprophyte on dead wood, the fruiting- bodies are produced in great abundance on prostrate trunks and on old stumps for ‘several years after the affected Fic. 8.— Mature fruiting-body of Armillaria mellea, tree is dead. showing gills on under surface. Control. Root diseases are difficult to control since the condition of the roots cannot be readily ascertained. By destroying the toad- stools and removing the diseased roots or parts of roots, the individual tree may be saved. In the orchard or forest, dis- ~ eased trees or groups of trees may be surrounded by isolation G 82 MANUAL OF TREE DISEASES trenches, a foot or two deep. All roots bridging the trench must be removed and the trench kept free of débris and fruit- ing-bodies. The trench must be dug far enough away from the affected trees to insure the absence of diseased roots out- side of the area to be isolated. — + REFERENCES Long, W. H. The death of chestnuts and oaks due to Armillaria mellea. U.S. Dept. Agr. Bul. 89: 1-9, pls. 1-2. 1914. Schrenk, Hermann von, and Spaulding, P. . Root-rots. Jn Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 22-24, 1909. Hesler, L. R., and Whetzel, H. H. Armillaria root-rot. Jn Manual of fruit diseases, pp. 96-102, figs. 26-27. 1917. Hartig, R. Agaricus melleus L. Jn Die Zersetzungserscheinungen des Holzes ete., pp. 59-62, pl. 11. 1878. Hartig, R. Agaricus (Armillaria) melleus Le In Wiechtige Krank- heiten der Waldbaume, pp. 12-42, pls. 1-2. 1874. Lawrence, W. H. Root diseases caused by eats mellea in rie Puget Sound country. Washington Agr. Exp. Sta. Bul. (special series) 3: 1-16, figs. 1-5. 1910. Piper, C. V., and Fletcher, S. W. Root diseases of fruit and other trees caused by toadstools. Washington Agr. Exp. Sta. Bul. 59: 1-14, figs. 1-5. 1903. Horne, W. T. The oak fungus disease of fruit trees. California State Com. Hort. Monthly Bul. 3: 275-282, figs. 79-81. 1914. Horne, W. T. Fungous root rot. California State Com. Hort. Monthly Bul. 1: 216-225, figs. 85-91. 1912. Horne, W. T. Oak fungus or Armillaria mellea in connection with nursery stock. California State Com. Hort. Monthly Bul. 4: 179-184, figs. 31-33. 1915. Barss, H. P. Mushroom root rot of trees and small fruits. First Biennial Crop Pest and Horticultural Report (Oregon Agr. Exp. Sta.) 1911-1912 : 226-233, figs. 23-38. 1913. Mycoruizas Caused by various species of fungi An interesting type of parasitic relation between certain species of fungi and the living roots of many kinds of trees con- ROOT DISEASES AND INJURIES 83 sists in the development of mycorhizas. These structures probably in no manner interfere sufficiently with the growth of the roots to cause any damage. ‘Trees with mycorhizas on the roots cannot be distinguished from those without by any above- ground symptoms. A short account of them is, however, of interest since the structures are now generally considered to represent a diseased condition of the roots and not a true type of symbiosis or mutual-advantage relation, as was previously believed by many. The term mycorhiza is used to signify the infected root and the mycelium of the fungus, as an association of two distinct but physiologically interdependent tissues. This usage is thus similar to the use of the term lichen, the formation of which requires the association of certain algze and fungi to form the characteristic structures known as lichens. Mycorhizas are of two types: ectotrophic, when the mycelium forms a mantle or sheath around the root-tip and penetrates the tissues by inter- cellular (existing between the cells) threads of the mycelium ; and endotrophic, when the mycelium is within the tissue and is largely intracellular (within the cells). Recent investigations have shown that hickory, oak, basswood, birch, larch, poplar and beech commonly show ectotrophic mycorhizas, and species of maple, butternut and horse-chestnut have endotrophic forms. Elm and species of willows were found not to have mycorhizas. This list is by no means complete, but represents the species reported in the reference given below. With the exception of this work, little is reported in American literature on mycorhi- zas. European literature on the subject, however, is abundant. Both types of mycorhizas are annual. The mycelium of the species of fungi capable of forming mycorhizas penetrates the young root-tips in the summer. The association with the root- tissues is rapidly formed and food materials are obtained by the fungus. Later, the fungus may produce a growth of mycelium in the soil in the autumn, in which case fruiting-bodies are 84 MANUAL OF TREE DISEASES formed on the surface of the ground. Several kinds of toad- stools and puff-ball fungi have been proved to be mycorhizal fungi. Ectotrophic mycorhizas are recognized by the short, stubby, lateral rootlets, which are covered with the fungus mantle and may be white, brown, yellow or red. The same tree may show several different kinds of mycorhizas, each caused - by a different species of fungus. When the mycorhizal pro- duction is profuse, whole clusters of the stubby roots may form a coral-like structure. The endotrophic mycorhizas on maple roots form bead-like swellings, often in chains. The mycelia of some endotrophic mycorhizas have been found to produce fruiting-bodies, which place them in the genus Phoma. REFERENCE McDougall, W. B. On the mycorhizas of forest trees.. Amer. Jour. Bot. 1: 51-74, pls. 4-7, fig. 1. 1914. (Bibliography given.) Roots PARASITIZED BY FLOWERING PLANTS Several species of flowering plants attach their root-like organs to the roots of other plants and trees, and draw a certain amount of food materials from them. All degrees of para- sitism are found, from the species of the broom-rape family (Orobanchaceee) which develop no leaves or chlorophyl and are entirely dependent on other plants for food, to those types which develop normal green foliage above ground, and some- times grow without forming any attachments to the roots of other plants. Certain species of Comandra have been found to be of the latter type. Their roots normally develop disc- like attachments, which connect the tissues of the Comandra roots with the roots of various other plants. They have been found attached to the roots of the following trees: maple, birch, chestnut, poplar, oak and sumac. Very little damage is done to the tree. Examples of the former type, mentioned ROOT DISEASES AND INJURIES 85 above, where all the food materials required by the plant are obtained through the connected roots, include the common beech-drop (see page 108), indian-pipe and many other plants belonging to various families of the flowering plants. REFERENCES Hedgecock, G. G. Parasitism of Comandra umbellata. Jour. Agr. Res. 5: 133-135. 1915. Harshberger, J. W. Vegetal agents of disease. Jn A text-book of mycology and plant pathology, pp. 298-306, figs. 117-123. 1917. CHAPTER V ALDER DISEASES SEVERAL native species of alder (Alnus) are common forest- trees in the Northwest and Rocky Mountain region. They grow in river-bottom lands and on mountain sides. In eastern United States, the European alder is used as an ornamental and in some localities has become naturalized. The alder is particularly subject to wood-rot diseases. The common white and the brown checked wood-rots often cause death by destroying the sapwood. The leaf-blisters, deforma- tion of the catkins and catkin powdery mildew attract attention when they occur, but they do only slight damage to the tree. The alder also is one of the non-leguminous plants on which the nitrogen-fixing bacteria form root-tubercles. The several shrubby species of alder are subject to the same diseases as the larger trees. PowpERY MILDEW oF CATKINS Caused by Erysiphe aggregata (Peck) Farlow In northeastern United States, the female catkins of alder are often covered with a powdery mildew. A similar, if not identi- cal, fungus attacks the twigs of alder in Europe. The catkins are covered with a white or yellowish coating of mycelium which later may be dotted with clusters of small black fruiting-bodies. The life history and methods of control of the powdery mildew fungi are discussed on page 37. Two other species of the pow- dery mildews occur on alder leaves. 86 ALDER DISEASES 87 CaTKIN-DEFORMATION Caused, by Hxoascus amentorum Sadebeck The catkins of several species of alder are affected by this disease. ‘The same disease is common in Europe. The scales of the fertile catkins become much enlarged and project as curled, reddish tongues. Later they are covered by a white glistening coat of the fruiting structures of the parasite. The mycelium is perennial in the twigs. Practically no damage is done to the tree. If preventive measures are desired, the prun- ing of the diseased parts should eventually eliminate the difficulty. Brown CHECKED Woop-Rot Caused by Polyporus sulphureus Fries The alder is one of the many deciduous trees commonly af- fected by the brown checked wood-rot. Chief among the other kinds affected are oak, chestnut, walnut, butternut, maple and locust. The causal fungus enters through some wound where the heartwood is exposed. The heartwood and sapwood are both decayed and become like red-brown charcoal. Thin yellowish sheets of mycelium, within concentric and radial checks, divide the decayed wood into small punky cubes. The fruiting-bodies emerge, usually, from old branch wounds and consist of many overlapping shelves forming a large, more or less globose mass. The upper surfaces of the shelves are orange- red, while the under surfaces are sulfur-yellow. For further de- tails concerning this wood-rot see under oak diseases, page 247. Common Wurte Woop-Rot Caused by Fomes igniarius Fries Alders are destructively affected in Europe by the common . white wood-rot. In the United States such trees as beech, 88 MANUAL OF TREE DISEASES poplar, willow, maple, butternut, walnut, oak and hickory are the most commonly affected by this wood-rot. Specific men- tion of this disease in alder is less frequent in this country be- cause of the slight economic importance of the species of alder. For a description of the symptoms of the common white wood- rot, see under poplar diseases, page 305. Root-TUBERCLES Caused by Bacillus radicicola Beijerineck The roots of alder commonly show large clusters of short stubby roots. These abnormal roots represent a diseased con- dition by which the alder benefits. The dwarfed roots are in- habited by the same bacterium which causes the root-tubercles of clover, bean, cowpea, locust and other leguminous plants. The bacteria gain entrance to the young lateral rootlets by way of the root-hairs. They multiply within the cells of the cortex of the root and stimulate this tissue to over-growth. They live parasitically and obtain their food materials from the proto- plasm and cell sap of the alder roots, but they do not kil! the cells they inhabit. These bacteria take the free nitrogen gas from the air and combine it with other substances. After this is accomplished, the alder roots eventually receive this combined nitrogen and the tree uses it in its metabolic processes. In this way large quantities of nitrogen are obtained indirectly from the air by the alder. The higher plants cannot utilize nitrogen gas from the air and the plants which are parasitized by the nitrogen-fixing bacteria are thus greatly benefited. Such a mutual-benefit relation between the alder and the bacteria is known as symbiosis, although strictly speaking the bacteria are parasitic even though they do not cause the death of the root- tissues. REFERENCE Spratt, Ethel R. The morphology of the root tubercles of Alnus and Elwagnus, and the polymorphism of the organism causing their formation. Ann. Bot. 26: 119-128, pls. 138-14. 1912. CHAPTER Vi ARBOR-VITZ DISEASES Two species of arbor-vitee (Thuja) are common forest-trees in northeastern and northwestern United States. They occur in moist river-bottom lands and along mountain streams. The western arbor-vite grows to a much larger tree than the eastern species. Both species are extensively used as ornamentals. The eastern arbor-vite is especially free from diseases. The wood and roots of the living tree are seldom decayed and no leaf or twig-diseases of any importance are known. The western arbor-vite, on the other hand, is destructively attacked by a leaf-fungus. The younger trees may be killed outright. In the nursery, arbor-vite is subject to a common blight which also affects juniper. Ornamental arbor-vite seldom suffer from fungous diseases but frequently are injured by freezing-to-death, sun-scorch and other general troubles (see index). SEEDLING-BLIGHT Caused by Phoma sp. At least three species of Thuja, including the eastern and western arbor-vite, are affected by this seedling-blight. The same disease is common on juniper. Young arbor-vite trees up to four years old are affected in the same manner as juniper (see page 190). Cankers are formed which girdle the stem, causing the plants to die. The disease often becomes epiphy- totic and causes serious losses in nursery-beds. Control measures have not been determined. 89 90 MANUAL OF TREE DISEASES Lear-BiicHt Caused by Keithia thujina Durand The leaf-blight or black leaf-spot of western arbor-vite is common and destructive, especially to young trees, throughout its range in northwestern United States. In dense stands and in localities where humid conditions prevail, this disease causes the death of a large percentage of the seedlings less than four years old. In late summer the lower branches of older trees when affected by this blight appear as if scorched by fire. In some localities the foliage of the upper parts of the trees also may be affected. This is, however, essentially a disease of seedlings. The affected parts are those which are covered by snow until late in the season. Symptoms. In spring and summer the affected leaves show from one to three more or less circular brown cushions bursting through the epidermis. Later these bodies turn black. The affected leaves die and turn brown in late summer. The twigs bearing the brown leaves also fall, leaving the branches bare. In autumn the black bodies in the older leaves often fall out, leaving holes, and these leaves turn gray. Cause. The leaf-blight or black leaf-spot of the western arbor-vite is caused by the fungus Keithia thujina. This fungus is closely related to the tar leaf-spot fungi of maple and willow and the black-specked leaf-spot fungus of maple. The black fruiting bodies on the leaves crack open, irregularly, and expose the ascospore-bearing surface within. The ascospores are wind- blown and infection usually occurs in the autumn. Moist weather is necessary for the discharge of the spores. ARBOR-VITHA DISEASES 91 Control. Preliminary experiments seem to indicate that soap-bordeaux mixture applied to young trees, every ten days or oftener in the autumn, will greatly reduce the amount of infection. REFERENCES Weir, J. R. Keithia thujina, the cause of a serious leaf disease of the western red cedar. Phytopathology 6: 360-363, figs. 1-2. 1916. Durand, E. J. The genus Keithia. Mycologia 5:6-11, pl. 81. 1913. Brown Pocket HEARTWoop-RotT Caused by Fomes roseus Fries There are few statements in literature concerning the fungi which cause the decay of the wood and roots of arbor-vite. Mention is made of brown pockets of decay in wood of the trunk which are probably due to Fomes roseus. This fungus causes a heartwood-rot of fir, juniper, larch, spruce, pine, and hemlock. The fruiting-bodies have been found also on a few deciduous trees. The decay caused by this fungus is described under juniper diseases (page 204). The color of the decayed wood varies from dark to a lighter brown according to whether the normal wood is deeply colored or not. In some cases the similarity between the effects of Fomes roseus and Polyporus Schweinitzii may lead to confusion as to which is the true cause of the rot, unless the sporophores are found attached to the tree in question. Rep-Brown Root- ano Butrt-Ror Caused by Polyporus Schweinitzii Fries This is one of the few wood-rots of conifers which occurs in arbor-vite. Pine, fir, spruce, hemlock and larch are seri- 92 MANUAL OF TREE DISEASES ously damaged by this root disease throughout their range. The wood of the affected roots is at first yellowish and cheesy but later it becomes red-brown and brittle. The rot sometimes extends up into the trunk. A more complete description of this disease is given under pine diseases, on page 294. CHAPTER VII ASH DISEASES SEVERAL species of ash (Fraxinus) are common forest-trees in most parts of the United States. White, green and black ash are the important timber-trees. These are common throughout eastern and central United States. The same three species mentioned above are frequently used for shade and ornament. Ash is exceptionally free from destructive diseases. The rust of the leaves occurs sporadically and may assume an epiphytotic nature. Little damage is caused to the trees, however, unless defoliation occurs two or three years in suc- cession. Several parasitic fungi cause leaf-spots on ash (see page 29). Only one wood-rot is described as important in ash. This disease is rarely found in the East but is destructive on the western limits of the white ash. The slow growth which the ash makes in that region seems to predispose the trees to this disease. Where the trees grow more rapidly, they are seldom affected. The roots of ash frequently are killed by . low temperature (see page 74). LreaFr- AND Twic-Rust Caused by Puccinia fraxinata (Link) Arthur The leaf- and twig-rust of red, green and possibly other species of ash is striking because of its effect on the leaves and twigs and its epiphytotic nature. It is common, at least in eastern and central United States, but varies greatly in abun- 93 94 MANUAL OF TREE DISEASES dance from year to year. In central Iowa and eastern Nebraska, this disease was so abundant in 1885 that it was difficult to find leaves not affected. The next two summers scarcely any of the rust could be found. In 1888 it was again abundant in the same region. An epiphytotic of this disease was reported in 1887 around Washing- ton, D. C., with very little of the rust in that region the next year. No recent reports of such outbreaks have been published. Symptoms. This rust causes swellings which are irregu- lar or more or less globose. They appear on the petioles of the leaves and on the twigs ~ (Fig. 9). Swollen areas are also formed on the leaves which are much distorted. Soon after the swellings are formed they are covered by numerous blister-like protrusions, which break open, leaving cup-shaped areas filled fee Bee with yellowish powder (Fig. 9). This stage causal fungus on of the rust is called the cluster-cup stage. oS OREN The yellow powdery material is composed of the spores (eeciospores) of the fungus. The distortion of the petioles and leaves, covered with the yellow cluster-cups, make this disease conspicuous. Cause. Ash-rust is caused by Puccinia fraxinata. This fungus requires two kinds of host plants to complete its life history. The spores produced in the cluster-cups on the ash do not reinfect the ash, but must find lodgment on the marsh or cord-grasses (Spartina) in order to continue their develop- ment. On the grass plant, spores are produced which infect the ash the next spring. ASH DISEASES 95 Control. The disease will probably not be noticed until the cluster- cups have broken open and shed their spores. It would then be of no avail to destroy the diseased parts of the ash, since the spores have already been distributed. If practicable, ash trees should not be grown in the vicinity of marshy land where the Spartina grass-hosts grow. In the absence of the grass- host, so far as the life history of this rust is known, there is no chance of infection of the ash. Wuire Hrartwoop-Ror Caused by Fomes fraxinophilus Peck White ash is commonly affected by this heartwood-rot in parts of Iowa, Missouri, Kansas and Oklahoma, on the wes- tern limit of growth of this species. The disease is rarely found in eastern United States. West of the Mississippi River, where the white ash attains only three-fourths its normal size, ninety per cent of the trees are often found diseased; a fact which suggests some correlation between the condition of the trees in this region and their apparent greater susceptibility. The slow rate at which wounds heal, however, may be the predisposing factor which accounts for the greater abundance of the disease. Trees of all ages and especially those over seven inches in diameter are affected. Symptoms. The rotted area as seen in cross-section of the trunk is very irregular in outline and often is more extensive on one side of the tree. The normal wood of the white ash is light yellow. In the first stages of decay, the wood is stained brownish. Later the affected wood becomes whitish and is surrounded by a brown zone where the decay is extending into the normal wood. The spring-wood of each annual ring becomes 96 MANUAL OF TREE DISEASES white, while for a time the summer-wood remains brownish. Shortly, however, the summer-wood becomes whitish and in the final stages of the decay the wood is soft and crumbly. The perennial sporophores of the causal fungus are formed at old branch wounds. They are usually small bracket-shaped bodies. The upper surface is hard, dark brown or black and marked by concentric folds. The under surface is velvety, straw-colored and covered with large circular pores. The inner structure of the fruiting-body is white or light brown, according to its age. A new layer of tubes is added to the lower surface each year. Cause. The white heartwood-rot of white ash is caused by Fomes fraxinophilus. This fungus is rarely found on any other tree. Living green ash trees have been observed with the fruiting- bodies on them and it is possible that a rot of similar nature as that caused in white ash may be found in green and other ashes. The spores borne within the tubes on the under surface of the fruiting-body fall out of the pores and are blown about by the wind. When they find lodgment on exposed heartwood of the white ash, a new mycelium may be initiated. The initial stages in the decomposition of the fibers result in a brown liquid which stains the wood. Later this colored liquid disap- pears and the mycelium delignifies the cell-walls and dissolves most of the cellulose. The fungus is not known to occur as a saprophyte. For further details concerning the life history and control of the wood-rotting fungi of living trees, see page 64. REFERENCES Schrenk, Hermann von. A disease of the white ash caused by Poly- porus fraxinophilus. U. 8. Dept. Agr. Bur. Pl. Ind. Bul. 32: 1—20, pls. 1-5, fig. 1. 1903. Schrenk, Hermann von, and Spaulding, P. White heart-rot of ash caused by Fomes fraxinophilus. Jn Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 46-47. 1909. CHAPTER VIII BALD CYPRESS DISEASES Tue bald cypress or Taxodium is an important timber-tree in southern and southeastern United States. It is frequently used as anornamental. The pecky heartwood-rot is the only known disease of any importance which attacks this tree. Pecky Hrartwoop-Rot Caused by Fomes geotropus Cooke The pecky heartwood-rot of bald cypress is a common disease and is recognized by every one who handles cypress timber. The disease is also known by the names peggy-, botty- and bot- cypress and the peck or puck of cypress. Bald cypress trees throughout their range are more or less affected by this disease. It seems, however, to be more common and destructive in the extreme southern states. It has been estimated that one-third of the cypress timber available is damaged by this wood-rot. Older trees are most often affected and, in many cases, the tops of the trees are decayed without damage to the principal timber portion. The number of trees showing more or less peckiness has been found to vary from practically 100 per cent of the stand in Florida and Louisiana to smaller percentages toward the northern limits of the range of cypress in North Carolina, In- diana and Missouri. Since the pecky wood has been found to be practically as durable as the normal unaffected wood, it is used for rough lumber and as ornamental finishing for rustic H 97 98 MANUAL OF TREE DISEASES effects. The general worm-eaten appearance of the pecky wood leads to the impression that the injury is due to wood- boring insects. Symptoms. The tops of trees one hundred and twenty-five years old or older are frequently affected. The rot is also found in the butts. Younger trees are rarely affected by this disease. The first indications of the rot are localized areas yellowish in color and about one-fourth inch wide and several inches long. The wood between the yellowish areas is unchanged. Decomposition of the wood elements in the yellow areas proceeds until definite cavities are formed. These cavities are partially filled with a yellow-brown powder and occasionally white mycelium and fibrous masses of partially decayed wood are found mixed with the brown powder. Sometimes the pockets are found entirely empty. The pockets extend lengthwise with the grain of the wood and are about one-fourth of an inch wide and four or five inches long. They are very smooth-walled and nearly cylindri- cal and blunt ended. Peckiness is usually confined to the upper ~ part of the trunk and older branches. In very old individuals, the wood at the base of the tree may be affected. The pockets are not always found at the center of the tree but may be located on one side or extend around the trunk leaving the center un- affected. The pockets may be several inches apart and scat- tered through the cross-section; or densely aggregated in the older wood or in certain annual rings. The badly affected trees are not appreciably weakened and are rarely blown over. ‘The wood between the pockets is slightly darker in color than the normal wood but it is unchanged structurally. Recently it has been learned that the hollows sometimes found in the butts or trunks of cypress seem to be due to the complete destruction of the wood between the pockets. The fruiting-bodies of the fungus causing the peckiness are \ BALD CYPRESS DISEASES 99 rarely found. They also occur on many kinds of deciduous trees and may be associated with wood-rots in these trees. The perennial fruiting-bodies are produced on the lower part of the trunk and are thick, woody, shell-shaped bodies, measuring from three to six by five to ten inches. The upper surface is marked with numerous concentric ridges. It is straw-colored and slightly hairy or smooth. The under surface is rose-colored at first but becomes darker with age. The pores are small. The inner substance of the fruiting-body is corky and yellowish brown. Cause. The pecky heartwood-rot of bald cypress is caused by Fomes geotropus. The spores from the tubes on the under side of the fruiting-body infect broken branches in the top of the tree. From these points of entrance, the mycelium grows downward into the heartwood. The mycelium becomes abundant in cer- tain centers. At these places the yellow areas appear and finally the pockets are formed. From the first formed yellow areas, strands of the mycelium penetrate the normal wood in all direc- tions without destroying it. At some distance from the original yellow areas, new centers of luxuriant mycelial growth originate and pockets are formed. In this way the wood may become pecky in older trees throughout the entire length of the trunk. Pecky cypress is peculiar in the fungus usually ceasing its activity with the formation of the pockets. The cells imme- diately surrounding the pockets are filled with a brown humus compound, which is believed to inhibit the further development of the mycelium. The wood between the pockets is normal and no further decay takes place when the pecky timber is placed under the various extreme conditions conducive to decay. Normal cypress and pecky cypress timbers are equally resist- ant to decay and are the longest lived of the timbers of this country. | 100 MANUAL OF TREE DISEASES For further details concerning the general life history and control of the wood-rot fungi, see page 64. REFERENCE Schrenk, Hermann von. A disease of Taxodium distichum known as peckiness, also a similar disease of Libocedrus decurrens known as pin-rot. Missouri Bot. Gard. Ann. Rept. 11: 23-77, pls. 1-6. 1900. ‘ CHAPTER IX BASSWOOD DISEASES THE several species of basswood or linden (Tilia) are common in eastern and central United States. These trees, as well as several European basswoods, are extensively used as shade and ornamental trees in the same region. No serious diseases affect the basswood. Several leaf-spots and one powdery mildew affect the leaves occasionally. The sapwood may be destroyed and the trees killed where wood- peckers damage the bark and allow fungi to enter. In the South the roots of the basswood are often decayed by a fungus which is common in heavy soils. PowpErRY MILDEW Caused by Uncinula Clintonii Peck This powdery mildew fungus attacks the leaves of basswood in northeastern and north central United States. The myce- lium is visible on both sides of the leaf, causing diffused powdery white patches. Small black fruiting-bodies which are just visible to the unaided eye are scattered over the whitish area. This species, although indistinguishable from other pow- dery mildew fungi, except by microscopic characters, is so far the only one reported on basswood leaves. The life histories and methods of control of powdery mildew fungi are discussed on page 37. 101 102 MANUAL OF TREE DISEASES LEAF-SporT Caused by Cercospora tilie Peck The leaves of the basswood are often affected by this disease. Large brown dead areas are formed at the tip or along the mar- gin of the leaf (Fig. 10). A broad yellowish border surrounds Fic. 10.— Leaf-spot of basswood. the spot. The fruiting bodies of the causal pathogene are in- conspicuous. For the general life history and control of leaf- spot fungi, see page 30. ‘ BASSWOOD DISEASES 103 WuitrE Sapwoop-Rot Caused by Collybia velutipes Curtis This sapwood-rot is occasionally found in basswood, horse- chestnut and other deciduous trees. The sapwood becomes soft and decayed, and the decline and death of the tree gradually results. Injuries in the bark caused by woodpeckers and other birds are often found to predispose the trees to attack. The sporophores of the causal fungus emerge in clusters from wounds in the bark. They are small toadstools, with yellow or brownish tops and gills. The bases of the stems are coy- ered with a dark brown velvety growth of hairs. For the gen- eral life history and control of the wood-rot fungi, see page 64. REFERENCE Stewart, F.C. Trunk rot. ?Collybia velutipes Curt. (Horse chest- nut). In Notes on New York plant diseases, 1. New York Agr. Exp. Sta. Bul. 328: 361. 1910. SOUTHERN Root-Rot Caused by Ozonium sp. A great variety of plants in the South, including many trees, are attacked by a root parasite, which is peculiar in that no spores of any type have been found and it is known only by the mycelium. Cotton and sweet potatoes are among the field crops seriously affected. Several kinds of trees, especially bass- wood, elm, cottonwood (poplars) and mulberry, are known to be attacked and the roots killed. Plum trees and closely re- lated species and varieties are more or less immune. The second- ary symptoms are those which accompany any root-rot. The leaves wilt and die when the roots are no longer able to function in furnishing sufficient water and food materials. The roots are invaded by the mycelium and the living tissues are killed. 104 MANUAL OF TREE DISEASES Abundant growths of the sterile mycelium, which is coarse, loosely matted and reddish brown, cover the affected roots. It also grows over decaying sticks and other matter on the surface of the ground. The mycelial growth has the appearance of a quantity of tangled hair. The mycelium spreads through the soil and is transported in various ways by cultivating tools. It is said to display excep- tionally destructive tendenciés in wet, badly drained soils and during rainy periods. Loosening the soil, deep plowing and drainage are said to reduce losses by retarding the spread of the mycelium in the soil. REFERENCE Galloway, B. T., and Woods, A. F. Southern root-rot. Jn Diseases of shade and ornamental trees. U.S. Dept. Agr. Yearbook 1896: 248-249. 1897. CHAPTER X BEECH DISEASES THE beech (Fagus) is a common tree throughout eastern and central United States. The American and different varieties of the European beech are often used as ornamentals. No serious diseases of the leaves of beech are known. Several fungi cause leaf-spots occasionally and a sooty mold fungus often occurs on the leaves (see pages 27 and 41). The beech is subject, however, to several wood-rot diseases. The yellowish sapwood-rot and common white wood-rot are very destructive in the forest. The roots are parasitized by the flowering plant commonly known as beech-drop. This parasite, however, does not cause any damage. YELLOWISH SAPWooD-RoT Caused by Fomes fomentarius Fries This sapwood-rot is common on beech, yellow birch and to a lesser extent on other deciduous trees of northeastern and north central United States. The fungus causing the decay is also an important and rapid timber-destroyer throughout its range. Where beech or birch is predominant and any unusual amount of injury has occurred because of fire or limb breakage, this sapwood-rot is found in great abundance and causes large losses in timber values. It is also a common disease in Europe. Symptoms. The decay produced is distinctly a sapwood-rot at first, starting in the outer layers next to the bark. As a result of ; 105 106 MANUAL OF TREE DISEASES the activities of the fungus, the wood is reduced to a soft, light yellowish punk. Black lines are formed between the decayed and unaffected wood in places, or they may persist in the com- pletely decayed portion. The rot extends into the heartwood toward the center of the tree. Where splits or checks occur in the decayed portion, a chamois- like sheet of closely woven yel- lowish mycelium is formed which fills the space and can with care be removed in large pieces. Trees are usually first affected in the upper half. The sporophores or punks of this fungus, which are formed on the trunks of affected trees, usually occur in large numbers on each tree, the number vary- ing with the extent of the de- cay. The sporophores are not confined to old branch wounds as usually is the case with heartwood-rotting fungi, but emerge from apparently unin- jured bark of the trunk. They are easily recognized, being dis- tinctly hoof-shaped and light to dark gray on top. The lower surface is light brown, with rather large regularly arranged circular pores. Both surfaces are smooth and velvety when young. A new layer of tubes is added each year, which extends beyond the previous year’s growth, producing an arched ridge (Fig. 11). The margin of the sporophore is rather thin and the tube-surface is some- what concave. Fig. 11.— Fruiting-body of Fomes fomentarius. BEECH DISEASES 107 Cause. The common yellowish sapwood-rot of beech and yellow birch is caused by Fomes fomentarius. Spores drop out of the tubes on the under side of the sporophores and are blown away. Any wound in the bark exposing the sapwood furnishes a suitable place for these spores to germinate and start a new mycelium. The elements of the wood are largely destroyed, leaving a loose mass of easily crumbled fibers. The effect of such a sapwood- rot on the life of the tree is more serious and quickly destructive than when equally extensive areas of the heartwood are de- stroyed. The decay of the sapwood interferes with the trans- portation of food materials and water, and thus produces the same effect as mechanical girdling. After the tree dies, the fungus works very rapidly as a saprophyte and destroys the re- maining wood. For further details concerning the life history and control of the wood-rotting fungi of living trees, see page 64. REFERENCE Schrenk, Hermann von, and Spaulding, P. Decay caused by Fomes fomentarius. Jn Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 50-51. 1909. Common WuitEeE Woop-Rot Caused by Fomes igniarius Fries This white wood-rot is a common and destructive disease of beech. Many other kinds of deciduous trees are subject to the same disease, principally poplar, oak and maple. In the Adiron- dack Mountains as much as ninety per cent of the second growth is sometimes made worthless for timber by this wood-rot. The decay may extend outward into the sapwood and cause the death of the parts above. The characteristics of the sporophores and the decay are similar for all kinds of trees affected and are de- scribed more fully under poplar diseases, page 305. 108 MANUAL OF TREE DISEASES Unirorm WHITE Sapwoop-Rot Caused by Hydnum septentrionale Fries This sapwood-rot is sometimes found in beech and maple. The affected wood is white, soft and uniformly rotted. Brown zones border the decayed area. § Sometimes. single and double black lines are irregularly distributed in the white rotted wood. Large, heavy, fleshy fruiting-bodies are formed on the side of the tree. A thick sheet of mycelium grows over the bark and from this project numerous small brackets with the under sur- face covered with teeth. The entire structure is white or yel- lowish. For further details concerning this sapwood-rot, see under maple diseases, page 234. Waitt Butt-Ror Caused by Fomes applanatus Fries The heartwood of the roots and base of the trunk of beech is occasionally destroyed by this rot. The decayed wood becomes a little lighter in color than the normal wood. It is solid and when split longitudinally numerous sinuous whitish tunnels are apparent (Fig. 12). The decayed area is bordered by a broad discolored zone. The sporophores of the causal fungus are woody shelf-like bodies with a brownish or gray, smooth upper surface and a white under surface. For further details concern- ing this wood-rot, see under poplar diseases, on page 310. PARASITIZED Roots Caused by Epiphegus virginiana Barton The roots of beech are parasitized by a peculiar flowering plant, beech-drop (Epiphegus virginiana). This plant belongs to the family Orobanchaceee, which comprises about one hun- dred and fifty species, all of which are parasitic on roots of other BEECH DISEASES 109 plants. The beech-drop is confined to America and is found throughout the range of the beech. The plants grow abun- dantly under beech trees in the woods but it is doubtful whether much appreciable damage is done to the tree. In this respect they may be compared with the mycorhizas of tree-roots (see page 82). The — beech- drop plant is much branched, leafless, purplish-brown and stands from four to twelve inches high. Small purplish flowers are borne on_ the stems inracemes. In the soil the stem ends in a white bulb- like or elongate rhizome which is coy- ered with numerous twisted, stiff out- growths known as grapplers. They serve for support and may absorb) water and mineral nutriment. 3 All beech-drop plants, Fig. 12.— Beech wood decayed by Fomes however, if carefully GP Pianonae: dug, will be found to be attached to small beech roots. The tissues of the rhizome of the parasite are fused with those of the beech root so completely that at the point of attach- ment it cannot be definitely recognized to which plant they belong. The beech root is enlarged for some distance each way 110 MANUAL OF TREE DISEASES from the point of attachment and often the end of the parasi- tized root dies, leaving the beech-drop apparently attached to the end of a root. Food material for the development of the beech-drop is drawn from the beech root, and a large amount of starch is formed and stored in the underground rhizome. The entire plant dies during the fall and winter and apparently is propagated as an annual by over-wintering seed. When de- sired, the plants may be eradicated by pulling. This should be done before the seeds are formed so as to prevent a crop the next season. REFERENCE Schrenk, Hermann. Parasitism of Epiphegus virginiana. Amer. Micros. Soc. Proc. 15: 91-128, pls. 1-10. 1894. (Bibliography given.) CHAPTER XI BIRCH DISEASES Many species of birch (Betula) occur as forest-trees in the United States, especially in the northern parts. The native species and imported varieties from Europe and Asia are used extensively as ornamentals. The leaf-rust is destructive when birch and larch are grown close together. The leaf-blister diseases and the several leaf- spot diseases (see page 29) are not common and do very little damage. Birch is, however, commonly affected by several wood-rots, the most important of these being the powdery sapwood-rot and common white wood-rot. The other wood- rots are not so common and are restricted more or less to certain species of birch. Lear-Rust Caused by Melampsoridium betule (Schum.) Arthur The leaves of various species of birch are sometimes affected by this rust disease. It has been found in Massachusetts, New York, Indiana and Washington and, therefore, probably may appear in the northern states wherever birches and the alternate larch hosts occur in proximity to one another. The leaf-rust is not known to cause any great damage. Symptoms. Small, round, reddish-yellow pustules appear on the under sides of the leaves in the summer. Later in the season a second kind of pustule appears on the same leaves. ‘These are lil ie MANUAL OF TREE DISEASES waxy-yellow and finally become brown and almost black. ‘They may be abundant and thickly cover the under side of the leaves. Cause. The rust of birch leaves is caused by Melampsoridium betule. This fungus occurs also in Europe, where it is known that the basidiospores produced from the over-wintering teliospores on the birch leaves cause the infection of the young needles of larch and produce a blister-rust. The stage on larch has been found rarely in this country but very probably exists more generally and has been confused with the other rusts of larch (see page 212). YELLOW LEAF-BLISTER Caused by Magnusiella flava (Farlow) Sadebeck This leaf-blister disease occurs on white and paper birch in northeastern United States. Small light yellow blisters are formed on the leaves. The mycelium of the pathogene enters the tissue of the leaf and causes a stimulus which results in an . increase in number and size of the cells. The increased size of the affected tissue results in the bulging blisters in the leaf. The fungus produces asci containing ascospores on the surface of the blisters. For the control of this disease, the same methods used for peach leaf-curl should give equally good results (Hesler, L. R., and Whetzel, H. H., Manual of fruit diseases, p. 277). Rep LEAF-BLISTER Caused by Ezxoascus bacteriospermus (Johanson) Sadebeck and Ta- phrina carnea Johanson Two species of the leaf-blister fungi are found on Betula nant. The first mentioned has also been found on Betula glandulosa. Although these pathogenes have been described BIRCH DISEASES 113 only briefly from a few collections in northeastern United States, Canada and Greenland, they may be more generally distrib- uted and common on other species of birch. The lesions are confined to the leaves and consist of large reddish brown blistered areas, which may cause the leaf to curl. The mycelium is confined to the space which it makes for itself between the cuticle and the epidermal cells. Due to the parasitic activities of these fungi, the tissues of the leaf are stimulated to an in- crease both in number and size of the cells. This results in the bulging and curling of the leaf between the more rigid veins. For the control of these diseases, the same methods that are used for peach leaf-curl should give results (Hesler, L. R., and Whetzel, H. H., Manual of fruit diseases, p. 277). PowpErRY Sapwoop-Rot Caused by Polyporus betulinus Fries Many species of birch are subject to this sapwood-rot through- out the northern hemisphere. Yellow, white and paper birch are commonly affected in the United States. Although the fungus causing this rot is very common on injured and dead birch trees, its importance in causing serious damage to healthy trees is questioned. The fungus does not enter through branch wounds and other injuries where heartwood is exposed and, therefore, never causes a heartwood-rot of the living tree. This rot is similar to the yellowish sapwood-rot caused by Fomes fomentarius. In the case of both of these fungi, badly injured or weakened trees are attacked and the sapwood is the first part of the trunk decayed. Later, the fungi extend their activities into the heartwood and the entire woody cylinder of the trunk is destroyed. These wood-rots are nevertheless important in the forest since the timber value of the species they affect rapidly deteriorates as soon as the trees become mature or injured. I 114 MANUAL OF TREE DISEASES Symptoms. The decayed wood is yellowish and cracks radially and tangen- tially. The rot is uniform and in the final stages it is very light in weight and easily crushed to a powder. The sporophores of the causal fungus are very common on birch. They are corky annual bodies and are quickly destroyed by insects. From the point of attachment to the trunk, they Fig. 13.— Fruiting-body of Polyporus betulinus. hang as bell-shaped bodies varying from three to ten or more inches across. The outer surface of the sporophore is smooth and light to dark mottled gray in color (Fig. 13). The margin is incurved and projects below the under surface. The lower surface is white or yellowish and roughened by ragged projec- tions. The pores are small and the entire layer of tubes separates easily from the fruiting-body. BIRCH DISEASES 15 Cause. The powdery sapwood-rot of birch is caused by Polyporus betulinus. ‘The spores borne in the tubes on the under side of the sporophore cause infection in wounds where the sapwood isexposed. For a fuller discussion of the life history and control of wood-rot fungi, see page 64. REFERENCES Sehrenk, Hermann von, and Spaulding, P. Decay caused by Poly- porus betulinus. Jn Diseases of deciduous forest trees. U. S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 51-52, pl. 9. 1909. Mayr, H. Zwei Parasiten der Birke, Polyporus betulinus, Bull., and Polyporus levigatus, Fries. Bot. Centralbl. 19: 22-29, 51- 57, pl. 1-2. 1884. YELLOWISH SAPWooD-RotT Caused by Fomes fomeniarius Fries Yellow birch and beech are commonly affected by this sap- wood-rot. Other kinds of deciduous trees are sometimes attacked. The sporophores are perennial, light or dark gray above, smooth and hoof-shaped with a concave, brown, velvety tube-layer. The sapwood is decayed and only an easily crumbled mass of fibers is left. A more complete description of the symptoms of this wood-rot is given under beech diseases, page 105. Common WuitE Woop-Rot Caused by Fomes igniarius Fries The common and destructive white wood-rot of poplar, beech, oak, maple and other deciduous trees affects the yellow and paper birch. Although not as prevalent on birch as on many other kinds of trees, it is often found, especially when the birches are growing in mixture with the more susceptible 116 MANUAL OF TREE DISEASES host species. The characteristics of the rot and the sporophores of the causal fungus are described under poplar diseases, page 305. The hoof-shaped type of sporophore is more common on birch. The sapwood of birch is invaded and the trees die. For a general discussion of the life history, dissemination of the. spores, mode of infection and control of the wood-rotting fungi, see page 64. Brown HeEArtTwoop-Rot Caused by Fomes fulvus Fries This heartwood-rot has been found common in river birch in Missouri and Arkansas. Other trees are affected by the same rot, especially species of Prunus. It is common also in fruit-trees of the genus Prunus and in the olive in Europe. But little information is available on the rot as it occurs in this country. The decayed wood is brown for several feet upward and downward from the point where the sporophores are formed. In the final stages of the decay the rotted wood crumbles easily. Plate-like sheets of mycelium which are common in the brown checked wood-rot are lacking in the case of this disease. The sporophores are formed at wounds. They are perennial, hard, woody and more or less hoof-shaped. The tops of the older sporophores are smooth and very hard. Fine concentric fissures are present but the top does not become roughened. The lower surface is reddish brown and covered with minute pores. For the general life history and control of wood-rotting fungi, see page 64. REFERENCE Schrenk, Hermann von, and Spaulding, P. Red heart-rot of birch caused by Fomes fulvus. Jn Diseases of deciduous forest trees. U. 8. Dept. Agr. Bur. Pl. Ind. Bul. 149: 47. 1909. BIRCH DISEASES iS Ly/ WuitE Butt-Ror Caused by Fomes applanatus Fries The heartwood of the base of the trunk and the roots of birch is sometimes destroyed by this rot. The decayed wood is marked by numerous sinuous, white-stuffed tunnels which run in the horizontal direction (see Fig. 12, page 109). The sporo- phores of the causal fungus are woody, shelf-like bodies with a brownish, smooth upper surface and a white under surface. This heartwood-rot is more fully described under poplar diseases, on page 310. CHAPTER XII BUCKEYE DISEASES Tue four species of buckeye or A‘sculus native in the United States are not important forest-trees. The Ohio and yellow buckeye grow to be large trees in the river-bottom lands in the central and southern states. A closely related European species, the horse-chestnut, is extensively used as an orna- mental. Leaf-blotch is the most destructive disease affecting buckeye and horse-chestnut. This disease occurs every year through- out the range of the Ohio and yellow buckeye. The horse- chestnut is often severely affected and defoliated in the north- eastern states. A powdery mildew is also common on these trees. The California buckeye is subject to a leaf-blight and witches’-broom disease. ‘The wood and roots of the buckeye are rarely diseased. LEAF-BLoTCH Caused by Guignardia esculi (Peck) Stewart Throughout central, southern and eastern United States, Ohio and yellow buckeye and the horse-chestnut are commonly affected by this leaf-blotch. The disease is also known in southern Europe. It is probable that the disease is present to some extent on the other species of buckeye. A large percentage of the foliage of horse-chestnut trees in parks and along streets is affected every year. In the nursery this disease interferes seriously with the growing of horse-chestnut stock. Repeated 118 BUCKEYE DISEASES 119 defoliation results in retarding the growth of the trees and making them more susceptible to winter-injury. Symptoms. The lesions develop on the leaflets and petiole. When first evident, the spots are irregular in outline, slightly dis- colored and water-soaked in appearance. Later the center of the spot becomes red- dish brown and is sur- rounded by a_ yellowish zone which blends into the green of the healthy part of the leaf. Finally, the entire affected area turns brown and becomes dried and brittle (Fig. 14). The spots may be small or may involve large areas and cause a curling of the leaflet. Small black specks, the fruiting-bodies of the pathogene, develop either in the lighter colored center of the brown blotch or may be found distrib- uted sparingly over the entire dead area. Small reddish brown lesions are also sometimes formed on the petioles. Fig. 14.— Leaf-blotch of horse-chestnut. Cause. The leaf-blotch of horse-chestnut and buckeye is caused by the fungus Guignardia e@sculi. Fruiting-bodies containing 120 MANUAL OF TREE DISEASES ascospores are formed in the dead leaves after they fall to the ground. ‘These spores mature at about the time the new leaves appear in the spring and are disseminated by the wind and spattering drops of rain. The lower leaves of young trees and sometimes of older ones are the first to show infections in the spring, because they are closer to the source of spore-production. The first lesions soon develop the other type of fruiting-bodies on the dead areas mentioned above. These appear as minute black dots. In this stage the fungus is known as Phyllosticta spheropsoidea. The spores are extruded from the fruiting- body and are mainly distributed to healthy foliage by wind and rain. By repeated generations of this kind of spores, all the leaves on a tree may become infected in a short time. Con- tinued or periodically rainy seasons are especially favorable for an epiphytotic, since moisture conditions necessary for germina- tion are furnished for each new crop of spores. At such times the foliage from a distance appears as if scorched by fire and considerable defoliation may result. Control of leaf-blotch. In the nursery it has proved beneficial, in preventing to some extent the amount of primary infection, to plow under or rake together and burn all dead leaves around the trees. This practice can be. applied to shade-trees and thus eliminate to a large degree the source of early infections. Even when such measures are taken, a slight amount of infection may result from bits of leaves left on the ground or from early infections on trees in the vicinity. It is, therefore, necessary to supplement these measures by coating the leaves with some efficient fungicide at the time weather conditions and the development of the leaves are conducive to infection. Spraying with lime-sul- fur (1-50) or bordeaux mixture (5—5-50) will prevent infection. The foliage is so dense, however, that thorough spraying cannot be done without drenching the foliage. This may lead to BUCKEYE DISEASES 121 unsatisfactory results for two reasons: spray mixtures do not act as efficiently if the foliage is drenched, and lime-sulfur may cause burning. Dusting nursery trees with a mixture of finely ground sulfur and powdered arsenate of lead, in the pro- portion of ninety parts of sulfur to ten of lead powder, has proved effective in controlling this disease. It may, therefore, be assumed that dusting shade and ornamental trees will be equally effective. For further directions on spraying and dusting for the control of leaf-diseases, see page 357. REFERENCES Stewart, V. B. The leaf blotch of horse-chestnut. Cornell Univ. Agr. Exp. Sta. Bul. 371: 411-419, pl. 10, figs. 85-92. 1916. Stewart, V. B. The leaf blotch disease of horse-chestnut. Phyto- pathology 6: 5-19, pls. 2-4, fig. 1. 1916. PowpEerY MILpEWw Caused by Uncinula flerwosa Peck The leaves of the buckeye and horse-chestnut are affected by a powdery mildew, in eastern, southern and central United States. The powdery white mycelium usually occurs only on the under surface of the leaf in diffused spots. The black fruiting-bodies of the fungus are just visible to the unaided eye and are found scattered over the mildewed areas late in the summer. For a discussion of the general life history and methods of control of powdery mildew fungi, see page 37. CurLED LEAr-BLiGHT AND WrtTcHEs’-BROoM Caused by Exoascus esculi (Ell. and Ev.) Patterson This disease is described on the California buckeye. It occurs in several localities in California. The most noticeable symptom is the production of many large witches’-brooms. The leaves which are borne on the twigs composing the broom [22 MANUAL OF TREE DISEASES are killed before they mature and appear as frost-injured. The mycelium is perennial in the twigs. The leaves of the normal branches also become spotted and curled. Small yellowish blisters. are formed which later turn to a dull red. The fungus causing this disease is a close relative of the leaf- blister fungus on oak (see page 239). Thedisease on the buckeye does not cause very much damage to the trees, since the leaves naturally remain on the tree only from April to early summer. REFERENCE Harkness, H. W. The eurled leaf (Ascomyces deformans). Zoe 1: 87-88. 1890. Wuitr Sapwoop-Ror Caused by Collybia velutipes Curtis The sapwood of horse-chestnut is sometimes destroyed by this toadstool. The wood becomes whitish and soft. The spores of the fungus find entrance through wounds in the bark. The fruiting-bodies of the causal fungus are toadstools with yellow or brownish tops and gills. The bases of the stalks are covered with a brown or black velvety growth of hairs. A fuller discussion of this disease will be found under basswood diseases, on page 103. CHAPTER XIII BUTTERNUT DISEASES Tue butternut (Juglans cinerea) throughout its range in eastern and central United States is subject to a few diseases only. The most important of these is the leaf-spot, which also affects walnut and hickory. This disease often causes a part or all of the leaves to fall from the tree in midsummer. Oc- easionally the brown checked wood-rot and common white wood-rot are found in butter- nut. LEAF-SPOT Caused by Marssonia juglandis (Lib.) P. Magnus This is the common leaf- spot of butternut and walnut. Irregular dark brown spots ap- pear on the leaflets in early summer. When infection is abundant, a large amount of the leaf-tissue is killed and the leaves fall from the tree. The illustration shows a single leaflet affected by this disease (Fig. 15). The parasitic fungus causing the spots forms inconspicuous 123 Fig. 15.— Leaf-spot of butternut. 124 MANUAL OF TREE DISEASES fruiting-structures on the under sides of the dead areas. Spores from these structures are produced in abundance during wet weather and are disseminated by rain. After the leaves fall, perithecia are formed and from these ascospores are available in the spring for primary infection. The name applied to the perithecial stage is Gnomonia leptostyla (Fries) Ces. and De Not. For a further discussion of leaf-spots and their control, see page 27. Common Wuite Woop-Rot Caused by Fomes igniarius Fries The butternut is sometimes affected by the common white wood-rot, which occurs in many kinds of deciduous trees, especially poplar, beech, oak and maple. The sporophores of the fungus and the characteristics of the rot are similar for all the kinds of trees affected and are described under poplar diseases, page 305. Brown CueckeD Woop-Rot Caused by Polyporus sulphureus Fries Butternut is occasionally affected by the brown checked wood-rot, caused by the sulfur fungus. Many other kinds of trees are affected by the same disease. The sulfur-yellow, annual fruiting-bodies of the fungus together with the brown powdery character of the rotted wood make it easy to identify this disease. The tops of trees and large limbs may be killed by the invasion of the sapwood and bark. A more complete discussion of this wood-rot will be found under oak diseases, page 247. / CHAPTER XIV CATALPA DISEASES THE two species of catalpa grow naturally in southeastern and central United States. Both species are used as orna- mentals. A few leaf-spot diseases cause some damage to catalpa according to the locality and the season (see page 30). Otherwise the tree is not subject to serious diseases, except in plantations where the yellow wood-rot is destructive. The predisposing of the catalpa to this wood-rot, by planting the trees closely, illustrates the importance of branch wounds as infection courts for the heartwood-rotting fungi. The rapidity with which this rot progresses in the living tree com- pared with the well-known durability of catalpa timber points to the existence of some condition within the tree which favors the development of the causal fungus. YELLOWISH Woop-Rot Caused by Polystictus versicolor Fries This destructive heartwood-rot of the hardy catalpa may be found wherever the trees grow. The disease is not common in trees growing in the open. In close stands, however, the limbs are killed by shading and after they break away, holes are left which soon become infected by the spores of the fungus causing this rot. The causal fungus is a very common sapro- phyte, which grows everywhere on the wood of deciduous trees. It may often occur as a semi-parasite in the bark and 125 126 MANUAL OF TREE DISEASES sapwood of deciduous trees when they have been severely injured. Otherwise the catalpa is the only tree in which this fungus is known. to cause a distinctive heartwood decay. Symptoms. The affected trees may be recognized by the holes in the trunk where the old branch stubs have rotted. Insects and birds remove the decayed wood and use the hollowed-out areas in the trunk for habitations. In cross-sections of the trunk, the first indications of the decay show as pale colored areas. The spring-wood of the annual rings becomes reddish with small whitish areas. Later both the spring- and summer-wood of the annual rings are similarly affected. The decayed wood then becomes straw-yellow and is very soft and brittle. The de- cayed area enlarges rapidly and eventually the sapwood may be invaded. The decay may extend into the branches and roots. Coppice is usually affected if the wood of the stump is decayed. The fruiting-bodies of the causal fungus are formed where the bark is dead or on the affected wood when it is cut from the tree. They are thin, tough shelving structures, hairy on top and marked with variable yellowish and brown shiny zones. The under surface is yellowish or white and covered with small pores. The fruiting-structures are annual bodies but they persist through the winter and may revive and shed spores in the spring. Cause. The yellowish soft wood-rot of hardy catalpa is caused by the fungus Polystictus versicolor. The spores from the tubes on the under surface of the fruiting-bodies are wind-borne and cause infection when they lodge in branch wounds. When the trees are planted close together, the lower shaded branches die and remain attached to the tree for some time. When CATALPA DISEASES 127 they are broken off, a hole is left in the trunk which serves as an excellent infection court. The mycelium progresses rapidly in the wood. For further details concerning the life history and control of the wood-rotting fungi, see page 64. Control. As a means of preventing loss from this rot in plantations, it is advised that the lower limbs should be pruned off and the wounds treated with a dressing. Directions for these opera- tions will be found on page 345. REFERENCES Sehrenk, Hermann von. II Diseases of the hardy ecatalpa. Jn The hardy catalpa. U.S. Dept. Agr. Bur. Forestry Bul. 37 : 49-58, pls. 23-30, figs. 1-2. 1902. Stevens, Neil E. Polystictus versicolor as a wound parasite of eatalpa. Mycologia 4: 263-270, pls. 74-75. 1912. Stevens, Neil E. Wood rots of the hardy catalpa. Phytopathology 2: 114-119, pl. 10. 1912. Brown Butt-Ror Caused by Polyporus (Poria) catalpe Schrenk The heartwood and sapwood of the base of the hardy catalpa is sometimes affected by this brownish wood-rot. The wood becomes reddish brown and crumbly. It cracks along the annual rings and at times across them, leaving spaces which are filled by felts of mycelium. The fruiting-bodies of the causal fungus are described as thin sheets of mycelium which lie closely appressed to the diseased wood. The surface is covered with small pores which are the openings of perpen- dicular tubes in which the spores are borne. The fruiting- structures are at first whitish, but later become yellowish and brown. This fungus enters the tree through the branch wounds in the same way as described under the yellowish wood-rot 128 MANUAL OF TREE DISEASES (see page 125). The control is the same for both of these dis- eases. REFERENCE Schrenk, Hermann von. II Diseases of the hardy catalpa. Jn The hardy catalpa. U. S. Dept. Agv. Bur. Forestry Bul. 37: 49-58, pls. 23-30, figs. 1-2. 1902. CHAPTER XV CEDAR DISEASES Tue white cedar of the Atlantic Coast and incense cedar of the Pacific Coast are affected by several destructive diseases. These two trees belong to different genera (Chameecyparis and Libocedrus). The diseases affecting the white cedar do not occur on the incense cedar and vice versa. They are dis- cussed together in this chapter merely for the convenience of grouping them under the name common to both. The two rust diseases (witches’-broom and branch-swellings) on the white cedar cause serious deformation of the trees and even death when they occur. The incense cedar is also af- fected by a rust-fungus which causes witches’-brooms. ‘The in- cense cedar is subject to a destructive heartwood-rot, which is similar in appearance to the pecky heartwood-rot of bald cypress. The brown felt-blight of incense cedar is important at high altitudes. Eastern LeEar-Rust Caused by Gymnosporangium fraternum Kern The white cedar is sometimes affected by this leaf-rust, along the Atlantic Coast from Massachusetts to New Jersey. No damage is done to the trees. The symptoms are confined to the spore-masses of the pathogene which break through the epidermis of the affected leaves. These spore-masses appear in the spring and are small brown cushion-shaped pustules about an eighth of an inch in diameter. The life history of the causal pathogene is completed on the leaves of chokeberry L 129 130 MANUAL OF TREE DISEASES (Pyrus). The teliospores borne on the brown cushions ger- minate and the basidiospores which are formed in this process are blown away and cause the infection of the chokeberry leaves. Alciospores produced on this host plant then cause infection of the cedar leaves later in the season if they chance to lodge on them. A more detailed explanation of the life history and control of the rust-fungi belonging to the same genus as this pathogene will be found under juniper dis- eases, on page 192. WestTERN LEAF-Rust Caused by Gymnosporangium nootkatensis (Trelease) Arthur Along the Pacific Coast in the Northwest, the yellow cedar is affected by this leaf-rust. The symptoms are similar to the eastern leaf-rust described above. The life history of the causal pathogene is completed on the leaves of species of apple and mountain ash. For a more detailed description of the habits and control of the rust-fungi of this genus, see under eastern leaf-rust, above, and juniper diseases, on page 192. The life history of this rust-fungus differs, however, from all of the other species of the genus Gymnosporangium, in that uredinio- spores are formed on the cedar leaves. The teliospore-cushions have not been found but undoubtedly occur on the cedar leaves associated with the urediniospores. Brown FE.tT-BuicHtT Caused by Herpotrichia nigra Hartig Incense cedar is one of the many conifers subject to this disease in the Northwest. The leaves and twigs are covered with a dark brown mat of mycelium (Fig. 16). The mycelium also enters the leaf-tissues. Young trees and the lower branches of older ones are killed and under conditions favorable for the development of the causal fungus, the trees appear as scorched CEDAR DISEASES iaul by a ground fire. The same disease affects similarly spruce, fir, juniper, arbor-vite and hemlock. It is described under spruce diseases, on page 317. Fic. 16.— Brown felt-blight on incense cedar. EAsTERN WITCHES’-BROOM Caused by Gymnosporangium myricatum (Schw.) Fromme Witches’-brooms are found on white cedar along the At- lantic Coast from Massachusetts to Delaware and in northern Florida and southern Alabama. The witches’-broom and branch-swelling diseases, both caused by similar rust-fungi, 132 MANUAL OF TREE DISEASES are the most important diseases of white cedar. As in the case of the other rust-fungi of cedar and juniper, an alternate host is necessary for the completion of the life history of the fungus. The witches’-brooms are never formed unless bayberry, sweet- fern or wax myrtle shrubs (Myrica) are in close proximity to the cedars. . Symptoms. The infected branches of the cedar become slightly swollen and produce many short laterals which form a compact broom- like growth. In the early spring, orange spore-horns about an eighth or a quarter of an inch long project from the bark of the distorted branches. Cause. The witches’-brooms of white cedar are caused by the rust- fungus, Gymnosporangium myricatum. The life history of this fungus is similar to that of the other cedar and juniper rusts except that the alternate stage is developed on species of Myrica. With this exception the life history described on page 192 will apply in general to this species. Control. Since this rust-fungus requires the presence of both the white cedar and species of Myrica in close proximity in order to carry out its life history, a simple means of protecting the cedars is afforded by destroying the bayberry, sweet-fern or wax myrtle shrubs. If these plants can be eliminated for a distance of several hundred feet or a mile from the white cedars, no further exchange of spores will be likely and the cedars will be safe from infection. REFERENCES Harshberger, J. W. Two fungous diseases of the white cedar. Proc. Aead. Nat. Sei. Phila. 1902: 461-504. 1902. Fromme, F. D. A new Gymnosporangial connection. Mycologia 6: 226-230. 1914. CEDAR DISEASES 133 WESTERN Twic-BLicHt AND WircHEs’-BRoomM Caused by Gymnosporangium Blasdaleanum (Diet. and Holw.) Kern The incense cedar is attacked by this rust disease and con- siderable damage is caused in some regions. The other trees attacked by the same rust, in the other stage of its life history, are cultivated apple, pear, quince, mountain ash and wild species of apple, haw and service-berry. It is most destruc- tive on the cultivated pear. The relation between the stages of this fungus on the two types of hosts, one the incense cedar and the other the plants of the apple family, is explained on page 192, where the life history of these rusts is discussed. Symptoms. Two different effects are produced by this rust. When the smaller twigs are infected, the first symptoms in early spring are the small reddish brown spore-cushions which appear on the surface of the scale-like leaves. During rainy weather these cushions gelatinize and coalesce, forming yellowish masses over the leaves. The leaves of the infected twig then turn yellow and the twig dies. When larger branches are infected, dense clusters of upright branches are produced. The fungus fruits in the manner described above on the younger twigs of the brooms and the twigs are killed. Most of the damage caused by this rust on the incense cedar is due to the development of the witches’- brooms which at times seriously deform the tree. Cause. The twig-blight and witches’-broom of incense cedar are caused by. the rust-fungus, Gymnosporangium Blasdaleanum. The teliospores formed on the spore-cushions on the cedar ger- minate and produce basidiospores, which when blown to the 134 MANUAL OF TREE DISEASES apple host cause infection of the leaves. The zeciospores formed sometime later infect the cedar leaves in the summer and au- tumn. The fungus over-winters as mycelium in the cedar leaves. Further details concerning the life history of rusts of this type will be found under juniper diseases, on page 192. REFERENCES Jackson, H. S. A Pacific Coast rust attacking pear, quince, ete. Second Biennial Crop Pest and Horticultural Report (Oregon Agr. Exp. Sta.) 1913-1914: 204-212. 1915. Jackson, H. S. A new pomaceous rust of economic importance, Gymnosporangium Blasdaleanum. Phytopathology 4: 261-269, pls. 12-13. 1914. BRANCH-SWELLING Caused by Gymnosporangium botryapites (Sehw.) Kern The white cedar on the Atlantic Coast from Massachusetts | to New Jersey and Pennsylvania and in southern Alabama is often affected by this disease. The branch-swelling and witches’-broom diseases of white cedar are the most serious to this tree. Because, however, of the peculiar life history of the rust-fungi which cause them, they are not generally prevalent. The spores formed on the cedar branch-swellings cause the infection of the leaves of the service-berry and an- other type of spores formed on these leaves in turn causes infection of the branches of the white cedar. Thus it is seen that this fungus cannot exist unless the service-berry is in close proximity to the cedars. Symptoms. The infected branches become swollen to two or three times the normal size. The swellings are spindle-shaped and may be several inches long. In the spring, brown pustules about an eighth by a quarter of an inch burst through the bark of the CEDAR DISEASES 135 swellings. These pustules become gelatinous and sometimes may become confluent. Cause. The branch-swellings of white cedar are caused by the rust- fungus, Gymnosporangium botryapites. The teliospores pro- duced on the brown pustules on the cedar bark germinate and form basidiospores which are innocuous to the cedar and can infect only the leaves of the common service-berry. Here, after a few weeks’ growth, eciospores are formed which, if they find their way to the white cedar, cause the infection of the branches and the swellings result after a year or two. For further details concerning the life history of this type of rust, see page 192. Control. Since the fungus can only exist in a region where the white cedar and service-berry stand within a relatively short distance of each other, the eradication of the service-berry serves as a simple method of control. A separation of these two kinds of trees by a few hundred feet may prove effective, although for similar rusts of the juniper, a mile has been found to be a more desirable distance. REFERENCE Harshberger, J. W. Two fungous diseases of the white cedar. Proc. Acad. Nat. Sci. Phila. 1902 : 461-504. 1902. Precky Hrartwoop-Rot Caused by Polyporus amarus Hedgecock The heartwood-rot of incense cedar, known as pin-rot, pecki- ness, dry-rot or pin-disease, does great damage to this tree in California and Oregon. All of the trees in a given area are sometimes found to be affected, the middle portion of the 136 MANUAL OF TREE DISEASES trunk being most often decayed. ‘Trees less than one or two feet in diameter are not usually attacked. Symptoms. The appearance of the affected wood is very similar to the pecky heartwood-rot of cypress (see page 97). Long lens- shaped pockets are formed parallel with the grain of the wood. The pockets are filled with a brittle brown mass of decayed wood. The surface of the pockets is smooth and the wood immediately surrounding is sound. The first evidence of the decay is the darkened color of certain areas varying from one to ten inches long and from one-fourth to one inch wide. The affected wood in these areas is quickly reduced to a brown charcoal-like mass. The pockets vary in arrangement and number much as in the pecky heartwood-rot of cypress, and a similar brown humus-like powder is found in the cells around the margin. The sporophores of the causal fungus are hoof- or bell-shaped bodies appearing at knot-holes in affected trees. They are large bodies, several inches across, soft and spongy when young and later becoming tough and chalky. The upper surface is at-first light brown in color but soon becomes darker brown, especially around the margin. The under surface is yellow or yellow-green and turns brown with age. The pores are small. The fruiting-bodies are soon destroyed by insects. Cause. The pecky heartwood-rot of incense cedar has been showr. to be associated with the fruiting-bodies of the polypore, named Polyporus amarus. This fungus was previously called Poly- porus Libocedrus von Schrenk. The spores borne in the tubes on the under surface of the fruiting-body cause infection of the heartwood of the cedar at branch wounds. The sapwood is not affected. For the details of the general life history and control of wood-rots, see page 64, CEDAR DISEASES 137 The pecky rots of incense cedar and cypress are, as pointed out above, very similar in many respects but are now known to be caused by different species of fungi. REFERENCES Schrenk, Hermann von. A disease of Taxodium distichum known as peckiness, also a similar disease of Libocedrus decurrens known as pin-rot. Missouri Bot. Gard. Rept. 11: 28-77, pls. 1-6. 1900. Hedgeock, G. G. A new polypore on incense cedar. Mycologia 2: 155-156. 1910. CHAPTER XVI CHESTNUT DISEASES Tue chestnut was until recently one of the important forest- trees of New York, Connecticut, Pennsylvania and the Alle- ghany Mountain region southward to’ Alabama. Besides its commercial value as timber, the chestnut was important also in its natural range as a much-favored ornamental. As an orchard-tree, the varieties of the American and foreign species are of relatively less importance. Fifteen years ago the chestnut was not subject to any very destructive diseases. With the appearance of the Endothia canker or blight, however, the very existence of the species seemed threatened. During the first ten years of the spread of the fungus causing this disease, all the chestnut trees over hundreds of square miles were killed. The disease is now prevalent over practically the entire range of the chestnut and apparently only a negligible number will escape destruction. Itis unusual fora parasite to beso adapted that all the individuals are equally susceptible to its attack. Many limiting factors of resistance, temperature, moisture, seasonal conditions, dis- seminating agents and the like serve to hold parasitic fungi in check. The fungus causing the canker, however, is the extreme example of an introduced parasite which is perfectly adapted to the host and the environmental conditions of eastern United States. With the passing of the chestnut, it is scarcely necessary to consider other less important diseases of this tree. Several leaf-spot diseases are common on chestnut. In the North 138 CHESTNUT DISEASES 139 the one caused by Septoria ochroleuca is important. The large leaf-spot is common in the South. Powdery mildews are also common on chestnut leaves. The wood of the trunk is decayed by several fungi and the shoe-string root-rot is very destructive to chestnut (see page 78). LarGeE LEAF-SPOT Caused by Monochetia Desmazierii Sace. Chestnut leaves are commonly affected by leaf-spot diseases. The one here designated as the large leaf-spot is known to occur in the southern Appalachian region in Virginia, North Carolina and Georgia. It is often abundant, and causes some damage by decreasing the functioning leaf-surface. Red oak leaves are affected by the same disease. Symptoms. The symptoms are similar on the chestnut and red oak. Small circular spots appear which are a quarter to one-half inch in diameter, with a pale center and darker surrounding zones, varying in color from yellow and gray to red-brown. These spots enlarge rapidly and sometimes extend entirely across the width of the leaf. Two or three such spots cause the death of most of the leaf-tissue. The bands of colors as described above are present in the older and larger spots. On the under side of the leaf there is less evidence of the colored zones and superficial mycelium of the fungus at the margin of the spot causes a mildewed appearance. Early in the develop- ment of the spots, numerous densely crowded black dots appear on the dead leaf-tissue. Cause. Large leaf-spot of chestnut and red oak is caused by the conidial stage of a fungus known as Monochetia Desmazierit. 140 MANUAL OF TREE DISEASES But little is known of the life history of this parasite. The spores produced in the black dot-like fruiting-bodies on the spots have been proved to infect other healthy chestnut leaves. In this way the fungus is probably disseminated by the rain washing and spattering the spores. A perithecial stage of the fungus is probably developed in the dead leaves on the ground from which primary infection may be brought about in the spring. This point is, however, undetermined. Control. Apparently no attempts have been made to control this disease. General suggestions for the control of leaf-spot dis- eases are given on page 33 and may be of some application to this disease. REFERENCE Graves, A. H. The large leaf spot of chestnut and oak. Mycologia 4: 170-174, pl. 69, fig. 1. 1912. Twic-BLIGHT Caused by Spheropsis malorum Berkeley (= Physalospora cydonie Arnaud) This twig-blight is more common and destructive on chestnut oak. It occurs occasionally on chestnut in central eastern United States. Cankers are formed on the small branches and twigs. The leaves wilt and turn brown in midsummer. A fuller description of this disease and its control will be found under oak diseases, on page 244. ENDOTHIA CANKER Caused by Endothia parasitica (Murr.) Ander. and Ander. All the species of the genus Castanea are susceptible to this destructive fungus. The trees included in this group are: the common American chestnut, the eastern chinquapin, the CHESTNUT DISEASES 141 European and the Japanese chestnut and the western chin- quapin (genus Castanopsis). Pure strains of the Japanese varieties are resistant while all the other species are very sus- ceptible. From an economic standpoint, the American chest- nut is by far the most important species. The Endothia canker has also been known by the common names, chestnut-blight and chestnut bark-disease. It was first noticed in the New York Zoological Park in 1904. Since that time it has spread for hundreds of miles, north, west and south. It has proved to be the most destructive and rapidly spreading tree disease known. The areas which have been swept by the epiphytotic so far, are left apparently without a single living chestnut tree. After many years of speculation as to the past history of this disease, it was discovered in northern China in 1913 and later in Japan. It is of slight importance in its native home. There is little doubt now that the Japanese chestnuts imported into this country brought with them this unnoticed disease of the Orient. The increased destructiveness of the disease in this country is due to the greater susceptibility of the American chestnut. Many examples of epiphytotics due to newly imported pathogenes are now a matter of record and make the regulation of the interchange of plant products one of the important phases of plant disease control. Symptoms. The tissues of the bark, including the cambium, are invaded and killed. ‘The dead areas of bark, or cankers, are especially conspicuous on the younger limbs where the normal bark is smooth and green. They may be seen at a distance because of the reddish color of the dead bark in contrast to the healthy green bark. Usually the cankered area is slightly sunken, due to the killing and drying of the tissues. On young rapidly growing coppice, however, swollen areas (hypertrophy cankers) with the bark split open lengthwise are commonly found. Dur- 142 MANUAL OF TREE DISEASES ing midsummer the cankers enlarge at the rate of about one- half inch in diameter each week. The usual shape of the canker Fic. 17.— Endothia canker of chestnut. is ellipsoidal (Fig. 17). The margin of the canker is usually regular and some- what raised. On smooth bark, the thin cork-layer is wrinkled, forming concen- tric rings about the central point of the canker. As the canker becomes larger, the bark splits and after a time falls away in shreds, leaving the wood bare. When the fungus is working in the living tissues under the rough bark, there are no outward indications of its pres- ence until the fruiting-structures are pro- duced in crevices of the bark. If the bark is peeled from the edge of a canker, the tawny mycelial fans are readily seen (Fig. 18). The invaded tissues are changed to a light brown in contrast to the normal light colored healthy tissue of the bark. The thick bark is reduced to a mass of shreds which are a uniform dark brown. The first layers of wood under the cankered areas also become brown. The effects of the disease on the general appearance of the tree are most noticeable during the summer when the trees are in leaf. In localities in which the disease is common, large numbers of the newly affected branches and twigs are girdled by the cankers during the late summer and the brown shriveled leaves hang to the limbs. This most striking CHESTNUT DISEASES 143 symptom is common in July and August. The dead leaves remain clinging to the limbs during the winter. If the girdling of the limb is completed at a time when the burs are matur- ing, these also remain on the tree over winter. In case the girdling of the limb takes place in late autumn or early spring, after the leaves and burs are shed, the new leaves never attain their full size but remain pale green and distorted. This is a common symp- tom in May and June. Cankers on the trunk, es- pecially if at the base, cause the development of clumps of water- sprouts or suckers below the can- kered area. Such clumps of suckers do not constitute infallible signs of the Endothia canker, however, since girdling caused by any agency will re- sult in such out- growths. After a tree has become thoroughly diseased — and this may take only three or four years after the first ap- pearance in the top of the tree — the brown fruiting-pustules of the fungus cover the dead bark of the trunk and branches, giving the tree a distinctive red-brown hue. The fungus con- tinues to live saprophytically on the dead bark, as long as any remains. Fic. 18.— Mycelial fans between the bark and wood. 144 MANUAL OF TREE DISEASES Cause of Endothia canker. The canker of chestnut is caused by the perithecium-forming fungus E’ndothia parasitica, formerly called Diaporthe parasitica. The mycelium may grow parasitically in the bark, cambium and sapwood of all parts of the chestnut tree above ground or saprophytically on bark, twigs and dead parts of chestnut and other trees. In the northern states new cankers may originate at any time of the year from March to October. The dissemination of the fungus to healthy trees or healthy parts of the same tree is accomplished by many different agencies. The spores or the mycelium itself may be carried by the wind, water, birds, quadrupeds, insects and often by man. The spores and mycelium live through the winter uninjured and are ready for dissemination in the spring when many primary infections are started. The agency most largely concerned in the rapid spread of this fungus from tree to tree is the wind, while water is important in washing the spores from a canker in the top of a tree to other parts of the same tree and to others close by. A few of the millions of spores produced on a single canker find lodgment on the bark of other chestnut trees after a shorter or longer journey from the place where they were produced. Bringing the spores into contact with the healthy bark is not all that is sufficient, however, for the spores must find a wound of some kind to accomplish infection. The spores germinate during periods of moist weather and the short germ-tubes enter the soft tissue of the bark through the wound. If there is no wound in the cork-layer, the germ-tubes of the spores are unable to penetrate. An abundant growth of my- celium rapidly develops from the germ-tube and in a few days thin fan-like plates composed of thousands of threads of my- celium, growing side by side, push out into the soft tissues of the bark which lie between hard fibrous layers (Fig. 18). The cells are killed a little in advance of the mycelium by certain poisons which are excreted. Therefore, as these mycelial fans CHESTNUT DISEASES 145 grow out from the point of infection in all directions, the tissues of the bark are killed and soon a rapidly enlarging canker be- comes apparent. About a month after infection is accomplished, the surface of the small canker becomes covered with numerous small blisters (Fig. 19). These blisters are produced by balls of mycelium formed under the cork-layer. Within these balls are formed one of the types of spores (the conidia). During moist conditions, following rains, . long, twisted, yellow tendrils are pushed out from the ruptured bark over each blister (Fig. 19). The tendrils are a mass of the very small spores dried into this shape after being squeezed through a small opening. The next rain or dew causes these tendrils to sepa- rate into the thousands of spores in each and they then may be washed or spattered about by the water or carried by animate agents. Any one of these spores germinat- ing where the germ-tube may enter : Be Ohio Fic. 19.— Spore-horns of chest- wounded bark-tissue may initiate rine eanicenetain ue: a new canker. On older and larger cankers, the blisters and yellow tendrils of spores are confined to the margin, while nearer the center, reddish brown pustules of mycelium are pushed out through the bark. They measure when fully developed one-sixteenth of an inch or more in diameter and have numerous papille on the upper surface, each with a black dot in the tip (Fig. 20). Within the brown pustules, buried below the surface of the bark, are formed thirty or more cavities (perithecia), within each of which are produced in great abundance another type L 146 MANUAL OF TREE DISEASES of spore (the ascospores). These spores are confined in small delicate sacs, eight spores in each sac or ascus. During rainy periods, these sacs swell and a certain number are forced up through a tube leading from each cavity to the black mouths at the tips of the papillae. Once out- side, the sacs burst and the eight spores in each are shot into the air where they are carried away by the wind to great distances. It is these wind-blown ascospores which account for the extreme rapidity of spread of this fungus and make certain the infection of all trees in the vicinity. The living tissues of the bark and the cambium are killed and the mycelium enters the first layer or two of the sapwood. The indirect effect, when these tissues are killed entirely around a limb, is the withering and dying of the parts above. The tree is thus killed by the successive girdling of the limbs and finally by cankers developing on the trunk. Control of Endothia canker. Fig. 20.— Perithecial stage of After the chestnut canker had eae a developed into a_ destructive epiphytotic in Connecticut, New York, New Jersey and Penn- sylvania, many investigations were begun to determine the facts with regard to the disease and especially with a view toward its control. A method was proposed of eliminating CHESTNUT DISEASES 147 all diseased trees in spot infections somewhat distant from the generally infested areas and the surrounding of the area already invaded, by a zone from which all chestnut trees were to be cut and removed. Much effort was expended in 1911 and 1912 to locate and map the regions in which this method would be put into effect. Trial areas were located and all diseased trees were cut, the timber peeled and the refuse burned. The enormous effort involved in carrying out such a plan to control the disease seemed far too expensive and the results too prob- lematical to warrant their continuance. Pennsylvania, how- ever, by the appointment of a special commission, attempted to carry out the eradication methods in that state, but discon- tinued the work in 1913 after two years’ trial. Since that time the canker has continued its destruction and is gradually ex- tending its range into the northern limits of the chestnut in the New England states, western New York and Ohio and into the southern Appalachians, threatening the total extinction of the tree. The attempt to control chestnut canker in individual trees, when the expense of surgical methods is warranted, may be successful. By the ordinary methods of canker eradication, the diseased areas may be removed. Especial care is necessary in order completely to remove the fungus. The bark should be cut away at least an inch beyond the apparent edge of the canker and the wood beneath the area of bark thus removed must be chiseled out to a depth of an inch. Coal-tar dressing then should be applied to the exposed wood and bark. After all the cankers are removed, careful watch must be kept for the appearance of new cankers. If the tree is large and has rough bark, the chances of discovering all the diseased areas in time are small. The Japanese varieties are sufficiently resistant, if pure stock and not grafted on American roots, to warrant their use as orchard-trees. The crossing of the Japanese and Chinese with 148 MANUAL OF TREE DISEASES the American chestnut may yield a resistant variety which can be grown with relative immunity to this disease. The advertisements of resistant chestnuts at this time, however, are misleading, since none has been developed. REFERENCES Anderson, P. J., and Rankin, W. H. Endothia canker of. chestnut. Cornell Univ. Agr. Exp. Sta. Bul. 347: 531-618, pls. 36—40, figs. 77-101. 1914. Anderson, P. J., and Babeock, D.C. Field studies on the dissemination and growth of the chestnut tree blight fungus. Pennsylvania Chestnut Tree Blight Com. Bul. 3: 1-32. 1913. . Clinton, G. P. Chestnut bark disease. Connecticut Agr. Exp. Sta. Rept. 36: 359-453, pls. 21-28. 1913. Giddings, N. J. The chestnut bark disease. West Virginia Agr. Exp. Sta. Bul. 187: 209-225, figs. 1-12. 1912. Heald, F. D. The symptoms of chestnut tree blight and a brief de- seription of the blight fungus. Pennsylvania Chestnut Tree Blight Com. Bul. 5: 1-15, pls. 1-16. 1913. ' Metealf, H., and Collins, J. F. The control of the chestnut bark dis- ease. U.S. Dept. Agr. Farmers’ Bul. 467 : 1-24, figs. 1-4. 1911. Rankin, W. H., Field studies on the Endothia canker of chestnut in New York State. Phytopath 4: 233-260, pl. 11, figs. 1-2. 1914. Anonymous. Treatment of ornamental chestnut trees affected with the blight disease. Pennsylvania Chestnut Tree Blight Com. Bul. 2:1-7. 1912. STRUMELLA CANKER Caused by Strumella coryneoidea Sace. and Winter This canker occurs on chestnut but is more destructive on various species of oak. On chestnut the sunken cankers are distinguishable from the Endothia canker or blight, but in general the tree is very similarly affected. The first signs of the developing canker on smooth-barked trees appear as yellow- ish or brownish slightly raised areas around a branch stub. Many black nodules an eighth of an inch in diameter are formed on the surface of the affected bark. When the bark is peeled from the cankers, sheets of pure white or only CHESTNUT DISEASES 149 slightly tan-colored mycelium are exposed. No indications of mycelial fans are found as in the Endothia canker. The cankers soon girdle the trunk and the parts above die. Large elliptical conspicuous cankers with depressed centers surrounded by concentric calluses are also formed on chestnut but not so commonly as on the red and black oak. These cankers and the fungus causing them are described on page 245. Brown CHECKED Woop-Rort Caused by Polyporus sulphureus Fries The heartwood and sapwood of chestnut are often decayed by the sulfur fungus. The same rot is common in oak, maple, walnut, butternut, locust, alder and other trees. The wood is reduced to a red-brown, powdery mass which separates into cubes. The sporophores are conspicuous, annual, orange and sulfur-yellow colored bodies which form at wounds or on the bark where the fungus has decayed the sapwood. The tops of the trees or large limbs may be killed by the girdling action of the mycelium in destroying the sapwood and bark. A fuller description of the symptoms and cause of brown checked wood- rot which are similar for all the trees affected is given under oak diseases, page 247. Straw-CoLorED HEARTWOOD-RotT Caused by Polyporus frondosus Fries This heartwood-rot may be found in the base of the trunks of chestnut. The trees do not become hollow. The advancing decay first shows as long, slender, white streaks. Later the wood becomes tan- or straw-colored and is held together by the less affected medullary-rays. The sporophores of the causal fungus arise from the ground around the affected tree. They are large, fleshy, globose structures with many overlapping 150 MANUAL OF TREE DISEASES shelves borne on branches arising from a single central stalk. For further details concerning this heartwood-rot, see under oak diseases, page 259. Waite Pieep Burtr-Rotr Caused by Polyporus croceus Fries (= P. Pilote Schw.) The heartwood of the base of chestnut and oak is often attacked by this white piped-rot. It is also occasionally found in the tops of the trees. The rot extends into the roots and is one of the most destructive wood-rots of the butts of oak in the Ozark Mountains. This disease has been found in chestnut and oak in various localities in eastern and central United States and probably is generally distributed over this area. When chestnut trees have dead limbs in the top, the decay may be found in the upper portion of the trunk. The coppice method of reproduction of the chestnut is responsible for the prevalence of this rot in the base of the trees. Symptoms. The affected wood is at first brownish and water-soaked. Later white areas appear between the spring- and summer- wood. These areas become larger and the wood between is firm and dark brown. Finally the white areas enlarge and become hollow cavities with white margins. The brown wood between the pockets at this stage is brittle and breaks apart easily into concentric layers. The sporophores of the causal fungus are buff- or orange-colored and are found sometimes on living trees or on fallen trees and old logs. They are soft and watery annual shelf-like bodies, three to six inches across. Cause. The white piped butt-rot of chestnut and oak is caused by Polyporus croceus or Polyporus Pilote. Infection usually CHESTNUT DISEASES 151 occurs at the base of the tree through the connection of the coppice sprouts with the old stumps. For further details concerning the life history of wood-rotting fungi and the nature of the decay process caused by these fungi, see page 64. REFERENCES Long, W. H. Three undescribed heart-rots of hardwood trees, es- pecially of oak. Jour. Agr. Res. 1: 109-128, pls. 7-8. 1913. Schrenk, Hermann von, and Spaulding, P. Piped-rot of oak and chestnut. Jn Diseases of deciduous forest trees. U. S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 39-40, pl. 5. 1909. (Note: The piped-rot of oak described is due to P. Rheades and of chestnut to P. croceus.) CHAPTER XVII ELM DISEASES Fig. 21.— Leaf-spot of elm. 152 Tue elms (Ulmus) are common forest and orna- mental trees east of the Rocky Mountains. They are exceptionally free from specific diseases caused by parasites. Wound-rots and slime-flux are common in the crotches of the large limbs. Chaining is often necessary to prevent split- ting at the crotches. LEAF-SPoT Caused by Gnomonia ulmea (Sace.) Thiim. This is the most com- mon of the leaf-spot dis- eases of elm. In wet seasons, the spots become so abundant that defolia- tion results. The fungus causing this disease usu- ally occurs abundantly ELM DISEASES 153 every season on the leaves in late autumn just before the leaves fall. The first indications of the spots are seen on the upper surface of the leaf. The dead leaf-tissue is grayish, and either scat- tered over the spot or grouped in the center are one or more black pustules (Fig. 21). The under sur- face of the leaf shows no evidence of the spot until later in the season, when brown dead areas appear with a few raised pustules. After the leaves fall to the ground, fruiting-bodies containing ascospores de- velop which are the source of primary infection the following spring. The pyenidia of many species of fungi are found on elm leaves and it is not known which one of these is con- nected with the Gnomonia. For a further discussion of leaf-spots and their con- trol, see page 27. Fic. 22.— Powdery mildew of elm. PowpEery MILpEws Caused by Uncinula macrospora Peck, Microsphera alni (Wallr.) Salmon and Phyllactinia corylea (Pers.) Karst. Three species of the powdery mildew fungi attack the leaves of elms in the United States. In the case of all three species the characteristics, so far as visible to the unaided eye, are 154 MANUAL OF TREE DISEASES similar. The first two species mentioned above occur on both sides of the leaf, while the last usually affects only the under side. The spots are usually not distinct and the mycelium may be only slightly noticeable (Fig. 22). The black fruiting- bodies are formed in patches or scattered over the leaf in all three species but require microscopic examination to determine their specific characters. The life histories and methods of control of the powdery mildew fungi are discussed on page 37. Brown Woop-Rot Caused by Pleurotus ulmarius Bull. The white elm is often affected by this brown wood-rot. The toadstool fruiting-bodies of the causal fungus are commonly seen in the autumn projecting from pruning wounds and crotches between limbs. The heartwood is first affected and later the decay extends into the sapwood. The wood becomes brown and is easily separated into its respective annual rings. The cell-walls of many of the fibers of the wood are destroyed or partially delignified. The sporophores of the fungus are large, fleshy annual struc- tures attached to the wood of the tree by a long and more or less eccentric stalk. The top is convex, smooth, and varies from white to yellow or brown. On the under surface are many radiating gills or pendent plates which are notched at the point of attachment to the stalk. It is on these gills that the spores are formed. REFERENCE Learn, C. D. Studies on Pleurotus ostreatus Jacqu. and Pleurotus ulmarius Bull. Annales Mycol. 10: 542-556, pls. 16-18. 1912. CHAPTER XVIII FIR DISEASES Tue firs are important forest-trees of western and north- eastern United States. The balsam and Fraser fir are the only native species in the East. Several species are common in the . West. The Douglasspruce or fir of western United States is also considered in this chapter for convenience. Many native and exotic species of fir are extensively used as ornamentals through- out the country. The word “fir” is properly restricted to the genus Abies, with erect cones and flattish leaves, and the word “spruce” to the genus Picea with cones mostly becoming pendulous and keeled leaves. The red fir or Douglas spruce is of the genus Pseudotsuga. Fir is particularly subject to diseases of the wood. Many of the wood-rotting fungi which attack fir are also equally de- structive to pine, spruce, larch and hemlock. The root-rots common to conifers also cause considerable damage to fir wherever it grows. In western United States the dwarf mistle- toes seriously deform the fir. Besides these important dis- eases, the fir is occasionally affected by leaf blister-rusts, leaf- cast, rust witches’-broom and the gray mold twig-blight. These diseases are limited in their distribution by various environ- mental and host relations. Lear Buister-Rusts Caused by species of Uredinopsis, Pucciniastrum and Calyptospora Several very similar blister-rust diseases of the needles of fir (Abies and Pseudotsuga) are found in the United States. 155 156 MANUAL OF TREE DISEASES In all these diseases the general symptom is the production from the under surface of the needles in early summer of white bladdery pustules or blisters. Although found rather commonly throughout the range of the firs, none of these diseases is known to cause any great damage. A yellowing of the foliage and defoliation may occur at times. The different species of rust- fungi causing these diseases require certain other kinds of plants on which to complete their life history. In all the species the spores (zciospores) developed in the white blisters on the * fir cause the infection of the other host plant if it is in the close vicinity. On this second host urediniospores are formed in small reddish or yellowish spots in midsummer and in the autumn the teliospores develop either within the epidermal cells or on the outside of the leaf or stem. The teliospores over- winter and germinate in the spring, producing basidiospores which when blown to the fir infect the young needles. Fern rust. The most common and generally prevalent of the blister- rust fungi of fir needles have alternate stages on species of ferns and belong to the genus of fungi known as Uredinopsis. The blister-stage on the fir needles is known as Peridermium balsa- meum Peck and P. pseudo-balsameum (D. and H.) Arthur and Kern. These rusts occur on balsam fir in the northeastern states and on Alpine, grand and noble fir in the Northwest. Recent investigations have shown that these blister-rusts are the alternate stages of five previously recognized species of Uredinopsis on ferns as follows : — U. osmunde Magn. on species of Osmunda ; U. mirabilis (Peck) Magn. on species of Lorinseria and Onoclea ; U. struthiopteridis Strémer on species of Anchistea and Matteuccia ; U. phegopteridis Arthur on species of Phegopteris ; ; U. Atkinsonii Magn. on species of Asplenium and Dryopteris. These rusts are not distinguishable from one another in the ecial stage on the fir needles, and further investigation may FIR DISEASES 157 prove that they should be reduced to one species with racial differences as to the fern hosts preferred. A very similar blister-rust of the second-year needles occurs in the northwestern states on Alpine and grand fir and has been found to be due to Uredinopsis pteridis Weir and Hubert on species of Pteridium. The life history of this species is different from those above mentioned in that the teliospores do not over-winter. The basidiospores form in late summer but the fir needles infected in the autumn do not show the white blisters until early the following spring. In the other species the young newly formed needles are infected in the spring by basidiospores from over-wintered teliospores, and the white blisters are formed later in the same season. On the fern leaves the urediniospores show as yellow or brownish rust-spots. Fireweed rust. Another of the white blister-rusts occurring to some extent on fir needles in this country as well as in Europe is caused by Pucciniastrum pustulatum (Pers.) Dietel. This pathogene has its uredinial and telial stages on species of Epilobium, es- pecially E. angustifolium, the great willow-herb or fireweed. Although the fungus occurs on several species of Epilobium, teliospores are known certainly to occur only on E. angusti- folium. Blueberry rust. A common blister-rust of fir needles in Europe is caused by Calyptospora columnaris (Alb. and Schw.) Kiihn. It has its alternate stages on species of Vaccinium. On these latter plants the stems are attacked and become swollen. The in- fected stems grow erect and become much taller than sur- rounding bushes. The stems are at first reddish and later become brown or black. The teliospores are formed in the 158 MANUAL OF TREE DISEASES epidermal cells of the stems and over-winter there. The germ-tubes bearing basidiospores are pushed out the fol- lowing spring and infection of the fir needles is accomplished when the basidiospores are blown to them. The white blisters appear on the needles in late spring. The affected needles may appear yellowish and usually drop off in late summer. The blister-stage on the fir is known as Peridermium columnare Schmidt and Kuntze. This fungus is common throughout the United States on blueberry but is rarely found on firs. Unconnected rusts. Two blister-rust fungi attacking fir needles (Abies) in north- western United States have been named provisionally Peri- dermium ornamentale Arthur and P. Holwayi Sydow. These two forms may represent only a single species, however, as they are very similar microscopically. The alternate stages of these rusts are as yet unknown. REFERENCES Weir, J. R., and Hubert, E. E. Observations on forest tree rusts. Amer. Jour. Bot. 4: 327-335, figs. 1-2. 1917. Clinton, G. P. Hetercecious rusts of Connecticut having a perider- mium for their ecial stage. Connecticut Agr. Exp. Sta. Ann. Rept. 1907-1908 : 369-396, pls. 25-382. 1908. Arthur, J. C., and Kern, F. D. North American species of Perider- mium. Bul. Torrey Bot. Club 33: 403-438. 1906. Fraser, W. P. Cultures of some hetercecious rusts. Mycologia 3: 67-74. 1911. Fraser, W. P. Cultures of hetercecious rusts. Mycologia 4: 175- 1954 LOU: Fraser, W. P. Further cultures of hetercecious rusts. Mycologia 5: 233-239. 1913. Fraser, W. P. Notes on Uredinopsis mirabilis and other rusts. My- ecologia 6: 25-28. 1914. Hedgecock, G. G. Notes on some western Uredineew which attack forest trees. Mycologia 4: 141-147. 1912. FIR DISEASES 159 Lrear-Rusts Caused by Melampsora arctica Rostrup and M., albertensis Arthur Two species of rust-fungi cause pale yellowish or white pustules on fir needles. These rusts are very similar to the blister-rusts described above except that no bladder-like cov- ering 1s developed over the pustules. Willow rust. Arust of balsam fir needles similar to the blister-rusts above mentioned is found in eastern Canada and may occur in the extreme northeastern part of the United States. This disease is caused by Melampsora arctica Restrup. The uredinial and telial stages are formed on arctic species of willow. The ba- sidicspores are formed in the spring from over-wintering telio- spores and infect the new fir needles. White pustules are preduced on the under surface of the fir needles in. midsummer. Poplar rust. A rust of poplar leaves in northwestern United States and the adjacent parts of Canada has its alternate stage on fir (Pseudotsuga) needles causing white pustules. This fungus is known as Melampsora albertensis Arthur and was previously called Ceoma occidentalis Arthur on Pseudotsuga mucronata. LEaF-Cast Caused by Lophodermium nervisequum Fries The needles of balsam fir are often killed by this disease. Trees of all ages are affected and complete defoliation may result. This is especially true of small trees. The leaves be- come yellow and brown during the summer and autumn. The fruiting-bodies of the causal fungus break through the epi- dermis of the brown needles in long black lines. The spores are mature the following spring and infection may occur during 160 MANUAL OF TREE DISEASES any prolonged wet period until the spores are all disseminated. For further details concerning the leaf-cast diseases of conifers, see page 38. REFERENCE Spaulding, P. Notes upon tree diseases in the eastern states. My- cologia 4: 148-151. 1912. Rust WrtcHeEs’-Broom Caused by Melampsorella elatina (Alb. and Schw.) Arthur This rust disease causes witches’-brooms on various species of fir (Abies) throughout their range in the United States. It also occurs commonly in Canada, Mexico and Europe. The young affected twigs are dwarfed and develop numerous up- right laterals forming a broom-like growth. If the twigs are — infected at a place where no buds are present, only gall-like enlargements of the bark are formed. The fungus grows out into the branches and leaves of the broom. The leaves re- main small and yellowish. There develop in midsummer from the under surface of these dwarfed leaves two rows of white blisters. The leaves then fall, leaving the broom bare during the winter. New growth of the twigs and new infected leaves are formed the following season. In this manner the broom develops for several years and produces a crop of spores each season. The spores (eeciospores) from the fir needles infect species of. Alsine and Cerastium. On these plants very small orange- red or yellowish pustules are formed in late summer. Ure- diniospores are produced in these pustules which may infect other plants of the same species. Teliospores are formed later in whitish or pale reddish spots on the under surface of the leaf. They germinate the following spring producing basidiospores which may infect the fir twigs. The mycelium is perennial in both sorts of hosts. FIR DISEASES 161 Control. This witches’-broom of fir may be controlled by eradicating all sandwort and chickweed (Alsine and Cerastium) from the immediate vicinity of the firs. REFERENCE Hartig, R. Aicidium (Peridermium) elatinum. Jn Text-book of the diseases of trees, pp. 179-182, figs. 109-112. 1894. Gray Moxitp Twic-Buicut Caused by Botrytis cinerea Fries This disease of the current season’s twigs is most important on Douglas fir, although other firs, pine, spruce, larch and hem- lock may be affected. The disease is common in certain lo- ealities in Europe and North America, both in nurseries and in the forest. It has been reported as destructive, especially to Douglas fir in nurseries, forest plantings and to some degree on the older trees, in several countries of Europe. In the forests of northwestern United States it occurs on Douglas fir, grand fir, western larch and western hemlock. It has not as- sumed great importance in any area but causes considerable cumulative damage. Symptoms. The most obvious general symptom of this disease is the withering, curling and dying of young twigs of the season. Seedlings and young trees may be killed. Late in the season black bodies the size of a pin-head are formed on the affected twigs and on the leaves, especially at the base of the season’s growth. The twigs of young pine may be dwarfed, the needles remaining short and the twig becoming twisted. Under moist conditions, a more or less luxuriant mycelial growth occurs, forming a gray mold over the affected leaves and twigs. M 162 MANUAL OF TREE DISEASES Cause. The gray mold twig-blight of conifers is caused by the fungus Botrytis cinerea. The name first given to this fungus on conifers was Botrytis Douglas Tubeuf. In some publications this fungus is erroneously called Sclerotinia Fuckeliana (De Bary) Fuckel, due to a suspected connection of the Botrytis with this ascomycete. Spores are borne in abundance on the gray mold- like growth of mycelium over the affected parts. These spores are wind-disseminated and serve to distribute the fungus dur- ing the summer. ‘The small black, more or less globose bodies formed on the twigs and needles are called sclerotia. They are resting structures composed of mycelium which is rich in re- serve food material and covered by a black rind-tissue of mycelium. The fungus over-winters in this way and many upright branches bearing spores are sent out from the sclerotia in the spring. The mycelium within the needles and twigs causes at first an enlargement of some of the tissues and later their death. Abundant atmospheric moisture is required for the general and destructive distribution of the fungus in a given region. Fogs are conducive to epiphytotics. This is due to atmospheric moisture stimulating an abundant growth of superficial my- celium which is necessary for the formation of the spores. Also these same conditions insure that a larger percentage of the spores can germinate and cause infection. Control. Since the severity of attack is largely dependent on a con- tinuously humid atmosphere, any measures which will lead to a greater circulation of the air will serve in a measure to control this disease. Damp soil and close planting should be avoided for the more susceptible trees. In the nursery and in young plantations weeds and any plants or artificial structures which shade the trees should be removed. FIR DISEASES 163 REFERENCES ON Gray Moup Twic-Buicut Weir, J. R. A Botrytis on conifers in the northwest. Phytopathology 221d, 1912: Smith, R. E. Botrytis and Selerotinia: their relation to certain plant diseases and to each other. Bot. Gaz. 29: 369-407, pls. 1-3, figs. 1-3. 1900. ; Tubeuf, C. F. von. Botrytis Douglasii. Eine neue Krankheit der Douglastanne. Beitriage zur Kenntniss der Baumkrankheiten, pp. 4-8, pl. 1. 1888. MistLeTorE Buri AND WITcHES’-BRooM Caused by Razowmofskya Douglasii (Englem.) Kuntze Douglas fir is seriously damaged in northwestern United States by this species of dwarf mistletoe. The roots of the germinating mistletoe seeds enter the bark through wounds. Swellings of the stem and enormous brooms are formed by the abnormal branching from the affected parts. Burls are pro- duced on the larger limbs and the trunk. The general effect of the deformed growths is a diversion of the growth energies of the trees to these parts. A dwarfing of the tops and a de- creased amount of foliage results. Large trees are not directly killed by the mistletoe infestation, but the trees are suppressed to the degree that insects and fungi cause a higher mortality than in stands of normal trees. A general discussion of the mistletoe parasites on trees will be found on page 54. REFERENCE Weir, J. R. Mistletoe injury to conifers in the northwest. U. S. Dept. Agr. Bul. 360: 1-38, pls. 1-4, figs. 1-27. 1916. Precky Woop-Ror Caused by Trametes pini Fries This wood-rot is commonly known as red-rot, ring-shake and peckiness, and is the most destructive wood-rot of fir, spruce, 164 MANUAL OF TREE DISEASES larch and pine in the United States. The symptoms in fir are similar to those in spruce which are described on page 324. The pockets are larger than those found in spruce and the wood is thab @eyoect ce Fia. 23.— Pecky wood- rot; early stage in Doug- Fig. 24.— Pecky wood-rot in las fir. Douglas fir. largely destroyed. In Douglas fir the pockets are at first cir- cular white areas (Fig. 23). Later the pockets increase greatly in number and finally the wood is honeycombed (Fig. 24). Somewhat different symptoms are shown in larch and pine and are described on pages 215 and 291 respectively. The life-history, dissemination of the spores and mode of in- fection of the wood-rotting fungi are treated in a general discus- sion on page 64. FIR DISEASES 165 RepD-BRowNn Sapwoop-Ror Caused by Fomes pinicola Fries The red-brown sapwood-rot is one of the most common dis- eases of spruce, pine, fir, larch and hemlock, wherever these trees grow. ‘The fungus causing this wood-rot occurs less frequently in living trees than it does on dead standing trees and logs. It is thought that the fungus usually attacks living trees which are badly wounded or in generally poor health. Vigorous healthy trees are more rarely affected. The decay progresses very rapidly and the wood is reduced to a light easily pulver- ized mass. The wood of beech, birch, maple and other de- - clduous trees is also destroyed by this fungus. Symptoms. In longitudinal section, the first evidence of the decay shows as whitish spots or streaks irregularly placed. The white spots have reddish brown centers. At this stage the wood is punky and brittle. The spread of the mycelium from these centers soon results in a uniform red-brown, easily pulverized mass of loose fibers. The decayed wood shrinks in all directions, leav- ing numerous cracks which are filled with white mycelial felts. These felts are largely responsible for holding the decayed wood from falling to pieces. The fruiting-bodies of the fungus are formed abundantly and are the most conspicuous of the various shelf-fungi in coniferous forests. When growing from wounds on_ living trees, they are usually hoof-shaped. On logs and dead wood they are broader and thinner. The upper surface is marked by broad rounded concentric folds, each representing the re- sult of a year’s growth. From the center of the top to the margin, the color varies from black to brown and reddish brown. The rounded margin is yellowish in the early summer and later becomes reddish yellow or deep red. The surface of this bright 166 MANUAL OF TREE DISEASES colored. zone appears as if varnished. The under surface is yellowish brown and covered with minute pores. Cause. The red-brown sapwood-rot of conifers is caused by the fungus Fomes pinicola. Infection occurs in wounds which ex- pose the sapwood of the tree. The wood fibers are not de- stroyed completely but are reduced to weak thin-walled struc- tures with numerous cracks and fissures. The life history and control of wood-rotting fungi is more fully discussed on page 64. REFERENCES Schrenk, Hermann von. Polyporus pinicola (Swartz) Fr. In Some diseases of New England conifers. U.S. Dept. Agr. Div. Veg. Phys. and Path. Bul. 25: 24-31, pls. 3-5, fig. 2. 1900. Atkinson, G. F. Polyporus pinicola. Jn Studies of some shade tree and timber destroying fungi. Cornell Univ. Agr. Exp. Sta. Bul. 193 : 222-297, figs. 80-81. 1901. Hedgecock, G. G. Notes on some diseases of trees in our national forests. IV. Phytopathology 4: 181-188. 1914. Srrincy Rep-Brown HEARTWoop-RotT Caused by Echinodontium tinctorium Ellis and Everhart The destructive stringy red-brown heartwood-rot of fir, spruce and western hemlock is a common disease of these trees in western United States. White, Alpine, grand, noble and Douglas fir, Engelmann spruce and western hemlock are known to be affected by this wood-rot. The older stands of firs in the northwestern forests are so badly damaged by this rot that they are practically worthless. Symptoms. The first indication of this heartwood-rot is noticeable in the branch stubs through which the fungus finds entrance to the heartwood. The wood of the branch stubs is a rusty brown FIR DISEASES 167 and from the exterior this rot is identified by the rusty knots. In the heartwood there are three distinct stages in the progress of the decay. As the rot advances, the newly affected wood is discolored and spongy, with occasional light brown spots. This advance rot, as it is called, extends from two to six feet beyond the distinctly red-brown disorganized wood. In more Fie. 25.— Fruiting-body of Echinodoniium tinctorium. advanced stages, the wood turns red-brown and is soggy. The annual rings are separated into sheets which appear as brown cylinders one inside the other. Soon, however, the wood of these partially destroyed rings is dissolved and the tree be- comes hollow. The decay may proceed until only a thin shell of sapwood remains. 168 MANUAL OF TREE DISEASES The sporophores of the causal fungus are formed at the rusty knots and are large hoof-shaped bodies, gray or black above and with numerous large and firm straw-colored or gray spines on the under surface (Fig. 25). The inner substance of the bodies is bright rusty red. The American Indian used the red fungous material for making war paint and thus this fungus has been named the Indian paint-fungus. . Cause. The stringy red-brown heartwood-rot of. western conifers is caused by Hchinodontium tinctorium, a member of the toothed fungi (Hydnaceee). The spores are borne on the outer surface of the teeth on the under side of the fruiting-body. Infection occurs when the spores lodge on the exposed wood of broken branch stubs. For further details concerning the life history and control of the wood-rotting fungi, see page 64. REFERENCE Meinecke, E. P. Forest tree diseases common in California and Ne- vada. U.S. Dept. Agr. Forest Service. Unnumbered publica- tion, pp. 1-67, pls. 1-24. 1914. Brown Pocker HEartwoop-Rot Caused by Fomes roseus Fries The heartwood of fir is frequently destroyed by the brown pocket-rot. This disease occurs also in juniper, larch, spruce, pine and hemlock and occasionally in arbor-vite, beech and maple. Long, cylindrical and pointed pockets of brown char- coal-like decayed wood are formed. The fruiting-bodies of the causal fungus are either thin and shelf-like or thick and hoof- shaped. The under surface of the fruiting-body is rose-colored. This heartwood-rot is more fully described under juniper dis- eases, page 204. FIR DISEASES 169 Brown Heartwoop-Ror Caused by Fomes officinalis Fries (= Fomes laricis (Jacq.) Murrill) Douglas fir is often severely damaged by this heartwood-rot in the Northwest. Larch, pine and other conifers are affected by the same disease throughout western United States. The decayed wood re- sembles the brown checked wood-rot caused by Poly- porus sulphureus (see page 247). In the final stages of decay, the heart- wood is brownish or red-brown. Felts of mycelium form in checks in the brown wood (Fig. 26). The fruiting-bodies of the causal fungus are large hoof- - shaped or globose, with a rough chalky upper surface. The inner substance of the sporophore has a bitter taste. A more complete discussion of this heart- wood-rot will be found under larch diseases, page 216. Fig. 26.— Brown heartwood-rot of Douglas fir. Brown Root- anv Burr-Ror Caused by Fomes annosus Fries This rot of the wood of the roots and lower part of the trunk of fir is occasionally found in the forests of the North- 170 MANUAL OF TREE DISEASES west. Pine, spruce and other conifers are also sometimes affected wherever these trees grow. The wood is discolored and changes from bluish to yellowish and finally becomes red-brown. V/hite pockets with black centers appear in the spring-wood of the rings. Later the pockets coalesce and the brown summer-wood is left in separated sheets. The peren- nial sporophores are shelving or resupinate and are found attached to the diseased roots. The upper surface of the shelving form is light brown and the under yellowish. For further details concerning this root-disease, see under spruce diseases on page 329. Rep-Brown Root- anp Burt-Rot Caused by Polyporus Schweinitzii Fries This root-rot occurs also on pine, larch, spruce, hemlock and arbor-vitee throughout the range of these trees. It is next in importance to the pecky wood-rot of conifers caused by Tra- metes pint. The heartwood of the roots and lower part of the trunk becomes at first yellowish and cheesy and later is red- brown and brittle, resembling charcoal in structure. This wood-rot is more fully discussed under pine diseases, on page 294. YELLOW Root-Rotr Caused by Sparassis radicata Weir This yellow or brownish root-rot of fir, spruce, pine and larch has been recently described as common in northwestern United States.. It seems to be equally as important in that region as the shoe-string and brown root-rots, caused by Armillaria mellea and Fomes annosus. The fungus causing the yellow rot is peculiar in having a long perennial root-like attachment of fungous mycelium which arises from the diseased roots. Other species of the same group of fungi have been suspected of caus=") FIR DISEASES 171 ing root-rots of various conifers and hardwood trees but have never been accurately studied. Symptoms. Lateral roots are attacked even to considerable depths in the soil. The mycelium from the point of infection spreads out in the cambium and bark in yellowish fan-like plates. The root is girdled and killed. The mycelium then penetrates the sapwood, destroying first the medullary-rays. The affected region 1s bordered by a reddish zone and at times by a jet- black line. The heartwood at first is not penetrated because of its highresin-content. Certain areas of heartwood are attacked, however, and long pits formed by the complete destruction of the tissues. At other times the inner layers of heartwood may be largely destroyed, leaving a resinous layer of unaffected wood between the decayed region and the sapwood. The decayed heartwood is brownish or yellowish. Numerous delicate brown strands of mycelium penetrate the wood where openings have been formed. The cambium region is replaced by a thick felt of mycelium. The fruiting-bodies of the causal fungus are formed on the surface of the ground. A long, fleshy, tuber-like body at- tached to the diseased root pushes upward through the soil and bears the upright fruiting-body on its tip. This fruiting-body is a large, fleshy, compact, whitish, much branched structure, often as much as ten inches across and equally as high. The branches terminate as thin leaf-like but much crumpled plates which stand upright or horizontally. The perennial tuber- like attachment to the roots is often fifteen or more inches long and a new fruiting-body is formed from its tip each year. Cause. The yellow root-rot of conifers is caused by the fungus Sparassis radicata of the family Clavariacese. The spores are 72 MANUAL OF TREE DISEASES borne over the surface of the leaf-like plates of the fruiting- body. For further details concerning the life history and con- trol of wood-rotting fungi, see page 64. REFERENCE Weir, J. R. Sparassis radicata, an undescribed fungus on the roots of conifers. Phytopathology 7: 166-177, figs. 1-5. 1917. CHAPTER XIX HACKBERRY DISEASES Two species of hackberry (Celtis) occur in eastern and central United States. These trees are not important forest species and in many sections they are shrub-like. West of the Missis- sippi River, the hackberry is commonly used for shade and ornament. The most important disease of this tree is the witches’-broom. Several leaf-spot fungi and powdery mil- dews are common on hackberry. Although no wood- or root- rots have been recorded as affecting the hackberry, doubtless some of the more common wood diseases of other deciduous trees may also be found in them. The small amount of atten- tion that has been given to the diseases of the hackberry is due to its unimportance as a timber-tree. Powpery MILDEWS Caused by Uncinula parvula Cooke and Peck, and Uncinula polycheta (Berk. and Curt.) ex Ellis Besides the powdery mildew fungus which is associated with the formation of the prominent knots and witches’-brooms, two other species of the same group attack the leaves of the hackberry. The one, Uncinula parvula, is reported through- out the United States, while the other species, Uncinula polycheta, is apparently confined to the southeastern states. The former species causes inconspicuous powdery growths on both sides of the leaf. The black fruiting-bodies are very small and usually confined to the under surface of the leaf, 173 174 MANUAL OF TREE DISEASES while in the latter species dense irregular white patches are formed on the under sides of the leaves, and the black fruiting- bodies are large in comparison with those of the former species. The life histories and methods of control of powdery mildew fungi are discussed on page 37. WITcHEs’-BRooM Caused by a gall-mite and Spherotheca phytoptophila Kellerman and Swingle The hackberry is affected, in central United States, by an important witches’-broom disease. Although mainly impor- tant because of the unsightly appearance of affected orna- mentals, some damage to the tree must result from the loss of energy spent in the development of the brooms. Also due to the death of the branches or their breakage, wounds are formed which allow wood-rot fungi to enter. The lower branches are most commonly affected, although at times brooms are found throughout the crown. Hundreds of brooms are sometimes found on a single tree, causing serious deformation. Symptoms. Two general types of brooms are formed. The open type consists of irregular swellings or knots at the base of a branch from which many short stubby twigs arise. The leader remains healthy, however, and grows to its normal length and other knots with diseased laterals are formed on it at intervals. A closed type of broom results when the leader is diseased and fails to develop normally. For several years, after the first knot with its diseased laterals is formed, the new laterals from the base of those of the previous year cause a compact broom of many deformed and dwarfed branches all arising from a large irregular mass of gall-tissue. Smaller galls may be de- veloped also further out on the diseased laterals. HACKBERRY DISEASES 175 The first indication of the diseased condition can be detected by examining the buds in the winter. Diseased buds are found on wood one year or more old. They are larger in diame- ter than healthy buds of the same length, grayish in color and more open and hairy. When closely examined, it is seen that the scales and inner bud-parts are distorted and enlarged, causing the scales to stand open, exposing the inner parts. Inside of the scales small mites are found. The mycelium of the mildew fungus covers the outsides of the scales and the small black fruiting-bodies of the mildew may be found within the bud on the inner scales and young leaves. The buds of the diseased laterals are more numerous than is normal and they are usually all diseased. Many diseased buds are formed at the bases of these laterals from which develop a new knot with stubby dwarfed branches. The mycelium of the powdery mildew fungus covers the buds and twigs early in the spring and even at times is found on the under sides of the leaves of diseased branches. This causes a whitish powdery appear- ance of these parts. Cause. Two causal agents are always associated with the diseased buds which develop the knots and broom-like growths. One is a gall-mite, a species of Phytoptus, and the other a powdery mildew fungus, Spherotheca phytoptophila. It has never been definitely determined which of these two agents is the more responsible in producing the abnormal growths. The gall-mites are known to cause galls and warts of leaves and twigs and in some instances other powdery mildews have been found growing on the diseased areas produced by these insects. Since, however, the mildew fungus is found growing over and within the diseased buds and the fruiting-bodies are already fully formed within the unopened buds, it seems reasonable to believe that the fungus is present from the very initiation of 176 MANUAL OF TREE DISEASES the diseased condition and may be jointly responsible for the deformation. ‘Two such intimately associated agents, one an insect and the other a fungus, are unusual and deserve more careful study than has been given them. Practically nothing is known concerning the life history of these two parasites and their interrelations, more than has been discussed under symp- toms. Both conidia and perithecia are formed by the mil- dew fungus. The structure, life history and control of the powdery mildew fungi are more fully discussed on page 34. In the case of this disease, control measures seemingly would be confined to cutting out the diseased twigs and brooms. Spraying or dusting could not be expected to yield satisfactory results. REFERENCES Kellerman, W. A., and Swingle, W. T. Branch knot of the hackberry. In Report of the Botanical Department. Kansas Agr. Exp. Sta. Ann. Rept. 1: 302-315, pls. 4-6. 1889. Halsted, B. D. Notes upon Spherotheca phytoptophila Kell. and Swingle. Jour. Mycology 5: 85-86. 1889. Salmon, E. 8S. Sphewrotheeca phytoptophila Kellerm. and Swingle. In A monograph of the Erysiphacee. Mem. Torrey Bot. Club. 9: 76-79. 1900. CHAPTER XX HEMLOCK DISEASES Four species of hemlock or Tsuga occur in the forests of the United States. The two eastern hemlocks are important trees, especially in the northeastern states. The western species are confined to the northwestern states and are large trees. All four species are frequently used as ornamentals. Although several fungous diseases are occasionally found on hemlock, it is less severely affected in general than pine, spruce and fir. In the Northwest, the young trees are killed by a root-rot and the older ones are often affected by the stringy red-brown heartwood-rot. In the East, the leaf-blight, rusts and wood-rots cause but little damage. SEEDLING Root-Ror Caused by Rhizina undulata Fries The roots of three- to five-year-old seedlings of species of hemlock, pine, larch and fir are frequently attacked in the forests of the Northwest by Rhizina undulata. The fungus has been found in several eastern states attached to roots of conifers but its connection with any root disease is not definitely established. The same disease is common in Europe on seed- lings of various conifers and has been known for many years. Symptoms. The fruiting-bodies of the fungus are formed annually and grow on the surface of the ground. They are variable in size, measuring often two or three inches across, irregular in shape, N 177 178 MANUAL OF TREE DISEASES with an undulating, rich brown upper surface bordered at the margin by a narrow white zone (Fig. 27). In wet weather the upper surface becomes mucilaginous. The under surface is more or less fused with the soil. Long white strands of my- celium, arising from the under surface, can be traced to diseased roots. Affected seedlings growing in nursery-beds or in the forest are killed in isolated groups. On pulling the trees, the roots are found to be closely matted with white mycelium. This characteristic, together with the soil being held together by the matted mycelium and the roots being more or less resinous, make this root disease practically indistinguishable Fig. 27.— Fruiting-bodies of Rhizina undulata. from the common shoe-string root-rot caused by Armillaria mellea. This latter fungus is common as a root-rotting fungus of both conifers and deciduous trees and sometimes attacks young seedlings (see page 78). Often, however, the fruiting- bodies of the Rhizina occur plentifully around and envelop we stems of affected seedlings. Cause. The pathogene causing this seedling root-rot is an ascomy- cetous fungus which forms spores in closely packed asci. These stand upright and form the brown upper surface of the fruiting- body. The spores are forcibly shot upward into the air and are blown away. Falling on the ground, they germinate and the abundant white mycelium that is formed penetrates the root- tissues and causes the seedling to die. HEMLOCK DISEASES 179 Control. No specific measures of control have been tried, so far as known. The control measures given on page 81 for the shoe- string root-rot may be applied to this disease as well. REFERENCES Weir, J. R. Observations on Rhizina inflata. Jour. Agr. Res. 4: 93-95, pl. 8. 1915. Hartig, R. Rhizina undulata Fr. the root fungus. Jn Text-book of the diseases of trees, pp. 123-129, figs. 61-70. 1894. LeAF-BLIGHT Caused by Keithia tsuge (Farlow) Durand The leaves of the eastern hemlock are at times killed by this leaf-blight. Instances are reported in which several trees were almost defoliated. This disease is definitely reported only from New Hampshire, Massachusetts and Wisconsin. It may, however, be found at other places in the range of the hemlock. The leaves that are affected turn brown and fall from the twigs. These symptoms occur in the late summer. The fruiting-bodies of the pathogene form during the summer on the affected leaves. They appear as small black pustules bursting through the leaf-epidermis. Ascospores are forcibly ejected from these fruiting-bodies during moist weather. Additional facts concerning the life history of this fungus will be found on page 90, where a similar disease of western arbor-vit is discussed. REFERENCES Durand, E.J. The genus Keithia. Mycologia 6: 6-11, pl. 81. 1913. Farlow, W.G. Notes on the cryptogamic flora of the White mountains. Appalachia 3 : 245-246. 1883. Spaulding, P. Diseases of the eastern hemlock. Proce. Soe. Amer. Foresters 9: 245-256. 1914. 180 MANUAL OF TREE DISEASES Brown-Mo.up L&AF-BLIGHT Caused by Rosellinia sp. ? The importance and prevalence of this disease of hemlock is so far not known. It has been found in North Carolina. The needles of the lower branches become yellow. The af- fected twigs show a growth of yellowish-brown or grayish mycelium covering the bark and investing the bases of the yellow needles. The dead needles either fall off or are held by the tangle of mycelium. Small dome-shaped fruiting- bodies of the fungus are found slightly sunken in the mycelium. Although not definitely determined, this fungus apparently belongs to the genus Rosellinia. It has not yet been definitely established that the brown mycelium is directly responsible for the diseased condition. REFERENCE Graves, A. H. Notes on the diseases of trees in the southern Appa- lachians III. Phytopathology 4: 63-72, pl. 5, fig. 1-10. 1914. LEAF AND CoNneE BLIstTER-Rvusts Caused by Pucciniastrum minimum (Sehw.) Arthur, and P. myrtilli (Schum.) Arthur Two species of the blister-rust fungi attack the green parts of the eastern and Carolina hemlock. These rusts are very similar in appearance and have been found in widely separated localities throughout the range of the two eastern hemlocks. The leaves and cones may be at times so heavily infected that the leaves fall and the cones fail to mature viable seeds. This happens only in the case of individual trees which stand close to the alternate host plants which these fungi require for the completion of their life history. F HEMLOCK DISEASES 181 Symptoms. Although these two species of fungi differ sufficiently so they can be recognized by their microscopical characters, the general appearance of fruiting-structures and the effect on the tree is very similar. The leaves of young trees or of the lower limbs of older trees are much oftener affected than the tops of older trees. Sometimes one-half of the cones may be affected. The most conspicuous symptom of these diseases is the production, on the leaves or cones of golden- yellow or reddish colored blisters in June and July. These blisters burst through the epidermis of the affected parts and when abundant their color stands out prominently against the dark green of the healthy foliage. The spores borne in the blisters sift out as a fine powder and are blown away by the wind. Cause. Two species of the rust-fungi are known to cause the blister- rust of the leaves and cones of hemlock. The life history of these species varies slightly in that different kinds of shrubs are required for their further development. The first species mentioned, Pucciniastrum minimum, occurs on the leaves and cones. This fungus was known on the hemlock previously as Peridermiwm Peckii Thiimen. The spores from the blisters on the leaves cause the in- fection of the leaves of species of Rhododendron. On this host plant, very small yellowish spots are developed on the under sides of the leaves. The spores produced in early spring on the rhododendron leaves infect the newly developed leaves and cones of the hemlock. The second species, Pucciniastrum myrtilli, is known to occur only on the leaves. This fungus was also previously known as Peridermium Peckii. The blisters on the hemlock leaves are more reddish than those of the other species. The 182 MANUAL OF TREE DISEASES spores from the blisters infect the leaves of species of blue- berry. On this host plant are formed small yellowish spots on the under sides of the leaves. Later light brown spots appear in the same areas. The spores produced the following spring from the brown spots cause the infection of the young hemlock leaves. Control. By keeping rhododendrons and blueberry bushes away from hemlock trees, these blister-rusts can be prevented. The heaviest infection of the hemlock occurs when one of these alternate host plants stands within a few feet. REFERENCE Spaulding, P. Diseases of the eastern hemlock. Proce. Soe. Amer. For- esters 9: 245-256. 1914. (Bibliography given.) Lear-, Cone- AND Twic-Rusts Caused by Melampsora abietis-canadensis (Farl.) Ludwig, and Neciwm Farlowit Arthur In addition to the two blister-rusts of hemlock (page 180) two other rust-diseases occur on these trees. In Nova Scotia instances have been noted in which the leaves and twigs of the entire top of the tree were killed by the later fungus. Symptoms. The first species, M. abietis-canadensis, causes a rust on the leaves, cones and twigs similar in appearance to the blister- rusts. This fungus was known on the hemlock previously as Caoma abietis-canadensis on the leaves and as Peri- dermium fructigenum on the cones. The spores from the pustules produced in early summer on the affected parts of the hemlock cause the infection of the leaves of the large- tooth aspen. On this second host small orange or brown- HEMLOCK DISEASES 183 ish spots are produced on the leaves. Later reddish brown pustules are formed (see page 298). Spores formed on the dead aspen leaves the following spring, when blown to the hemlock, cause the infection of the young green parts. The leaves and twigs affected by the second species, Necium Farlowii, may die in midsummer, the leaves falling off. When defoliation does not take place, the infected leaves and twigs bear reddish, swollen, velvety pustules in early spring. The cones may show the same reddish bodies. Cause. These rust-fungi are close relatives of the hemlock blister- rusts. The first species produces eciospores in open pustules which do not have a bladdery covering, as in the blister-rusts. The second species does not produce sciospores but forms teliospores as its only spore-stage. These over-winter and burst the epidermis, producing reddish waxy pustules in the spring. The basidiospores produced by the germination of the teliospores reinfect the young green parts of the hemlock. Thus this rust-fungus requires no alternate host and occurs only on the hemlock. Control. The rust having its alternate stage on poplar leaves may be controlled by keeping poplars separated from hemlocks by a few hundred feet. In the case of the second fungus, which occurs only on hemlock, the affected twigs should be pruned off in the winter and burned, thus destroying the spores of the fungus and preventing further infection. REFERENCE Ludwig, C.A. Notes on some North American rusts with Czoma-like sori. Phytopathology 5: 273-281. 1915. 184 MANUAL OF TREE DISEASES ReEpb-Brown Sapwoop-Ror Caused by Fomes pinicola Fries Hemlock is sometimes affected by this sapwood-rot. It occurs also in spruce, pine, fir and larch. Coniferous wood of all kinds is destroyed by the fungus causing this rot, and the sporophores are very abundant on fallen logs and dead stand- ing trees. The wood is reduced to a red-brown powdery mass held together by numerous plates of mycelium. The sporo- phores have a red varnished margin and a cream-colored under surface. Further details concerning this wood-rot will be found under fir diseases, page 165. Strincy Rep-Brown HEArRtTWoop-Rot Caused by Echinodontium tinctorium Ellis and Everhart The western hemlock is destructively affected by this heart- wood-rot. Firs and spruce are also commonly decayed by the same fungus. In the first stage of decay, the wood is discolored and spongy. The wood then becomes red-brown and the spring-wood of the annual ring is dissolved, leaving the summer- wood in separated cylinders one inside of the other. Later these sheets of summer-wood are destroyed and the tree be- comes hollow. For further details concerning this heartwood- rot, see under fir diseases, page 166. Brown Pocket HEARTWOOD-RoT Caused by Fomes roseus Fries The eastern and western hemlock are sometimes affected by this heartwood-rot, which is also found in juniper, fir, larch, spruce, pine and occasionally in arbor-vite. It occurs prac- tically throughout the entire country wherever conifers are important forest-trees. Long, cylindrical and pointed pockets HEMLOCK DISEASES 185 of brown charcoal-like rotted wood are formed in the heart- wood. The fruiting-bodies of the causal fungus vary from small thin shelves to larger hoof-shaped bodies. The upper surface is black in the older fruiting-bodies, while the new layer of tubes on the under surface. is rose-colored. For further details concerning this heartwood-rot, see under juniper diseases, page 204. The fungus continues to grow in fallen trees and the fruiting-bodies are more commonly found on dead wood than on living individuals. The sapwood is also decayed in dead trees and logs. CusoiwAL Woop-Rot Caused by Polyporus borealis Fries This heartwood-rot does not seem to occur abundantly, since but little mention of it is found in literature. It is re- ported in New York but no definite statements on its importance and range are available. Red spruce is also known to be affected by this wood-rot. Symptoms. In the early stages of the decay, long parallel strands or cords of white mycelium, lying close together, push their way through the wood in the radial and tangential directions. The white strands then disappear, leaving channels in the wood. Because of these perforations and the shrinkage of the wood, it breaks into minute cubes. On the border of the affected wood, the mycelium reaches out into the normal wood in very fine strands. These then develop into the thicker white cords described above (Fig. 28). The fruiting-bodies are formed on the trunk or at the base of the tree. Usually several shelf-like bodies one above the other occur together, forming a cluster. The upper surfaces of the shelves are white and shaggy. The under surfaces are 186 MANUAL OF TREE DISEASES covered with small roundish or sinuous openings. The entire fruiting-body is white or yellowish and soft and spongy. Cause. The cuboidal wood-rot of hemlock and spruce is caused by the fungus, Polyporus borealis. The spores from the tubes opening on the under side of the fruiting-body are blown about by the wind. Infection takes place at wounds. The heart- Fig. 28.— Cuboidal wood-rot of hemlock. wood may be affected from the top to the base of the tree. The sapwood is decayed and the smaller limbs killed at the top of the tree. For further details concerning the life history and control of wood-rotting fungi, see page 64. REFERENCES Atkinson, G. F. Polyporus borealis. In Studies of some shade tree and timber destroying fungi. Cornell Univ. Agr. Exp. Sta. Bul. 193 : 202-208, figs. 56-63. 1901. Hartig, R. Polyporus borealis Fr. In Die Zersetzungserscheinungen des Holzes ete., pp. 54-58, pl. 10. 1878. HEMLOCK DISEASES 187 Rep-Brown Root- anp Butt-Ror Caused by Polyporus Schweinitzii Fries In addition to hemlock, this root- and butt-rot occurs in fir, pine, larch, spruce and arbor-vite. It is a destructive root-disease of these trees throughout their range. The affected wood is first yellowish and cheesy, later changing to a red- brown, uniform rot. The completely decayed wood is brittle, and is similar in appearance to charcoal. For a more complete description of this disease, see page 294. CHAPTER XXI HICKORY DISEASES SEVERAL species of hickory (Carya or Hicoria) occur as com- mon trees in eastern United States. Several fungi cause leaf- spots of hickory (page 30). Besides these, the leaf-mildew, witches’-broom and common white wood-rot are the only dis- eases of importance of these trees. Although these diseases — and probably others are common on hickory practically no mention of them is made in literature. Lear-MILpEw AND WitcHES’-BROOoM Caused by Microstroma juglandis (Bereng.) Sace. The leaves of hickory and walnut in eastern United States are often affected by this disease. Early in the summer the leaflets show a white powdery mildew on the under side. The invaded area of the leaflet is yellowish and defoliation may result. Re- cently the formation of witches’-brooms on shag-bark hickory has been shown to be another symptom of this disease. Brooms are sometimes numerous on the trees and are as much as a yard across. The leaves which appear on the brooms in the spring are yellowish green above and covered with the white powdery growth of the fungus below. The leaflets are smaller than nor- mal and curled. They fall prematurely and leave the brooms bare in midsummer. The fungus causing this disease is sup- posed to be a simple basidiomycete forming numerous short stalks bearing spores on the under sides of the leaf. 188 HICKORY DISEASES 189 REFERENCE ON LEAF-MILDEW AND WITCHES’-BROOM Stewart, F. C. Witches-brooms on hickory trees. Phytopathology 7: 185-187, fig. 1. 1917. Common WuitE Woop-Ror Caused by Fomes igniarius Fries The heartwood of hickory is sometimes reduced to a white soft punk by the false-tinder fungus. This rot is more common and destructive to beech, poplar, oak and maple. The sporo- phores and appearance of the white rotted wood are described under poplar diseases, page 305. CHAPTER XXII JUNIPER DISEASES SEVERAL species of juniper (Juniperus) occur as important forest-trees over the entire United States. These trees and the horticultural varieties of the native and exotic species are the most common conifers used for ornament. In the genus Juniperus are included the low junipers. The juniper is subject to several important wood-rots and rust-diseases. Several destructive heartwood-rots of juni- per are especially common in the Southwest. The rust- diseases of juniper are important both from the economic and ornamental standpoint. Many of the rust-fungi be- longing to the genus Gymnosporangium grow parasiti- cally in the leaves, branches or trunk of juniper. Several types of over-growth occur in the affected tissues. These diseases are interesting because of the complicated life history of the different species requiring various other plants as alter- nate hosts. As certain of these fungi cause the rust-diseases of apple, pear and quince, their control is an orchard as well as an ornamental tree problem. SEEDLING Twi1G-BLIGHT Caused by Phoma sp. Junipers grown in nursery-beds are subject to a twig-blight which has been destructive in certain seasons in Kansas, Ne- braska, Iowa, Illinois and Pennsylvania and may be expected in other localities. By artificial inoculation with the causal 190 JUNIPER DISEASES 191 fungus, the same disease has been found to affect several species of juniper, arbor-vite and cedar. Wet seasons are conducive to epiphytotics of this disease, but it seems never to affect trees more than three or four years old. Symptoms. This twig-blight may appear at any time and continue to spread throughout the growing season on nursery stock less than four years old. When severe, entire beds of stock may be destroyed. The general appearance of the trees is not unlike that produced by sun-scorch, except that the trees of a given bed are not affected uniformly but die in spots, which are ir- regular in outline and gradually increase in size. The small lateral branches are affected first and soon are killed. The mycelium then extends its growth into the main stem and spreads more rapidly upward than downward. Other lateral twigs may thus become affected and killed before the main stem is girdled. Recently killed laterals show bleached lesions of a purplish or grayish cast at the base where they branch from the main stem. When the main stem is affected and it is cut length- wise witha knife, the cambium and wood are seen to be discolored. Girdling is sometimes not accomplished and the long sunken cankers heal over, leaving a flattened stem. ‘The terminal is often killed directly by the mycelium spreading upward into it before girdling has taken place. Minute black fruiting-bodies break through the epidermis of the leaves and bark even before any outward discoloration is apparent. In moist weather, prominent hair-like twisted tendrils composed of hundreds of the spores of the fungus are pushed out from these fruiting- bodies. Cause. The twig-blight of seedling junipers and other conifers is caused by a fungus of the genus Phoma. Only the one type of 192 MANUAL OF TREE DISEASES fruiting-stage, as described under symptoms, is known. Spores are produced in abundance from the fruiting-bodies (pyenidia) during wet weather and may be washed or spattered by rain to neighboring trees. The first infections take place in the lateral twigs, which are quickly killed. The mycelium then spreads into the main stem and proceeds upward, killing the outer wood- tissues and cambium on one side of the tree and running out into other laterals. Control. Experiments so far tried in spraying with lime-sulfur and bor- deaux mixture for the control of this disease have not been suc- cessful. The period of infection extending throughout the grow- ing-season and the nature of the scale-like leaves and the twigs preclude much hope of good results from spraying. Careful eradication of all diseased and neighboring trees may, to some extent, reduce losses by stopping the enlargement of the spots in the beds. REFERENCE Hahn, G. G., Hartley, Carl, and Pierce, R. G. A nursery blight of eedars. Jour. Agr. Res. 10: 533-539, pls. 60-61. 1917. LEAF- AND STEM-Rusts (GENERAL) Caused by species of Gymnosporangium Several species of the rust-fungi belonging to the genus Gym- nosporangium cause more or less important diseases of juniper and cedar. These fungi are strictly parasitic and never grow except in the living tissue of some plant. They are, therefore, confined to the range of the species of juniper and cedar, which are found in the north temperate zone in North America, Europe, Asia and northern Africa. Another important pe- culiarity of these fungi which further restricts the range of each species is that they each require certain kinds of broad-leaf trees JUNIPER DISEASES 193 and shrubs as alternate hosts. Unless the necessary alternate host is present in close proximity to the juniper or cedar, the rust cannot exist, since the life history of the fungus cannot be completed. Trees and shrubs of the order Rosales, family Pomacee, are the most common alternate hosts of these fungi. The life history of all the Gymnosporangium rusts is similar and is described here to avoid repetition below. As stated, these fungi are parasitic throughout their life. They live for a time on a certain species of juniper or cedar and produce spores (basidiospores) which can only cause infection of the leaf, twig or fruit of a certain few or perhaps only a single species of the wild or cultivated apple-like trees, such as apple, pear, quince, haw, mountain ash and service-berry. Here the fungus lives only for a short time and produces spores (seciospores) which do not reinfect other trees of the same kind but can only infect the required juniper or cedar. Thus it is seen that the spores produced on each of the two kinds of hosts are innocuous to the same host and must find lodgment on trees of the other type in order to continue the life history. These rust-fungi over-winter as mycelium in the juniper or cedar leaves or stems. The next season after infection occurs, most of these fungi cause some type of over-growth of the tissues. Such abnormalities are brought about as long swellings or glo- bose galls on the stems, witches’-brooms and leaves transformed into brown globose growths known as cedar-apples. A few of the species cause no abnormal growth and are evident only by the fruiting-structures. The fungi form spores (teliospores) in the early spring on masses of mycelium pushed out from the bark of the twig or epidermis of the leaf. These spore-masses may be in the form of cushions or ridges in the crevices of affected bark or, in the case of the cedar-apples, they consist of long horn-like projections, sometimes an inch or more in length. They appear at first dark brown, due to the color of the telio- spores on the surface. In wet weather the spore-masses become Co) 194 MANUAL OF TREE DISEASES jelly-like and the individual spores germinate, each producing several secondary spores (basidiospores) which are shot off into the air. These spores are carried away by the wind and may find lodgment on the leaves, twigs or fruit of the proper alternate host. Under favorable conditions of moisture, the basidiospores germinate and the tissue of the pomaceous host is penetrated and a new growth of mycelium started. The area of tissue invaded is limited to a small spot which becomes somewhat swollen and light yellow in color (Fig. 29). A short time after these symptoms become apparent, long whitish tubes of fungous tissue are pushed out all over the affected areas (Fig. 30). These tubes some- times split and form a fringe around cup-like depressions in the leaf, twig or fruit, in which are formed powdery masses of yellow spores (sciospores). These dust out, are borne by the wind and may continue the life history of the fungus if they lodge on the leaves or twigs of the proper species of juniper or cedar. These rust-fungi are important because they deform the tree when galls, witches’-brooms or cedar-apples are formed in abun- dance. The tissues of the affected branches die eventually and leave dead areas where wood-rot fungi may enter. On the apple-like hosts, which include not only many important cul- Fic. 29.— Cedar-apple fungus on wild apple leaves. JUNIPER DISEASES 195 tivated fruits but also many valued ornamentals, much damage is caused by defoliation when infection is heavy. Control. The control of these fungi is simple if one or the other of the alternate hosts is eliminated. Although cases have been noted in which a sepa- ration of one to several miles did not totally pre- vent the exchange of spores, a dis- tance of one mile between the two required kinds of trees reduces the amount of infec- tion to a mini- mum. Spraying either the conifer or pomaceous host has not been successful. In some states where junipers are a menace to or- chards because of the rusts, laws are in force requiring the destruction of all specimens within one mile of orchards. Fic. 30.— Cedar-apple fungus on haw leaf. REFERENCE Kern, Frank Dunn. A biologic and taxonomic study of the genus Gymnosporanguim. Bul. N. Y. Bot. Gard. 7: 391-483, pls. 151- 161, figs. 1-36. 1911, 196 MANUAL OF TREE DISEASES LEAF- AND Twic-Rusts Caused by species of Gymnosporangium A few species of the rust-fungi belonging to the genus Gym- nosporangium attack the green twigs and leaves of various jJuni- pers without causing any over-growth of the affected parts. The symptoms of these diseases are confined to the brown spore- masses developed either on the leaf or between the leaves. The life history of these forms is similar to the other species of the same genus and is discussed on page 192. Below are given the hosts and characteristics, in brief, of these diseases. In Colorado, Utah and New Mexico, the Utah juniper is at- tacked by G. inconspicuum Kern. A yellowing of the leaves on the affected twigs may be noticed and in early spring small brown cushion-like spore-masses, the size of a pin-head, are formed from between and around the margins of the appressed scale-like leaves. The alternate stage occurs on species of service-berry. In Colorado a similar appearing species, G. multiporum Kern, attacks the Utah and one-seed juniper. The alternate hosts are not known. In Texas several species of juniper are attacked by G. exiguum Kern. Short brown conical spore-masses, a sixteenth of an inch long, are pushed out from the affected leaves. The alternate host is Crategus Tracyt. In northeastern and north central United States, Juniperus sibirica is attacked by G. Davisii Kern. Spore-masses appear as small brown pustules on the leaves or at the base of leaves on the twig. The alternate stage occurs on species of mountain ash. A foreign species, G. koreaense (P. Henn.) Jackson, recently has been found established in Oregon on an imported juniper, Juniperus chinensis. Spore-masses form on the leaves of the juniper. The alternate stage occurs on cultivated quince and introduced Asiatic species of quince and pear. JUNIPER DISEASES 197 CEDAR-APPLES Caused by Gymnosporangium juniperi-virginiane Schw. and G. globosum Farlow The two diseases of the red juniper known as cedar-apples or cedar-flowers are similar in nature and are found commonly in eastern and central United States. The first pathogene mentioned above has its alternate stage on the culti- vated apple and other species of Malus, while the latter pathogene occurs on various species of haw, mountain ash and the cultivated Fig. 31.— Cedar-apples, early apple, and pear. The junipers EBSD Oa oute Shes a0: are often covered with hundreds of the brown, globose galls Fic. 32.— Cedar-apple in late autumn, one year after infection. which spoil the appearance of ornamental trees and result in more or less damage to the twigs and general vigor of the tree. The two pathogenes are the cause of ap- ple and pear rust respectively and cause serious losses in yield when they cause defoliation. Climatic conditions and the proximity and abundance of the two kinds of hosts In the same locality are the deter- mining factors which influence the severity of these diseases on both hosts. Symptoms. Brown-colored bodies called cedar-apples or cedar-flowers are 198 MANUAL OF TREE DISEASES produced on the small twigs of the red juniper. When very young, the galls can be seen to start as outgrowths of the juniper leaves (Fig. 31). The tissues of the leaf are stimulated to over- growth and finally form, in a single season, the large cedar- apples, which are often an inch in diameter (Fig. 32). In this Fig. 33.— Cedar-apple in spring of second year, showing expanded spore-horns. condition they pass the winter, and the following spring brown horns of spores are pushed out from the surface of the cedar- apples (Fig. 33). In the former species these horns are about one inch long and cylindrical, while in the latter fungus they — are about one-half inch long and are flattened or wedge-shaped. JUNIPER DISEASES 199 Cause. Cedar-apples on juniper are caused by two different species of the rust-fungi, Gymnosporangium juniperi-virginiane and G. globosum. ‘The life history of these fungi is described on page 192 in the general discussion of several species of the same genus. In the case of the two cedar-apple rusts, the leaves of the juniper are infected by eciospores formed on the apple, pear, haw or other pomaceous host. This takes place during midsummer or in the fall and no symptoms on the juniper are apparent until late spring of the next season. At that time the infected leaf shows a small greenish outgrowth, and in the summer from this small beginning the large cedar-apple develops (Fig. 32). The tissue inside the gall is made up of a mixture of large host-cells and intercellular mycelium. The outer layers of the gall are eorky and reddish or chocolate-brown. Scattered over the sur- face, in late autumn, are numerous depressions from each of which a bundle of hyphe grow out the following spring and form the horns covered with teliospores. REFERENCES Hesler, L. R., and Whetzel, H. H. Manual of fruit diseases, pp. 63- 71, 341-344, figs. 17-19, 94. 1917. Weimer, J. L. Three cedar rust fungi, their life histories and the diseases they produce. Cornell Univ. Agr. Exp. Sta. Bul. 390: 507-549, figs. 136-157. 1917. Heald, F. D. The life history of the cedar rust fungus Gymno- sporangium Juniperi-virginiane Schw. Nebraska Agr. Exp. Sta. Ann. Rept. 22: 105-113, pls. 1-18. 1909. Reed, H.S., and Crabill,C. H. The cedar rust disease of apples caused by Gymnosporangium Juniperi-virginiane Schw. Virginia Agr. Exp. Sta. Tech. Bul. 9: 3-106, figs. 1-23. 1915. Giddings, N. J., and Berg, A. Apple rust. West Virginia Agr. Exp. Stas Bull 154275—73, piss 1-10) £95: Coons, G. H. Some investigations of the cedar rust fungus. Nebraska Agr. Exp. Sta. Ann. Rept. 25: 217-246. 1912. Pammel, L. H. The cedar apple fungi and apple rust in lowa. Iowa Agr. Exp. Sta. Bul. 84: 1-386, figs. 1-11. 1905. 200 MANUAL OF TREE DISEASES Rust WircHes’-Brooms Caused by Gymnosporangium Nidus-avis Thaxter, G. jwvenescens Kern and G. Kernianum Bethel Three witches’-broom diseases are caused by species of rust-fungi on different junipers. The first species mentioned above causes witches’-brooms of the red juniper in eastern and central United States. The brooms are simply tufts of many branches which are formed from the part of the parent branch affected by the rust-fungus. The leaves of the brooms are usu- ally of the pointed, awl-shaped, juvenile type. The second species causes large brooms on the red and Rocky Mountain juniper in the Rocky Mountains and in northwestern and north central United States. The leaves of these brooms also are of the juvenile type. The third species causes globose, compact brooms on the Utah juniper in western Colorado. The leaves on the brooms on this tree are scale-like. The life history of all three species is similar to the other rusts of this type occurring on junipers and is discussed on page 192. The spore-masses in the first species appear as linear cushion-like brown masses bursting the bark of the affected branches, while in the other two species they are small hemispherical brown bodies, the size of a pin-head or smaller and arise from between the leaves or in the leaf-axils. Various species of service-berry are the alternate hosts for these three species. The first species is known to infect the quince also. BRANCH-GALLS Caused by several species of Gymnosporangium Abrupt swellings of the stems of the various species of juniper are often caused by species of the rust-fungi belonging to the genus Gymnosporangium. Other species of the same group of rusts cause cedar-apples and long fusiform “branch-swellings, JUNIPER DISEASES 201 and a few produce spore-cushions on the normal green twigs and scale-like leaves. ‘The life history of these fungi is described on page 192. The main characteristics of the forms causing abrupt swellings are given below. The red juniper is affected in southeastern and south central United States by Gymnosporangium trachysorum Kern. Small knots or galls as large as an inch in diameter and an inch and a half long are formed on the small branches. The spore-horns are pushed out from these galls and are wedge-shaped and less than a half inch long. The alternate stage occurs on species of haw. In the same region the red juniper is attacked by Gymnospo- rangium floriforme Thaxter. Small gall-like excrescences as large as one-half inch across and occasionally globose swellings an inch in diameter are formed on the branches. The horns of spores are cylindrical and pointed and vary from an eighth to one-half inch in length. One species of haw (Crategus spathu- lata) is known to be the alternate host for this rust. Along the coast of the Gulf of Mexico from Mississippi to Florida, several species of juniper often show reddish brown globose galls, a quarter to one-half inch in diameter. The fungus causing this gall is Gymnosporangium bermudianum (Farlow) Earle. This species is peculiar and is different from all others of this group in that no alternate host is required for its develop- ment. Both the teliospores and eciospores are formed on the same galls on the juniper. The cluster-cup stage is followed by teliospore masses smaller than a pin-head. In northwestern United States and adjacent Canada, the dwarf juniper and Juniperus sibirica are attacked by Gymnospo- rangium juniperinum (L.) Mart. Hemispherical swellings half an inch to two inches long are formed on the larger branches and more or less globose galls an inch in diameter appear on the smaller branches. The spore-masses are flat and cover large areas of the galls. The alternate hosts are species of mountain ash. 202 MANUAL OF TREE DISEASES In the same region as above, the Rocky Mountain juniper is attacked by Gymnosporangium Bethel: Ikern. Irregular gall- like knots are produced which are two or three times the diameter of the normal branch. Several knots breaking out ad- jacent to each other form galls similar to the black knots com- mon on plum and cherry. Short wedge-shaped spore-horns about an eighth of an inch long are pushed out from the bark of the galls. Several species of haw are known to be the alternate hosts for this rust. In northwestern and southwestern United States, the Rocky » Mountain, Utah and one-seed junipers are attacked by Gym- nosporangium Nelsoni Arthur. Hard woody globose galls as large as two and one-half inches are formed. ‘The spore-masses are flattened and about an eighth of an inch high. ‘The alter- nate hosts of this species are the quince, pear and species of service-berry. The red juniper in northeastern and north central United States is attacked by Gymnosporangium corniculans Kern. Irregularly lobed excrescences as large as an inch in diameter are produced. The spore-horns are conical and about one- eighth of an inch high. The alternate hosts are species of serv- ice-berry. FustrorM BRANCH-SWELLINGS Caused by species of Gymnosporangium In addition to cedar-apples and galls or knots, several species of the rust-fungi cause long spindle-shaped swellings of the branches of species of juniper. The life history of these fungi is discussed on page 192 and only the hosts and outstanding characteristics of the diseases are given below. In eastern, southeastern and central United States, the red and dwarf juniper and J. sibirica are commonly affected by Gymnosporangium germinale (Schw.) Kern. The branches are slightly enlarged, often for several inches in length. The spore- JUNIPER DISEASES 203 masses break through the bark as orange-yellow hemispherical pustules about an eighth of an inch high. The alternate hosts are quince, apple and species of service-berry and haw. In northeastern United States and westward to Wyoming and Colorado, the dwarf juniper, and Juniperus sibirica are affected by Gymnosporangium clavarieforme (Jacq.) DC. The branches of all sizes are attacked and slightly swollen for several inches. Spore-horns are produced in abundance in the spring from the swellings. They are brownish yellow and about one-half inch long. The alternate stage of this rust is produced on quince and species of service-berry. Along the Atlantic Coast the red juniper is attacked by Gym- nosporangium effusum Kern. Long slender enlargements of the smaller branches less than an inch in diameter are pro- duced. This fungus also causes swellings on the trunks. The spore-masses are wedge-shaped and often as large as one- half inch high by a quarter of an inch long at the base. The alternate host for this species is unknown. Several species of juniper in Colorado, New Mexico and Ari- zona are attacked by Gymnosporangium gracilens (Peck) Kern and Bethel. Long spindle-shaped swellings of the branches are formed. The spore-masses break through the bark in long rows and are about an eighth of an inch high. Species of Fendlera and Philadelphus are alternate hosts of this rust. In the region extending from northeastern United States to Colorado and Wyoming, the red juniper and Juniperus sibirica are attacked by Gymnosporangium cornutum (Pers.) Arthur. The smaller woody branches are slightly enlarged. ‘The spore- masses are flat or cushion-like and not extensive. Mountain ash is the alternate host. In a restricted region in Kentucky and Missouri, the red juniper is attacked by Gymnosporangium exteruwm Arthur and Kern. Short spindle-shaped swellings are produced and the spore- masses in the spring are flat and anastomosing. ‘The alternate 204 MANUAL OF TREE DISEASES host for this species is Porteranthus (Gillenia) stipulatus (Muhl.) Britton. Waitt Bark Caused by Cyanospora albicedre Heald and Wolf This disease is common on the mountain juniper throughout its range in Texas. White patches, either small or extensive, occur on the bark of the young twigs and larger branches of young trees. The twigs are killed after the white areas have encircled them. Many of the branches, or the entire tree, may be killed in this manner. Shading seems to make the twigs and branches more susceptible. Upon the whitened areas of the bark numerous: grayish pustules are formed, containing the fruiting-bodies of the fungus. After the bark is decayed, the pustules stand out prominently. Projecting from the upper surface of the grayish pustules are one to three short beaks which represent the openings of the fruiting-bodies buried in the pus- tules. Ascospores are formed in these fruiting-bodies and ooze out through the openings during moist weather. REFERENCE Heald, F. D., and Wolf, F. A. The whitening of the mountain cedar, Sabina sabinoides (H. B. K.) Small. Mycologia 2: 205-212, pl. 31, figs. 1-3. 1910. Brown Pocket HEARTWooD-RotT Caused by Fomes roseus Fries This heartwood-rot was first described as a disease of juniper, but recently has been found commonly in fir, larch, spruce, pine, hemlock and occasionally in arbor-vite, birch and maple, over practically the entire United States wherever conifers are im- portant forest-trees. It may be confused in some trees with the red-brown root- and butt-rot caused by Polyporus Schweinitzir (see page 294), unless the fruiting-bodies are present to identify it. JUNIPER DISEASES 205 Symptoms. The wood of the juniper is characteristically affected. Long cylindrical and pointed pockets of brown charcoal-like decayed wood are formed. At first these pockets are more or less sepa- rated and vary from one to several feet in length. Later they may increase in diameter and merge with neighboring pockets, forming large irregu- lar decayed areas. The de- ecayed’ wood in juniper is dark brown but in other trees may be lighter if the normal wood is light colored. | It breaks into cubes and is easily powdered. With a knife blade the charcoal-like cubes may be scraped from the cavity, leaving it smooth. The wood around these cavi- ties is normal and of the natural color. The fruiting-bodies of the causal fungus on juniper are produced in the holes in the trunk where branch stubs are inclosed. They conform to the size and shape of the Fic. 34.— Fruiting-bodies of Fomes hole. When formed on logs, athe they vary from thin shelves to thick hoof-shaped rose- colored bodies which are usually small (Fig. 34). The upper surface may become black with age while the mar- gin and under surface of newly formed pores is pinkish red. The internal structure is flesh-colored or pinkish. 206 MANUAL OF TREE DISEASES The pores in the under surface are minute and the tubes very short. Cause. The brown pocket-rot of conifers is caused by the fungus Fomes roseus (formerly called Polyporus carneus Nees). The fruiting-bodies described above are perennial and are formed from dead areas on living trees or on the dead trees after they fall. Infection seems to take place mostly near the base of the tree and the rot is confined to the lower part of the trunk. The wood is destroyed in the pockets by the extraction of the cellu- lose. The lignin remains and the fibers retain their entirety, although the walls are much thinner than normal. For a fuller description of the life history and control of wood-rotting fungi, see page 64. REFERENCES Schrenk, Hermann von. Red rot, or pecky cedar (Polyporus carneus). In Two diseases of red cedar, caused by Polyporus juniperinus n. sp. and Polyporus carneus Nees. U.S. Dept. Agr. Div. Veg. Phys. and Path. Bul. 21: 16—20, pls. 5-7, fig. 3. 1900. Hedgecock, G. G. Notes on some diseases of trees in our national forests. IV. Phytopathology 4: 181-188. 1914. Wuite Pocket HEartwoop-Rot Caused by Fomes juniperinus Schrenk Junipers are affected by this destructive heartwood-rot in central United States. At times, the trees are made hollow for several feet up and down the trunk. Trees more than twenty-five years old are more often attacked than younger individuals. Symptoms. Varying with the stage to which the decay has progressed, the affected trees show one or more large holes at the center or are JUNIPER DISEASES 207 hollow. At first the decayed areas are a few inches in length and pure white and are separated from one another by several inches of sound wood which appears normal except that it is somewhat brownish. Soon the white areas become holes with their inner surfaces lined with white fibers mixed with a reddish yellow felt of mycelium. The wood around the holes is brown- ish and shades off gradually to the deep red normal wood. The amount of soft white fibers around the edges of the large hole is considerable and very striking in appearance when compared with the normal red wood. When the holes become large, they often fuse and cause hollow trunks. In very large trees there may be several holes parallel to each other. The fruiting-bodies of the causal fungus are very rare and appear at branch wounds. ‘They are woody and usually hoof- shaped. The upper surface is at first yellowish orange and later turns to black with a yellowish margin. When young the top is smooth but with age it becomes fissured. The lower surface is yellowish brown. The inner substance of the fruiting-body is reddish orange. A new layer of tubes is formed each year. Cause. White pocket heartwood-rot or white rot of junipers is caused by Fomes juniperinus. The fruiting-bodies described above are very rarely found. Infection is initiated by spores which lodge on a broken stub of a branch. ‘The mycelium penetrates into the center of the heartwood of the trunk where the first evi- dence of decay is the turning white of the normally red wood. Later new areas of decay originate a few inches above and below. The lignin is abstracted from the cell-walls and the primary layers of the walls are dissolved. These two actions leave the remainder of the walls pure white and unattached to one an- other, so that they fall apart leaving a hole in the wood. ‘The life history and control of the wood-rot fungi are more fully discussed on page 64. 208 MANUAL OF TREE DISEASES REFERENCES ON WHITE Pocket HrArRtTwoop-RoT Schrenk, Hermann von. White rot of the red cedar (Polyporus juni- perinus n. sp.). In Two diseases of red cedar, caused by Poly- porus juniperinus n. sp. and Polyporus carneus Nees. U. S. Dept. Agr. Div. Veg. Phys. and Path. Bul. 21: 9-16, pls. 1-4, figs. 1-2. 1900. Hedgecock, G. G., and Long, W. H. Preliminary notes on three rots of juniper. Mycologia 4: 109-114, pls. 64-65. 1912. YELLOW Woop-Rot Caused by Fomes Earlei (Murrill) Sace. (? = Fomes juniperinus Schrenk) This wood-rot is similar in appearance to the white heartwood- rot of the red juniper. The yellow wood-rot occurs more or less commonly in Arizona, New Mexico, Texas and Colorado in mountain, one-seed and Utah juniper. The rot is most de- structive in New Mexico, and at times the tree is so weakened that it breaks over. Symptoms. Long longitudinal holes several inches in diameter are formed in the heartwood. The holes are partially filled with decayed wood matted together with light brown mycelium. The wood around the holes is yellowish or light brown in color. Both the heartwood and sapwood may be invaded and destroyed, al- though the holes are usually confined to the heartwood. The sporophores of the causal fungus are attached to the affected tree. They emerge from the furrows or depressions in the bark, usually within ten feet of the ground. They are hoof-shaped to cylindrical, woody bodies, brownish to black and deeply checked on top and yellowish beneath. The inner substance of the sporophore is brownish or orange- yellow. The pores on the under surface are rather large and circular. JUNIPER DISEASES 209 Cause. The yellow wood-rot of the species of juniper found in the Southwest is caused by a fungus named Fomes Earlei. There is but little difference between this fungus and Fomes juni- perinus, causing the white pocket heartwood-rot of red juniper in eastern United States. Very few sporophores of Fomes juniperinus have been found, although the rot caused in red juniper is common. Sporophores of Fomes Earle: are common where the trees are affected. It is believed by some that the two species are identical but because very few specimens of Fomes juniperinus are available for comparison, this has not been fully determined. The rots are somewhat different al- though similar in many respects. These differences may be due, however, to the host and do not necessarily indicate that the fungi causing them are different species. Further details concerning the life history and control of wood-rot fungi will be found on page 64. REFERENCE Hedgecock, G. G., and Long, W. H. Preliminary notes on three rots of juniper. - Mycologia 4: 109-114, pls. 64-65. 1912. Strincy Brown Woop-Ror Caused by Fomes texanus (Murrill) Hedgecock and Long This wood-rot affects both the heartwood and sapwood of mountain, Utah and one-seed juniper. The rot is very destruc- tive and common in Texas and New Mexico. Symptoms. The first signs of the decay are evident as small pockets of light brown tissue in the spring-wood of the annual rings. These pockets soon merge and the spring-wood becomes reddish _ brown and is partially or entirely destroyed. This action leaves concentric zones of badly rotted and apparently sound wood P 210 MANUAL OF TREE DISEASES which is characteristic of this wood-rot. Hollow trunks are not formed. The less affected summer-wood of the rings and the wood bordering the decayed area are yellowish brown. The sapwood and bark are affected and permeated by the reddish yellow mycelium. The sporophores of the causal fungus appear from crevices in the bark where the fungus has emerged from the sapwood and inner bark. They are hoof-shaped or cylindrical woody bodies with a light yellowish or brown to black checked upper surface. The yearly growth of the sporophore is apparent in the concen- tric furrows on the upper surface. The under surface is light yellowish and the pores are very small. The inner structure is yellowish. Cause. The stringy brown wood-rot of junipers in the Southwest is caused by the fungus Fomes texanus. No definite studies are reported on the method of infection. The general life history and control of the wood-rot fungi are discussed on page 64. REFERENCE Hedgecock, G. G., and Long, W. H. Preliminary notes on three rots of juniper. Mycologia 4: 109-114, pls. 64-65. 1912. BasaLt Hrartwoop-Rot Caused by Poria Weirii Murrill This heartwood-rot is the most important basal decay of the western red cedar throughout northwestern United States. After the tree falls, the heartwood and sapwood of the entire tree are soon destroyed by the same fungus. In the first stages of decay, the wood is uniformly split into its separate annual rings. The affected wood is brown and brittle. The causal fungus forms fruiting-bodies on the fallen trunks of the affected trees. These fruiting-bodies are brown and JUNIPER DISEASES 2 rather soft sheets of fungous material spread over extensive areas on the sides and bottom of the log. A single fruiting-body may extend for several feet along the log. The surface of the fruiting-body is covered with very fine pores. Two or three layers of tubes may be found representing as many years of successive growth and spore production. REFERENCE Murrill, W. A. An enemy of the western red cedar. Mycologia 6: 93-94, pl. 122. 1914. CHAPTER XXIII LARCH DISEASES Tue three native species of larch or Larix are important forest-trees in northeastern and northwestern United States. The eastern and European larch are frequently used as orna- mentals. The eastern larch is commonly affected by several wood- and root-rots. Of these, the pecky wood-rot and red- brown sapwood-rot are most destructive. The leaf-rusts are rare. In the Northwest, the larch is not only subject to sev- eral wood- and root-rots but is also seriously damaged by a dwarf mistletoe which causes large swellings and witches’- brooms. The seedlings are often killed by a fungus which causes a root-rot. SEEDLING Root-Rot Caused by Rhizina undulata Fries Seedlings of the western larch are killed by this root-rot in northwestern United States. It may be found also in some northeastern states since the fungus is known to occur in this region. The diseased roots of seedlings from three to six years old are matted together by an abundant growth of white my- celium. The fruiting-bodies of the pathogene are formed on the surface of the ground. They are dark brownish, undulat- ing structures with a light colored margin when young. A fuller description of this disease is given under hemlock diseases, page 177. Lear-Rusts Caused by Melampsora Bigelowii Thiim. and M. Meduse Thiim. The needles of larch are sometimes affected by two similar rusts. These diseases have been found in various localities 212 LARCH DISEASES 213 and may be expected throughout the northern states from the Atlantic to the Pacific. The fungi causing these two dis- eases are closely related to the several other rust fungi of pine, spruce, fir and hemlock. Symptoms. The rusts of larch are so similar that they cannot be identified without the use of a microscope. The affected needles in early spring show small whitish pustules bursting through the epidermis. The epidermis of the leaf covering of the pustules breaks open and the spores within are blown away by the wind as a fine dust. The needles then turn yellow and may fall off. Cause. The rust diseases of larch are caused by Melampsora Bigelow and M. Meduse. Besides the stage produced on the larch leaves, each of these fungi requires a period of growth on other kinds of plants. The spores (aciospores) from the pustules caused by the first mentioned species infect the leaves of several kinds of willows. In the latter named _ species the xciospores infect the leaves of certain poplars. On the willows and poplars other spores (urediniospores) are produced which continue the life history of the fungi. Over-wintering teliospores on these two hosts germinate in the spring and pro- duce basidiospores which infect the young leaves of the larch. These facts in the life history of the two rust fungi make it evident that the appearance of the diseases on the larch is de- pendent on the presence of poplars or willows in close proximity. A blister-rust of larch needles which also occurs rarely in this country is caused by Melampsoridium betule (Schum) Arthur. This fungus attacks birch in the United States but the stage on larch does not seem to be common. It is known on both birch and larch in Europe. 214 MANUAL OF TREE DISEASES MISTLETOE Burt AND WItTCHES’-BROOM Caused by Razoumofskya laricis Piper The mistletoe disease of larch is common and destructive in northwestern United States. It is especially abundant in open stands and causes but little damage in the dense forests. In moist and fertile areas, the larch attains full development and is only rarely deformed by the mistletoe. On the other hand in regions of light rainfall, variable temperature, low humidity, dry soil and especially in open stands, the growth of the mistletoe is favored and the tree suppressed. Measure- ments made of unaffected and badly infested trees show that the rate of growth of the larch may be reduced to one-half the normal. Symptoms. Young and old larches are affected. The seeds of the mistle- toe produce infection if they fall on the green twigs. Burls are produced in the trunk and larger branches due to the irri- tation caused by the roots of the mistletoe. Infected younger branches are stimulated to produce abnormal twigs, forming witches’-brooms. The foliage area of the tree is reduced by the deforming of the branches and the general development of the tree is suppressed. Cause. This burl and witches’-broom disease is caused by one of the species of dwarf mistletoe, Razowmofskya laricis. The roots of the parasite penetrate the bark and wood and grow down the branch for some distance, sometimes entering larger branches or the trunk. The irritation caused by the roots of the parasite results in an increased growth of the affected parts. The parasitic plants are inconspicuous, never being more than about four inches tall. A cluster of yellowish LARCH DISEASES 215 leafless stems growing out from the bark is all that can be seen. A general discussion of mistletoe diseases will be found on page 54, REFERENCES Weir, J. R. Larch mistletoe: some economic considerations of its injurious effects. U. S. Dept. Agr. Bul. 317: 1-25, figs. 1-13. 1916. Weir, J.R. Mistletoe injury to conifers in the northwest. U.S. Dept. Agr. Bul. 360: 1-38, pls. 1—4, figs. 1-27. 1916. Precky Woop-Rot Caused by Trametes pini Fries Red-rot, ring-shake, peckiness or pecky wood-rot is the most destructive wood-rot of conifers in the United States. It is common in larch. The characteristics of the rot in larch are similar to those produced in spruce, with the exception that the action in the formation of pockets is less localized. The spring-wood of the affected annual rings is largely destroyed, leaving the denser summer-wood partially decayed and red in color. Black lines are formed at irregular places. The wood of the larch is thus more completely destroyed than that of the other conifers. The sapwood and bark are readily in- vaded and the living tissues killed, thus causing the death of the parts of the tree above, as in the spruce and fir. A more complete description of this wood-rot is given under spruce diseases, page 324. Rep-Brown SApwoop-Ror Caused by Fomes pinicola Fries Larch wherever it grows is commonly affected by this wood- rot. Spruce, pine, fir and hemlock are also affected. The wood is reduced to a red-brown powdery mass held together by numerous plates of whitish mycelium. The sporophores 216 MANUAL OF TREE DISEASES of the causal fungus are formed abundantly on the diseased trees and on fallen logs. They have a red varnished margin and a cream-colored under surface. Fuller details concerning this heartwood-rot will be found under fir diseases, page 165. Brown Heartwoop-Rot Caused by Fomes officinalis Fries (= Fomes laricis (Jaeq.) Murrill) This brown heartwood-rot is common and very destructive in western United States in larch, pine, Douglas fir and other conifers. In California and Nevada, sugar pines are the most destructively attacked. In the Northwest, Douglas fir, western larch, lodge-pole and western yellow pine are often seriously affected. The rot resembles to some extent the brown checked wood-rot caused by Polyporus sulphureus (see page 247). Symptoms. The affected heartwood is brownish or red-brown in color. Felts of the mycelium of the fungus form in cracks in the wood. The sporophores of the causal fungus are not formed abun- dantly on the affected trees. They are large hoof-shaped or globose bodies with a white, roughened, chalky upper surface. The white material will rub off like powdered chalk. The fruiting-bodies when young are soft and watery but become very brittle when old. The inner structure is white, bitter to the taste and has a distinct mealy odor. The under surface is convex, whitish and covered with small pores. Cause. The brown heartwood-rot of conifers in the western forests is caused by Fomes officinalis. This fungus also is known by the name Fomes laricis. Infection takes place when the spores from the tubes on the under side of the fruiting-body lodge in open wounds where heartwood is exposed. For further detail LARCH DISEASES DAW concerning the general life history and control of the wood- rotting fungi, see page 64. REFERENCE Meinecke, E. P. Forest tree diseases common in California and Nevada. U.S. Dept. Agr. Forest Service. Unnumbered pub- lication, pp. 1-67, pls. 1-24. 1914. © Brown Pocket HEARTWOOD-RotT Caused by Fomes roseus Fries This heartwood-rot is common in larch as well as in fir, spruce, pine and hemlock, in almost every section of the country where these trees grow. The rot may be confused at times with the red-brown root- and butt-rot caused by Polyporus Schweinitzir (see page 294). The decayed wood is brown, easily powdered and looks like charcoal. At first long cylindrical or pointed pockets of decayed wood are formed. Later these pockets may join and large areas of the heartwood are uniformly brown rotted. The fruiting-bodies of the causal fungus are produced at branch stubs on affected trees or on the sides of fallen timber. They may be either small and thin structures or large hoof- shaped bodies. The under surface is rose-colored. For further details concerning this heartwood-rot, see under juniper diseases, page 204. Rep-Brown Root- anp Burtt-Rot Caused by Polyporus Schweinitzii Fries Fir, pine, spruce, hemlock and arbor-vite in addition to, the larch are affected by this wood-rot wherever these kinds of trees grow. It 1s next in importance to the pecky wood-rot of these trees. The affected heartwood of the roots and lower part of the trunk is at first yellowish and cheesy but later be- comes red-brown and brittle. This wood-rot is more fully described under pine diseases, page 294. 218 MANUAL OF TREE DISEASES YELLOW Root-Ror Caused by Sparassis radicata Weir In the Northwest the roots of larch are often destroyed by this root-rot. Fir, spruce and pine are affected by the same disease. The bark and sapwood of the roots are killed. Yel- lowish fan-shaped plates of mycelium are found in the bark. The medullary-rays and heartwood are also decayed and be- come yellow or brown. The fruiting-bodies of the causal fungus are peculiar. They are attached to the diseased roots by long, fleshy stalks. New fruiting-bodies are formed each year from the tip of the stalk. They are large, white, compact, fleshy structures covered with curled and lacerated leaf-like plates. These thin plates stand upright on the upper portion of the fruiting-body or horizontally from the sides. The spores of this fungus are borne over the entire exposed surface of the fruiting-body. For further details concerning this root-rot, see under fir diseases, page 170. CHAPTER XXIV LOCUST DISEASES Tue native species of locust are unimportant forest-trees. The common locust of eastern United States (Robinia Pseuda- cacia) was more frequently used as an ornamental in previous years than at present. Insect damage has made the tree difficult to grow. The only fungous diseases of the locust that have considerable importance are the yellow and brown checked wood-rots. The yellow wood-rot is caused by a fungus that grows only in the wood of the locust. This rot is common in ornamental trees and often causes their death. YELLOW Woop-Rot Caused by Fomes rimosus Berkeley The yellow wood-rot of the trunk and branches of the locust is common throughout the range of this tree. Young trees less than six inches in diameter are rarely affected. Symptoms. The central portion of the heartwood is reduced to a soft yellow spongy mass for several feet up and down the trunk or limb. From this central decayed area, as seen in cross-section, several V-shaped bands reach out radially toward the sapwood. When the wood is split lengthwise, these bands of decay are seen to be one or two inches wide. At the center of each band is a small reddish core and extending upward and downward from this core the partially decayed wood varies from orange- 219 220 MANUAL OF TREE DISEASES yellow to light straw-yellow at the edge of the band. When the bands have reached the cambium and bark, compact red- brown felts of mycelium replace the destroyed tissues. In tangential section the narrow bands show as yellow lens-shaped areas with red centers. The radial bands of decay become more numerous and finally coalesce, and in this way all the heartwood and sapwood is decayed. The sporophores of the pathogene appear at various places on the bark where the mycelium has penetrated the sapwood Fig. 35.— Upper surface of fruiting-body of Fomes rimosus. and bark. They are at first small, red-brown, hard knobs. Each year a new layer of pores is added to the under surface. After several years’ growth large brackets or hoof-shaped bodies are formed. The upper surface is dark brown or black and much roughened by numerous fissures which divide the surface into irregular squares (Fig. 35). The under surface is dull red-brown and extends upward over the edge of the sporophore LOCUST DISEASES 221 in a smooth roll. The pores on the under surface are barely visible. Cause. The yellow wood-rot of locust is caused by the fungus Fomes rimosus. It is similar in appearance to Fomes igniarius except when it is broken open the older layers of tubes do not show the white filling. The spores from the tubes on the under surface of the sporophore infect the locust at branch stubs or through the tunnels made by the locust borer. The mycelium, after destroying the central portion of the heartwood, reaches out along the medullary-rays and initiates the bands of decay. The yellow wood-rot fungus is not known to continue growing in dead wood and timber made from affected wood is said to last as long as sound timber. For further details concerning the life history and control of wood-rotting fungi, see page 64. REFERENCES Schrenk, Hermann von. A disease of the black locust (Robinia pseudacacia L.). Missouri Bot. Gard. Ann. Rept. 12: 21-31, pls. 1-3. 1901. Schrenk, Hermann von, and Spaulding, P. Black locust disease eaused by Fomes rimosus. . Jn Diseases of deciduous forest trees. U. S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 45-46. 1909. Brown CuHeckeD Woop-Rot Caused by Polyporus sulphureus Fries The heartwood and sapwood of locust is often reduced to a red powdery mass by the sulfur fungus. Oak, chestnut, walnut, butternut, maple and alder are the other principal kinds of trees commonly affected by the same rot. The sapwood and bark may be invaded and the tops of the trees or large limbs are thus killed. The sulfur-yellow and orange-colored fruiting- bodies of the causal fungus are produced in late summer from wounds or from the bark where the mycelium has invaded the 222 MANUAL OF TREE DISEASES sapwood. The reddish colored decayed wood splits into small cubes with plate-like sheets of mycelium filling up the cracks between. This wood-rot is similar in its effect on the different kinds of trees and is more fully described under oak diseases, page 247. | Root-TUBERCLES Caused by Bacillus radicicola Beijerinek Locust roots often show small globose swellings. These structures are abnormal lateral rootlets which are inhabited by the nitrogen-fixing bacterium. The bacteria gain entrance to the root through the root-hairs. They multiply in the cortex cells and stimulate the tissues to over-growth. A discussion of the relation between the host and parasite will be found under alder diseases, on page 88. CHAPTER XXV MAPLE DISEASES Many species of maple occur in all parts of the United States. They are important forest-trees in the eastern and central states. Several of the native and a few exotic species are the most widely used of any trees for shade and ornament. The maples are of the genus Acer (including Negundo). In the forest the maple is seriously affected by the common white wood-rot. Other wood-rots are also occasionally found. Outside the forest, maples are subject toemany diseases which at times are important. Several species of fungi cause diseases of the leaves which may result in defoliation (see page 30). Maples are also commonly affected by sun-scorch (see page 22). The wilt disease has not been thoroughly investigated but is known to have caused the rapid death of trees in several iso- lated places. These diseases, together with the several wood- rots, account to some degree for the commonly noted poor condition of maples. Tar Lear-Spot Caused by Rhytisma acerinum Fries The large tar-like blotches on maple foliage are very con- spicuous. The leaves which develop several spots are often shed prematurely, and young nursery trees may suffer per- manent injury from defoliation. In eastern United States the red and silver maple are often attacked. In Europe the Norway and Sycamore maple are commonly affected by the same disease. In this country the Norway and Sycamore 223 224 MANUAL OF TREE DISEASES maple are rarely if ever affected, even when growing among red and silver maples which are severely infected. This sub- stantiates the results of investigations in Europe which show that there are various strains of the tar-spot fungus. These strains show preference for certain species of maples, but in other respects are indistinguishable from one another. Symptoms. The first evidence of the developing spots on the maple leaves are light green or yellowish areas. In the summer the spots become black on the upper surface of the leaf due to the black mycelium of the fungus. The surface of the tar-like spots is wrinkled with anastomos- ing furrows and somewhat raised above the surface of the leaf. The spots are usually a quarter or half inch across (Fig. 36). Cause. The tar leaf- spot of maples is caused by the fungus Rhytisma acerinum. Spores are borne free on the upper surface of the black mass of fungous tissue as it develops on the leaf. It is not known whether these spores infect other leaves or not. But from the number of leaves affected on some trees, it seems certain that these spores must account for the general prevalence of the infections. When the spotted leaves fall . Fic. 36.— Tar leaf-spot of maple. MAPLE DISEASES 225 to the ground, the mycelium inside the black spots develops ascospores. ‘These are mature in the spring. With the return of warm weather, the black layer of fungous tissue cracks open and the edges fold back, exposing the fruiting-layers within. The spores are probably shot into the air as are most ascospores. The young maple leaves are infected by the ascospores which lodge upon them and germinate. Control. Very little trouble will be experienced from this disease if the affected leaves are destroyed by burning in the autumn. Unless this is carefully done and all the affected leaves under and around the trees are destroyed, the few remaining ones may cause some infection in the spring. In exceptional cases, as in nurseries, spraying with bordeaux mixture as the leaves develop may be desirable. For general directions on spraying, see page 357. REFERENCES Stewart, F. C. Black spot, Rhytisma acerinum (Pers.) Fr. Jn Notes on New York plant diseases, 1. New York Agr. Exp. Sta. (Geneva) Bul. 328: 364. 1910. Schrenk, Hermann von, and Spaulding, P. Tar-spot. Jn Diseases of deciduous forest trees. U. S. Dept. Agr. Bur. Pl. Ind. Bul. 149:19. 1909. BLACK-SPECKED LEAF-SPOT Caused by Rhytisma punctatum Fries The silver maple of eastern United States (Acer saccharinum) and the broad-leaf maple (A. macrophyllum) of the Pacific Coast are occasionally affected by this leaf-spot. It does not seem to be as abundant as the tar leaf-spot. During the summer light green or yellowish areas about a half inch in diameter appear in the leaf. Later several isolated black spots the size of a pin-head develop on the upper surface of the spot. In the autumn the affected area remains yellowish Q 226 MANUAL OF TREE DISEASES green after the remainder of the leaf has faded or turned bright colored. The fungus causing this leaf-spot is a near rela- tive of the tar leaf-spot fungus (see page 223). Spores are de- veloped in the same manner and control measures are the same for both diseases. LEAF-SPOTS Caused by Phyllosticta minima (B. and C.) E. and E., Gleosporium apocryptum KE. and E., and other fungi The leaves of maple are subject to a number of leaf-spot diseases (see page 30). The two fungi named above are com- mon in eastern United States and may be found every year. Fic. 37.— Leaf-spot of maple caused by Phyllosticta minima. MAPLE DISEASES Pipaih Tn wet seasons defoliation may result. The illustrations show the effect of these diseases on the leaf (Figs. 37 and 38). Many of the other leaf-spots of maple appear similar to these, however, and no accurate determination can be made without a microscopic ex- -amination of the fungus. The leaf-spot caused by Phyllo- sticta minima is characterized by light brown cir- cular spots with numerous — black dot-like fruiting- bodies near the center (Fig. 37). The general char- acters of leaf- spots, and the life history of the fungi causing them, are more fully discussed on page 27. Fic. 38.— Leaf-spot of maple caused by Gleosporium apocryptum. PowpeEery MILpEws Caused by Uncinula circinata Cooke and Peck and Phyllactinia corylea (Pers.) Karst. Two species of the powdery mildew fungi are known on maple leaves in the United States, Uncinula circinata and Phyllactinia corylea (see page 35). The former has been reported from northeastern and central United States and the latter, which occurs on all kinds of trees, is distributed throughout the country. These two diseases cannot be dis- 228 MANUAL OF TREE DISEASES tinguished from one another except by the microscopic char- acters of the black fruiting-bodies which are just visible to the unaided eye. The mycelium of both fungi causes powdery white, more or less definite spots on the under sides of the leaves. The life histories and control of powdery mildew fungi are discussed on page 37. LeraFr-BLIGHT Caused by Gloeosporium sp. This leaf-blight has been observed on Norway maple (Acer platanoides) in Connecticut, New York and Virginia. No studies have been made on the disease and but little is known Fic. 39.— Leaf-blight of maple caused by Gloeosporium sp. concerning it. The leaves show yellowish and brown dead areas along the main veins (Fig. 39). Later the leaves wilt and fall from the tree. Minute brown spots form along the veins. These are the fruiting-bodies (acervuli) of the causal MAPLE DISEASES 229 fungus. The spores from these structures are disseminated by the rain. It is to be expected that perithecia with ascospores are formed in the leaves on the ground during the winter. The twigs have not been found affected. This disease is similar to the leaf- and twig-blight of sycamores described on page 333. The control measures are the same for both of these diseases. CANKER Caused by Nectria cinnabarina Fries Maples are commonly affected by this canker. Other deciduous trees may also be attacked by this disease but it never assumes great impor- tance owing to the causal fungus being only weakly parasitic. Twigs, small branches and young trees may be killed by the girdling action of the fungus. Symptoms. Small depressed dead areas of bark around wounds or branch stubs are the first evidences of the developing canker (Fig. 40). Flesh-colored or Fie. 40.— Nectria canker on pink hemispherical bodies are pro- a duced on the dead bark. Later the same pustules become chocolate-brown. If the fungus continues to spread, rolls of callus are formed around the affected area each year, until an open canker is produced which may girdle the limb. The mycelium grows most luxuriantly in the sapwood, causing a dark greenish discoloration (Fig. 41). The bark adjacent to the 230 MANUAL OF TREE DISEASES affected sapwood dies and the mycelium invades the dead bark, forming its fruiting-bodies on the outside. The canker develops Fria. 41. — Cross and longitudi- nal sections through a Nectria canker on maple. slowly and may at any time cease to enlarge. The exposed wood is then finally overgrown by the callus. This canker is especially common in severely wounded or recently pruned trees. Cause. The canker of maples is caused by the fungus Nectria cinnabarina. Spores are borne over the outside of the flesh-colored pustules during the summer. After the pustules be- come chocolate-brown, perithecia are formed which produce asco- spores. These spores are matured over winter and produce infection in wounds in the spring. Control. The cankers can be removed by surgery (see page 351). All dead bark and twigs should be cut away at the same time, since the causal fungus occurs everywhere as a com- mon saprophyte. Pruning wounds should be at once protected by a wound dressing (see page 348). REFERENCE Schrenk, Hermann von, and Spaulding, P. Nectria cinnabarina. In Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 21-22. 1909. MAPLE DISEASES 231 WILT Caused by Verticillium sp. Wilt is a recently discovered and little known disease of silver, Norway and sugar maples. It has been found in New York, Virginia and Ontario, Canada, and is probably more widely distributed. Several trees have been observed which were dying or had been killed by this disease. It seems probable that a part of the common sun-scorch of maples- may be found to be another symptom of this disease. Symptoms. In the few observations made on this disease, the common and only external symptom is the blanching and sudden wilt- ing of the foliage in midsum- mer. The leaves of an entire branch or side of the tree wilt and become dry and wrinkled at the same time. On cut- ting into the sapwood of the affected branch or trunk, the outer layers will be found more or less streaked with greenish colored longitudinal lines. No external fruiting-bodies have been found on the bark. The green discoloration extends up- ward and downward in the branches and trunk and may enter the roots (Fig. 42). Fic. 42.— Sections through the trunk of a small maple affected by wilt. Cause. The wilt of maples is due to an unnamed fungus of the genus Verticillium. Closely related species cause a similar disease, usually confined to the roots, in barberry, eggplant and numer- ous other plants. Other species of the same genus cause wilts 232, MANUAL OF TREE DISEASES of cotton, potato and various field crop plants. The fungus is known to form spores on branches of the mycelium but the manner and place of fruiting and method of infection in the maple is unknown. Control. Surgical methods are advised when this disease is to be con- trolled (see page 345). Several diseased trees in a group have been observed and the destruction of badly affected individuals is necessary to prevent the fungus spreading to healthy trees near by. Common WuitE Woop-Rot Caused by Fomes igniarius Fries Silver and striped maple are more commonly affected by this white wood-rot than the red and sugar maple. Poplar, beech and oak are the most seriously affected of the many species of deciduous trees which are susceptible to this fungus. Beech and maple in mixture in the Adirondack Mountains are often diseased to the extent that the stands will never be worth cutting. Outside the forest, this disease is not so common. The sapwood may be invaded and the tops of the trees or large limbs killed. The sporophores and decay are similar for all kinds of trees and are described under poplar diseases, page 305. Brown CHECKED Woop-Ror Caused by Polyporus sulphureus Fries Maples are at times affected by the sulfur fungus which causes the brown checked wood-rot. Oak, chestnut, walnut, butternut, locust and alder are also frequently affected by the same rot. The wood is reduced to a reddish powdery mass which splits in cubes, separated by sheets of mycelium. The sporophores of the causal fungus are orange and sulfur-yellow in color. They form from branch wounds or directly from the MAPLE DISEASES 233 bark in late summer. The sapwood and bark are often invaded and destroyed, causing the tops of the trees or large limbs to die. The symptoms of the brown checked wood-rot are simi- lar for all kinds of trees and are described under oak diseases, page 247. WuitE Strand Woop-Ror Caused by Polyporus squamosus Fries Many kinds of deciduous trees are reported as seriously damaged by this white rot in Europe. Those specially men- tioned are. maple, oak, elm, walnut, basswood, willow, ash, birch, horse-chestnut and beech. In the United States, no ‘authentic information is available on this wood-rot, except that the fungus is found in some cases growing from wounds in living trees. Symptoms. The heartwood and sometimes the sapwood of the trees are decayed. Trees in which the rot has affected the conduction tissue of the sapwood show marked decline and are often killed. The wood is characteristically rotted. It is almost white and marked with pure white narrow strands of mycelium running in the radial, tangential and longitudinal directions, causing the wood to be split into small cubes. In general this character is similar to the rot produced by Polyporus borealis in the wood of conifers (see page 185). The annual fruiting-bodies are easily recognized. They are soft and watery and almost circular with a short stout stem at one side attaching them to the tree. The top is slightly convex and is covered with overlapping brown scales, while the under surface is white and honeycombed. Cause. The white strand wood-rot of maples is caused by the fungus Polyporus squamosus; so named because of the scales 234 MANUAL OF TREE DISEASES on the top of the fruiting-bodies. It is commonly known as the scaly or saddle-back fungus. Infection is effected by the spores, which are wind-blown, lodging and germinating on exposed wood, especially at broken or pruned branch stubs. The less lignified elements of the wood-tissue are destroyed and strands of mycelium fill the long channels thus opened up in the wood. These strands run through the wood, replacing the medullary-rays and spring-wood, thus causing the white bordered cubes which are seen in cross and longitudinal sec- tions. The life history and control of the wood-rot fungi will be found discussed on page 64. REFERENCES Sechrenk, Hermann von, and Spaulding, P. White-rot caused by Polyporus squamosus. Jn Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 48-49. 1909. Buller, A. H. R. The biology of Polyporus squamosus, Huds., a timber destroying fungus. Jour. Econ. Biology. 1: 101-138, pls. 5-9, figs. A-F. 1906. Untrorm WuHitrt Sapwoop-Rot Caused by Hydnum septentrionale Fries A white sapwood-rot of maple and beech is occasionally found in eastern and central United States. This rot has not been studied and described and is not very important. The affected wood is soft and uniformly white. Brown zones separate the affected area from the normal wood. Black lines are sometimes found running in various directions in the rotted wood. The white fruiting-bodies of the fungus are very conspicuous. They are large, flat, fleshy structures often a foot or two long and a foot across. They are composed of a thick sheet of mycelium adhering to the side of the tree with numerous closely overlapping projecting shelves. The individual shelves MAPLE DISEASES 230 are three or four inches long and project two or three inches from the tree. The under surface of the shelves is composed of pendent bristles or teeth (Fig. 43). The spores are borne Sl 0 Fig. 43. — Lengthwise section through a fruiting-body of Hydnum septentrionale. over the surface of the teeth. The life history and control of the wood-rotting fungi are more fully discussed on page 64. WHITE STREAKED SApwoop-Ror Caused by Pleurotus ostreatus Jacqu. Maples and other deciduous trees, such as basswood, elm and oak, are sometimes found affected by this sapwood-rot. Infection takes place in open wounds caused by various agents. The decayed area of wood is lighter in color than the normal wood and is bounded by a narrow brown zone. The medullary- 236 MANUAL OF TREE DISEASES rays are destroyed and the porous portion of the annual rings is delignified and partially dissolved. The denser summer- wood of the rings is least affected. The result of this action is that the affected wood is light in weight and breaks easily into flakes. The sporophores of the causal fungus are fleshy, annual, shelving structures with radiating plates or gills on the under surface. ‘The sporophores are more or less sessile and appear in clusters at wounds where the affected wood is exposed. They are often found at the junction between two limbs. The upper surface is smooth, slightly rounding and white or gray- ish in color. The gills on the under surface extend on to the stalk-like attachment to the wood. For more complete details concerning the life history and control of the wood-rotting fungi, see page 64. REFERENCE Learn, C. D. Studies on Pleurotus ostreatus Jacqu. and Pleurotus ulmarius Bul. Annales Mycol. 10: 542-556, pls. 16-18. 1912. Waite Burt-Ror Caused by Fomes applanatus Fries The heartwood of the lower part of the trunk and roots of maple is sometimes destroyed by this rot. The decayed wood is whitish, light in weight and has many white-stuffed tunnels running in the horizontal direction. The sporophores of the causal fungus are shelf-like, woody bodies, with a smooth brownish upper surface and a white under surface. Further details concerning this heartwood-rot will be found under poplar diseases, on page 310. CHAPTER XXVI OAK DISEASES Over fifty species of oak (Quercus) are native in the United States. Many of these are important timber-trees. No region is without one or more species of oak, except the northern Rocky Mountains and the treeless plains. Although many kinds of oak occur on the Pacific Coast and in the Southwest, the most important forest-species grow in eastern and central United States. Many oaks are used for shade and ornament. The oak is more destructively affected by wood- and root- rots than any other important deciduous timber-tree. These diseases are also common in oaks used for ornament. Many species of fungi cause leaf-spots and powdery mildews. White oak, especially in the East, is more or less seriously affected by leaf-blight caused by the same fungus which occurs on syca- more (see page 333). This disease often results in defoliation. In the South the leaf-blister is very common and often de- structive. The twig-blight and Strumella canker described below cause the death of many oaks in the East. L&eaAFr-BLIGHT Caused by Gnomonia veneta (Sace. and Speg.) Klebahn Several kinds of oaks, especially the white oak, are attacked commonly by this leaf-blight. Sycamores (or plane-trees) are more seriously affected by the same disease. The spots de- veloped on the leaves may vary from small isolated light brown areas to large coalescing spots which involve a large portion of the leaf (Fig. 44). When the spots occur on the 237 238 MANUAL OF TREE DISEASES veins, large areas are killed and the tip of the leaf frequently dies. The dead areas become light brown and very much wrinkled. Minute darker brown pustules the size of a pin- head or smaller are scattered over the dead area. Small globules of sticky spores are developed from these pustules in rainy weather and the spores may be washed to all parts Fic. 44. — Leaf-blight of oak. of the tree, causing the infection of other leaves. The twigs are sometimes affected, but this symptom is less frequent in oak than in sycamore. The life history of the causal fungus is imperfectly known and is discussed under sycamore dis- eases, page 333. Control measures are also the same as for this disease on sycamore. OAK DISEASES 239 Lrar-BLISTER Caused by Taphrina cerulescens (Mont. and Desm.) Tulasne Practically all species of oak seem to be affected by leaf- blister. It is found throughout the United States and Europe. Although occurring commonly in this range it does no par- ticular damage except in southern United States, where it is epiphytotic in favorable seasons and defoliation results. It is re- ported that the growth of the tree is seriously im- paired and the individual is sometimes killed by repeated de- foliation. Symptoms. The blisters make their ap- pearance on the leaves before they are full grown. The spots are at first grayish or bluish on the un- der surface and yellowish above. A bulging of the leaf is soon apparent, the convex side of the spot usually being on the upper side of the leaf (Fig. 45). The blisters vary from a quarter to a half inch or more in diameter Fic. 45.— Leaf-blister of oak. 240 MANUAL OF TREE DISEASES and often become confluent, causing the leaf to curl. So far as is known, there is only the one period of infection and no subsequent spread to the other leaves of the tree occurs. Practically all the leaves of the tree may be infected, however, and where the blisters are numerous the leaves fall. Cause. Leaf-blister of oak is caused by the fungus Taphrina ceru- lescens. This fungus belongs to the family Exoascacee, all the members of which are parasitic and cause leaf-curls, leaf-blisters, plum-pockets, witches’-brooms and other types of over-growths. The common orchard disease, peach leaf-curl, is caused by a closely related form and is similar to oak leaf-blister in many ways. There are no fruiting-bodies formed by these fungi. The spores are borne in asci which stand free on the surface of the blistered or curled area. From the production of the spores which takes place as the blisters are forming, until infection occurs the next season, nothing is known concerning the life history of this entire group of fungi. No other stage of de- velopment is suspected but it is thought that the spores simply rest until the next spring and are present in some way so that they can infect the unfolding leaves. In the case of peach leaf-curl, cold wet weather following a warm period, at the time the buds are bursting, causes epiphytotics. Similar weather conditions may result in more extensive infection in the case of oak leaf-blister, but no observations are recorded on this point. | The mycelium does not enter the tissue of the oak leaf. It simply penetrates the cuticle of the lower epidermis and lies in contact with the outer walls of the epidermal cells. The enzymes of the fungus diffuse into the leaf and cause a marked reaction on the part of the leaf-tissues. The lower epidermal and spongy mesophy] cells increase in number and the palisade and upper epidermal cells increase greatly in size, causing the OAK DISEASES 241 leaf at the infected point to become much thicker. The ex- pansion of the affected area laterally, due to the increased number and size of the cells, causes it to bulge and thus the blister is formed. All the cells of the mycelium then increase greatly in size and push the cuticle off. Within each mycelial cell which is now an ascus, the spores are formed. Control. Apparently no spraying experiments of value have ever been made for the control of leaf-blister of oaks. The method used to control peach leaf-curl should be tried. It is, therefore, suggested that the trees be sprayed with bordeaux mixture 4—4-50 or lime-sulfur 1-8 at any time after the leaves fall and before the buds swell. The spraying should be thorough, since the solution must coat every twig and bud to accomplish the desired results. Peach leaf-curl is easily controlled by a single application of any good fungicide in this way. The spores must, therefore, in some way be present on the outside of the twig or bud scales and the spray mixture kills them. (See Hesler, L. R., and Whetzel, H. H. Manual of fruit dis- eases, pp.'277-283.. 1917.) REFERENCE Wilcox, E. M. A leaf-curl disease of oaks. Alabama Agr. Exp. Sta. Bul. 126: 171-187, pl. 1, figs. 1-38. 1903. (Bibliography given.) PowpEery MILpEws Caused by Microsphera alni (Wallr.) Salmon, M. alni var. extensa (Cooke and Peck) Salmon, Phyllactinia corylea (Pers.) Karst. and Erysiphe trina Harkness Four species of powdery mildew fungi (besides the brown mildew, see page 243) are known to attack the leaves of oaks in the United States. The first and third species mentioned above occur commonly throughout the country on the leaves R 242 MANUAL OF TREE DISEASES of many kinds of trees (Fig. 46). The second species is a variety of the first, seemingly confined to eastern, southern and central United States, while the fourth is so far reported only from California. All of these fungi cause powdery white patches on Fic. 46.— Powdery mildew on oak leaf. both sides of leaves, but do little damage. The black or brown- ish fruiting-bodies can be seen scattered or in clusters over the affected area of the leaf. The life history and methods of con- trol of powdery mildew fungi are discussed on page 37. OAK DISEASES 243 Brown MILDEW Caused by Spherotheca lanestris Harkness The leaves and twigs of several species of oak are often at- tacked by this powdery mildew fungus in southern, central western and extreme western United States. The mycelium grows externally on the under sides of the leaf, the spots at first being white and mealy but later appearing as a dark brown felt due to a color change in the mycelium. The entire under surface of the leaf may be covered as well as the growing twigs. When infection occurs early in the season, the brown felt may completely cover the young leaves and twigs, causing the leaves to cease growth and remain dwarfed. The black fruiting- bodies are buried in the mycelium on the under sides of affected leaves. For a fuller discussion of the life history and control of the powdery mildews, see page 37. Larce LEAF-Spot Caused by Monochetia Desmazierii Sace. The leaves of red oak are affected by the large leaf-spot in the southern Appalachians. The same disease affects chestnut leaves in that region. The spots when fully developed are very large, often being from one to two inches or more in di- ameter. ‘Two or three such spots cause the death of most of the leaf-tissue. The center of the spot is pale green or yellow and is surrounded by concentric bands of red and brown. The colored bands are less distinct on the under surface of the leaf. Small black fruiting-bodies, arranged in clusters, dot the affected area. The spores from these fruiting-bodies cause the infection of other leaves. Fuller details concerning this disease are given under chestnut diseases, page 139. Many other leaf-spots occur on oak. A general discussion of the leaf-spots will be found on page 27. 244 MANUAL OF TREE DISEASES Twic-BLIGHT Caused by Spheropsis malorum Berkeley (= Physalospora cydonie Arnaud) This twig-blight is common on chestnut oak in central eastern United States. White oak and chestnut are also oc- casionally affected by the same disease. The smaller branches and twigs of trees of all ages may be killed. Symptoms. The leaves wither and turn brown. The mycelium of the causal pathogene grows in the bark and sapwood. The diseased bark becomes sunken and wrinkled (Fig. 47). Small black fruiting-bodies break through the outer bark. Under the dead bark, the sapwood is dark colored. The mycelium extends for several inches in the sapwood above and below the bark-lesion. This is evident to the unaided eye as a black streak when the bark is peeled from the twig. Cause. The fungus causing this twig-blight is known as Spheropsis malorum. It occurs as a weak Twig-cankeron Parasite or saprophyte on the bark and twigs of oak caused by many kinds of woody plants. The New York plas ™ apple canker, black-rot and frog-eye leaf-spot of apple are caused by this fungus. Spores ooze from the black fruiting-bodies produced on the dead bark and may be washed by the rain to other parts of the tree. The fungus also rarely produces a perithecial stage which is known as Physalospora cydome. OAK DISEASES 245 Control. The diseased twigs and branches should be pruned from the tree. This may be done most efficiently in midsummer, as the dead leaves show more plainly. Early the next spring after the new leaves appear, all leafless twigs and branches should be removed. If these measures are not taken, large trees may often be killed after a few years. Care should be exercised to prune the twigs at least six inches below the cankered area, since the mycelium which spreads in the sapwood must all be removed (see under symptoms). REFERENCE Ingram, Della E. A twig blight of Quercus prinus and related species. Jour. Agr. Res. 1: 339-346, pl. 38, figs. 1-7. 1914. STRUMELLA CANKER Caused by Strumella coryneoidea Sace. and Winter This canker of oak has been found to be common and de- structive in Pennsylvania. Although not definitely reported elsewhere, the fungus is known to occur in Missouri, Massa- chusetts and New York. Its range may thus be supposed to include northeastern United States. In Pennsylvania the canker is found on white, scarlet, red, yellow and chestnut oak. It also occurs destructively on the American chestnut. The most damage is reported on red and yellow oak. Symptoms. Two types of cankers with intermediate gradations are de- scribed. The most conspicuous form is found on red and yellow oak and resembles the European apple-tree canker, caused by Nectria galligena. The development of the cankers of this type is slow. They are elliptical in outline and consist of a depressed decayed center surrounded by concentric folds 246 MANUAL OF TREE DISEASES of callus. The tissue around the canker is irregularly swollen, causing badly deformed trunks. The cankers gradually girdle the trunk and the trees are either blown over or die. Suckers are formed in abundance just below the cankers. On young smooth-barked trunks, another type of canker is formed which is at first a light yellow- ish raised area of bark and later develops into a sunken dead surface which quickly girdles the stem. When the bark is peeled from these cankers, thin sheets of white or pale brownish mycelium are exposed. On the surface of the affected bark of both types of cankers are numerous small black nodules which are the fruiting-bodies of the causal fungus. Cause. This canker of oaks and chestnut is caused by the fungus Strumella coryneoidea. No ascus stage has been found con- nected with this species and it is known only by the conidial fruiting-bodies. Inoculations have not been made with this fungus to determine fully its pathogenicity. The fungus is found invariably associated with the cankers and has been isolated and grown in pure culture. The black nodules on the cankers which have not girdled the trunk do not produce spores and are abortive. As soon as the trunk is girdled, however, nu- merous brownish powdery pustules burst through the bark. ° The spores of the fungus are borne free on the surface of these pustules and are believed to be carried by the wind. The mycelium penetrates the wood deeply and causes a weakening of the trunk. Infection usually occurs through a small branch stub and from this center the mycelium spreads in all directions. Control. No definite control measures are suggested for this canker. The ordinary surgical methods of canker treatment, however, OAK DISEASES 247 will apply (see page 351). Care must be taken to remove the affected wood beneath the cankered area or the mycelium may spread into the healthy bark. REFERENCES Heald, F. D., and Studhalter, R. A. The Strumella disease of oak and chestnut trees. Pennsylvania Dept. Forestry Bul. 10: 1-15, pls. 1-12.. 1914. Buckhout, W. A. The undesirability of red and black oak because of fungus disease. Pennsylvania Agr. Exp. Sta. Ann. Rept. 1899: 250-252. 1900. Brown CHECKED Woop-Rot Caused by Polyporus sulphureus Fries This important wood-rot is commonly found throughout the United States in oak, chestnut, maple, walnut, butternut, lo- cust and alder. It has also been reported in white spruce in Maine. In Europe this disease is important in certain conifer as well as deciduous trees. Although not as destructive in the forests of the Northeast as some other diseases, it is the most common wood-rot of shade and ornamental oaks. The sap- wood and bark are affected and the tops of trees and large limbs are killed when thus girdled. The causal fungus lives saprophytically in all kinds of timber. Symptoms. The characters of the decay caused by the sulfur fungus serve readily to identify it, even in the absence of the yellow sporophores. The heartwood is usually first to be decayed. Gradually, however, the sapwood and bark are invaded and the living cells of these tissues are killed. The more com- pletely decayed wood is often bordered by a wide slightly dis- colored zone. The decayed wood becomes reddish brown and has the appearance of charcoal except in color. It is easily re- duced to powder by a blow. In the process of shrinkage which 248 MANUAL OF TREE DISEASES accompanies the decay, the affected wood splits into cubes by radial and circumferential cracks. The mycelium then grows into and fills the cracks and forms tightly woven sheets (Fig. 48). Fic. 48.— Brown checked wood-rot in oak. The sporophores of the sulfur fungus are easily recognized. They emerge in late summer from old branch wounds or di- rectly from the bark where the mycelium has decayed the sapwood. At first they appear as one large or several small sulfur-yellow, soft and watery knobs of mycelium. These OAK DISEASES 249 quickly grow larger and form a number of individual or closely over-lapping shelves, from one to several inches wide (Fig. 49). The upper surface of the shelves is bright orange-yellow marked with redder areas, while the under surfaces are sulfur-yellow and ap- pear honeycombed. Thesubstance of this mature fruiting-body is tough but very watery. Insects rapidly invade it and_ through their work and decay caused by bacteria and possibly other fungi, the fruiting-body is quickly de- stroyed. What remains of it soon dries and becomes white and brit- tle. The mycelium in the wood lives from year to year and pro- duces these yellow sporophores annually. The young sporophores, collected before the shelves are fully matured, are among the best of the edible fungi. Cause. Brown checked wood-rot is caused by the fungus known as Polyporus sulphureus. The spores from the tubes on the under sur- face of the sporophores are wind- blown and infect the exposed heartwood at branch wounds. of Sie 2 Beles os Fia. 49.— Fruiting-bodies of Poly- porus sulphureus on an oak. Certain deposits left by the mycelium of the fungus cause the reddish brown discoloration. For further details con- cerning the life history and control of the wood-rot fungi, see page 64. 250 MANUAL OF TREE DISEASES REFERENCES ON Brown CHECKED Woop-Rot Schrenk, Hermann von, and Spaulding, P. Red heart-rot caused by Polyporus sulphureus. Jn Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 37-39. 1909. Schrenk, Hermann von. Polyporus sulphureus (Bull.) Fr. Jn Some diseases of New England conifers. U.S. Dept. Agr. Div. Veg. Phys. and Path. Bul. 25: 40-44. 1900. Atkinson, G. F. Polyporus sulphureus. Jn Studies of some shade tree and timber destroying fungi. Cornell Univ. Agr. Exp. Sta. Bul. 193: 208-214, figs. 64-70. 1901. Hartig, R. Polyporus sulphureus Fr. Jn Die Zersetzungserschei- nungen des Holzes ete., pp. 109-113, pl. 14. 1878. Common Wuite Woop-Rot Caused by Fomes igniarius Fries Oaks, especially those species belonging to the black oak group, often are found with the heartwood reduced to a white punk. Beech and poplars, especially the aspen and balm of Gilead, are the most destructively and commonly affected of the various kinds of deciduous trees attacked by this fungus. In Europe this is the most important of the wood-rots of the oak in the forest. In the United States, the brown checked wood-rot of oak seems to be more destructive. This is es- pecially true outside the forest, where shade and ornamental oaks are concerned. The sapwood of oak is more commonly invaded than is the sapwood of the other trees affected, re- sulting in stag-head and dead limbs. The sporophores and nature of the rot which are similar for all kinds of trees are described under poplar diseases, on page 305. Wuite Pocker HEartwoop-Rot Caused by Polyporus Rheades Fries (= Polyporus dryophilus Berkeley) The heartwood of many species of oaks and sometimes of poplars, is destroyed by this disease. Although found in oaks practically over the entire United States, this rot is particu- OAK DISEASES DAS larly destructive and common in the Southwest and along the Pacific Coast. In poplar it is found rarely and then often fol- lowing the common white wood-rot caused by F. igniarius. The white pocketed rot of the heartwood of oaks is confined largely to the upper portions of the larger and older trees. Symptoms. The first evidence of this rot in oaks is a discolored water- soaked area in the heartwood. Later delignification results in the medullary-rays turning white. In longitudinal section this produces a mottled appearance of white irregular lines running lengthwise and broader white areas joining these at intervals. The wood between these white areas is slightly dis- colored. In more advanced stages, the white areas involve adjacent tissues and become more extensive and less definitely linear. The small amount of discolored wood between the white areas remains firm. Irregularly distributed in the de- cayed wood are brown areas varying from an eighth to a half inch across. The wood surrounding the white pocketed surface is discolored and water-soaked. In some species the symptoms vary slightly from those described above. In chestnut oak the spring-wood of the annual rings is yellowish white ‘and the tissue between these concentric zones is light brown. In poplar the rot as seen in cross-section produces alternate zones of whitish and yellow tissue. ‘The same brown areas are present as in the oak. The sporophores formed at branch wounds on the oaks are flat and shelf-like or hoof-shaped, but when formed directly from the bark they are almost globose. A peculiar diagnostic character of these sporophores consists in a hard, granular sandstone-like core with radiating white mycelial strands run- ning through it. This core extends back into the rotted wood of the tree for a short distance. The upper surface is rusty yellow or brown and at first is hairy but later becomes smooth. 252 MANUAL OF TREE DISEASES The under surface is brown as is the inside structure, including the granular core. Cause. The white pocketed rot of oaks and poplars is caused by the fungus Polyporus Rheades which is also known by the name P. dryophilus. The sporophores described above are annual. The rot may be confined largely to the branches and upper part of the trunk or the tree may be rotted from the base to top. Infection occurs most commonly in broken branches, from which the mycelium extends down into the trunk. When in- fection takes place through dead side branches or at the base of the tree, through fire scars, the rot may extend the entire length of the trunk. For fuller details concerning the life history of wood-rot fungi and the nature of the decay caused by them, see page 64. REFERENCES Hedgecock, G. G., and Long, W. H. Heart-rot of oaks and poplars caused by Polyporus dryophilus. Jour. Agr. Res. 3: 65-80, pls. 8-10. 1914. Schrenk, Hermann von, and Spaulding, P. Piped-rot of oak and chestnut. Jn Diseases of deciduous forest trees. U. 8. Dept. Agr. Bur. Pl. Ind. Bul. 149: 39-40, pl. 5. 1909. (Note: The piped-rot of oak described is due to P. Rheades and that of chest- nut to P. croceus.) Hartig, R. Polyporus dryadeus Fr. Jn Die Zersetzungserschei- nungen des Holzes ete., pp. 125-128, pl. 17. 1878. (This is a discussion of the rot due to P. Rheades and not P. dryadeus.) Strinc AND Ray Burt-Rot Caused by Polyporus Berkeleyi Fries This heartwood-rot of the base of oak trees is found through- out eastern and central United States. It is not known to be as common or destructive as several of the other wood-rots of oaks. Mature and over-mature trees are affected. It is never found in the tops of trees but is limited to the base of the trunk OAK DISEASES 253 and the larger roots. The decay extends from the surface of the ground upward in the heartwood for a distance of one to a few feet and in its final stages leaves a large hollow cavity. Symptoms. When badly rotted trees are cut, they fall after the thin shell of heartwood is cut through and the trunk carries with it the partially rotted hollow cylinder of wood from the stump. The odor of the freshly cut rotted wood is very strong and resembles anise oil. The first indication of the decay is seen in longi- tudinal section as a yellowish or whitish area from four to eight Fie. 50.— Fruiting-body of Polyporus Berkeleyi. inches long. The summer-wood in this region is delignified and the individual fibers are separated by the dissolving of the cementing layer between them. As the decay progresses the dense whitish summer-wood is completely destroyed. This leaves the medullary-rays and strands of porous spring-wood intact. The interwoven rays and strings of wood are brownish at first but soon are covered with whitish mycelium. The strands slowly become more brittle and finally collapse, leaving a hollow cavity. The decayed area becomes larger and is bordered by a zone of whitish wood with the string and ray rot stage projecting into the hollow cavity. The sporophores arise from the exposed larger roots or may 254 MANUAL OF TREE DISEASES appear to come from the soil near the base of the tree. In ail cases, however, they will be found attached by mycelial strands to the roots. The sporophores are usually large and may occur as two to five overlapping shelves or as a single more or less circular, expanded, toadstool-like body supported on a thick stalk (Fig. 50). The center of the upper surface is depressed where it is attached to the stalk. The upper surface is white or yellowish, while the under surface is whitish and covered with large angular honeycomb-like pores. Cause. The string and ray butt-rot of oaks is caused by Polyporus Berkeleyi. The spores are borne around the inner surfaces of the angular pores of the sporophores. Infection takes place in wounds at the base -of the tree, such as fire-scars. The life history and control of wood-rotting fungi are discussed more fully on page 64. REFERENCE Long, W. H. Three undescribed heart-rots of hardwood trees, espe- cially of oak. Jour. Agr. Res. 1: 109-128, pls. 7-8. 1913. Wet Heartwoop-Ror Caused by Hydnum erinaceus Fries Oak and other deciduous trees are affected by this wet heart- wood-rot. White and red oaks are most commonly affected. The disease is common in central United States and is some- times found in other parts of the country. Symptoms. In the early stages of this decay, the wood becomes lighter in color and the woody tissue between the medullary-rays is destroyed. Later the entire structure of the wood disappears and there remains only a white soggy mass. Large cavities OAK DISEASES 255 or entirely hollow trees are thus formed. The cavities are filled or lined with yellowish mycelium. The fruiting-bodies of the causal fungus are formed annually at wounds or insect tunnels. They are globose and may be as large as a foot across. The upper surface is hairy and covered with drops of water. The under surface and the margin of the fleshy fruiting-body are covered with numerous long pendent spines or teeth. Insects soon destroy the fruiting-body. Cause. The wet heartwood-rot of oaks and other trees is caused by Hydnum erinaceus. The spores are borne over the outer sur- face of the teeth on the under side of the fruiting-body. They are disseminated by the wind and infection takes place in wounds of all sorts. Further details concerning the life history and control of wood-rots will be found on page 64. REFERENCE Sehrenk, Hermann von, and Spaulding, P. Disease caused by Hydnum erinaceus. Jn Diseases of deciduous forest trees. U. S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 44-45, pl. 7. 1909. Honetycoms HrEartwoop-Rot Caused by Stereum subpileatum Berkeley and Curtis This heartwood-rot of oak is common in Arkansas, Missis- sippi and Louisiana. It is also found in Kentucky, Ohio, Missouri, Virginia and Florida and probably is generally dis- tributed over southern United States. Several species of oaks are affected. The sapwood is not destroyed and the sporophores of the fungus occur only on dead fallen trees or on dead areas in living trees. Symptoms. The affected wood is at first slightly discolored and water- soaked. Light colored areas appear at various places in the 256 MANUAL OF TREE DISEASES discolored region and develop into white pockets. They are located partially in the porous spring-wood of one ring and in the summer-wood of the adjoining ring. Later the pockets become hollow and have a white lining. They become larger in time until finally limited by reaching a large medullary- ray on each side. Only a narrow layer of brownish wood separates the adjoining pockets. In longitudinal sections, the pockets are seen to be from three to five times as long as wide. The discolored area extends from one to six feet beyond the region showing the pockets. In the first stages of the decay, this rot closely resembles the white piped butt-rot caused by Polyporus croceus (see page 258). The latter rot usually ex- tends its activities more rapidly upward than radially, causing the decay of a few annual rings, while the honeycomb-rot in white oak, at least, spreads uniformly in both directions. Freshly cut wood affected by this rot is said to have the odor of old honeycomb. The sporophores are rarely available to identify this rot in living trees, except when a large area of the affected heartwood is exposed. Sporophores develop on the felled timber in a year or two and continue to form for several years. They are from a quarter of an inch to two inches wide, rather thick shelving bodies occurring one over the other in long rows. The upper surface is at first downy and light yellowish brown, later becoming smooth and gray. Concentric furrows mark the upper surface into zones which vary in color. The under surface is light yellowish brown and smooth. Cause. The honeycomb heartwood-rot of oaks is caused by the fungus, Sterewm subpileatum. The fruiting-bodies described above are annual structures which become dry and _ persist through the winter and may revive the following season. The spores are borne over the entire smooth under surface of the OAK DISEASES ALS shelves. The fungus finds entrance into the tree where heart- wood is exposed at fire-scars, branch wounds and the like. While usually found in the base of the trees, it sometimes oc- curs in the tops. The sapwood of the living tree is not affected, but when the tree is felled the mycelium grows into the sapwood and causes a similar decay. Control. In the forest this rot can be controlled by preventing fires, which are responsible for the scars that furnish a ready en- trance point for infection. Likewise it is essential to remove or burn dead and diseased oaks that are standing, as well as cull logs, for on these the sporophores will continue to form for several years. These measures will also keep several of the other butt-rots and heartwood-rots of oaks under control. REFERENCE Long, W. H. A honeycomb heart-rot of oaks caused by Stereum sub- pileatum. Jour. Agr. Res. 5: 421-428, pl. 41. 1915. Sorr Hrartwoop-Rot Caused by Polyporus obtusus Berkeley Black oaks in eastern and central United States are affected by this heartwood-rot. Several trees are usually found affected in a group where the disease occurs. Symptoms. The affected heartwood is lighter in color than the normal wood and finally becomes almost white. The wood does not check and retains its normal fibrous character. It, however, is weak and breaks easily. The rot progresses rapidly and the trunks are weakened so that they snap off during wind-storms. The fruiting-bodies appear annually on the side of the trunk. They are more or less hoof-shaped and at first white and spongy. S 258 MANUAL OF TREE DISEASES Later they become yellowish or brown. The upper surface and the rounded edge and outer margin of the lower surface are hairy. The remainder of the under surface is covered with roundish or sinuous pores, the edges of which are irregular, making the under surface rough. Cause. The soft heartwood-rot of black oaks is caused by Polyporus obtusus. The spores borne within the tubes on the under sides of the fruiting-bodies are blown about by the wind. Infection usually takes place by the spores entering the tunnels made in the wood by the insect, Prionoxystus robinia. From the tunnels the mycelium spreads upward and downward in the wood. The fruiting-bodies are usually produced at the insect burrow where infection occurred. For further details con- cerning the life history and control of wood-rot fungi, see page 64. REFERENCES Spaulding, P. A disease of black oaks caused by Polyporus obtusus Berk. Missouri Bot. Garden Rept. 16: 109-116, pls. 13-19. r eine Hermann yon, and Spaulding, P. Soft rot of oaks caused by Polyporus obtusus. Jn Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149 : 41-42, fig. 5. 1909. Waite Pirep Burr-Rotr Caused by Polyporus croceus Fries (= P. Pilote Schw.) This wood-rot is found in oak and chestnut. The wood of the roots and base of the trunk is most commonly affected, although when dead branches are common it may be found in the upper part of the trunk. It has proved destructive in Arkansas, Virginia and New York and probably is generally distributed throughout eastern and central United States. The decayed wood is at first filled with white areas which en- OAK DISEASES 259 large and become hollow cavities with white margins. These pockets become so abundant that the summer-wood is largely converted into strings of white fibers leaving the wood brittle and easily broken. Further details concerning this white pocket- or piped-rot will be found under chestnut diseases, page 150. Straw-CoLoreD Butt-Ror Caused by Polyporus frondosus Fries This rot of the heartwood of the base of oak and probably of chestnut is found in eastern and central United States but does not seem to occur very commonly or destructively. It develops only in the base of the trunk. The wood is not en- tirely destroyed and the trees do not become hollow. Symptoms. In longitudinal section the upper advancing margin of the decay is indicated by long, slender, white lines extending for several inches upward into the sound wood. In advance of the white lines, the wood is water-soaked and reddish in color. The rotted wood is at first white and later tan- or straw-colored. Most of the tissue is delignified but is firmly held together by the less affected medullary-rays. The cut ends of the trunks of felled trees become reddish brown after a month or two. The sporophores of the causal fungus arise from exposed or buried roots near the base of the tree. They are composed of a fleshy stem which is much branched, the ends of the branches forming small flat over-lapping shelf-like structures. The whole fruiting-body is more or less globose. The upper surfaces of the shelves are gray or drab and the under surfaces white. Cause. The straw-colored butt-rot of oak is caused by Polyporus frondosus. The spores from inside the tubes on the under sides 260 MANUAL OF TREE DISEASES of the shelves of the fruiting-body cause infection in wounds at the base of the tree. The life history and control of the wood- rot fungi will be found discussed on page 64. REFERENCE Long, W. H. Three undescribed heart-rots of hardwood trees, espe- cially of oak. Jour. Agr. Res. 1: 109-128, pls. 7-8. 1913. Waitt Woop-Rot Caused by Fomes Everhartii (Ellis and Gall.) Sechrenk This wood-rot has been found common in black jack oak and probably occurs in other species. It has not been fully de- scribed. It is said to resemble closely the common white wood- rot caused by Fomes igniarius. ‘The rot extends into the sap- wood. The sporophores of the causal fungus also resemble those of Fomes igniarius. They are shelf-like and rarely hoof- shaped. The upper surface is at first brown, but later becomes black and checked by many fissures. The under surface and margin are brown. The pores in the under surface are very small. REFERENCE Schrenk, Hermann von, and Spaulding, P. Heart-rot of oaks caused by Fomes Everhartii. Jn Diseases of deciduous forest trees. U.S. Dept. Agr. Bur. Pl. Ind. Bul. 149: 48, pl. 3. 1909. Waite Burt-Rotr Caused by Fomes applanatus Fries The heartwood of the lower part of the trunk and roots of oak is sometimes destroyed by this rot. The wood becomes whitish and light in weight but retains its fibrous structure. The rotted wood when split shows numerous sinuous white- stuffed tunnels resembling the work of insects. The sporo- phores of the causal fungus are often found at wounds near the OAK DISEASES 261 base of the trunk. The form on oak is usually thick, with a dark gray, rough upper surface, an acute margin and a slightly roughened, white under surface. This heartwood-rot is more fully described under poplar diseases, on page 310. WuitEe Root-Ror Caused by Polyporus dryadeus Fries Many species of oaks are affected by a white root-rot which occurs apparently throughout the range of the oaks in the United States and Europe. Although not as important as many of the other wood- and root-rotting fungi, oaks growing under adverse conditions are often found affected. The ulti- mate result of the attack is the death of the tree or it may be uprooted during wind-storms. Symptoms. The first indication of the rot is a reddish or brownish colora- tion of the inner bark-tissues. The adjacent sapwood then be- comes reddish brown and watery. The discoloration advances -into the wood and the color of the decayed areas changes to white. The bark becomes loosened and shreds into strips. The rot finally involves the larger roots and extends into the butt of the tree but does not progress above the surface of the ground. The smaller roots are completely decayed and look like pith. They are light in weight and when twisted break into concentric layers. Older partially decayed roots, in longitudinal section, show the white or cream-colored rotted bark and wood bounded by a dark brownish zone one to three inches wide which marks the progressing area of change from normal wood to white punk. The radial and longitudinal whitish bands appearing in the affected wood are due to the mycelium of the fungus which is aggregated in the porous regions of the annual rings. White patches of mycelium ap- 262 MANUAL OF TREE DISEASES pear on the surface of the outer bark of affected roots. The largest roots may be rotted to the center and the decayed wood is finally spongy and easily crushed. The sporophores of the causal fungus form on exposed roots when the tree is blown over or at the very base of the trunk, arising at the surface of the ground. They are large, irregu- larly shaped masses of a corky or woody texture (Fig. 51). When developing, they are watery, and large drops of water Fig. 51. — Fruiting-body of Polyporus dryadeus. often form on the outer growing margin. These drops leave depressions in the surface. The upper surface is uneven and light brown, changing with age to darker brown and black. The under part is oblique to the surface of the ground in the thicker forms and more or less horizontal in the thinner forms. The pores in the under surface are soon stuffed with mycelium, making them invisible. The outer margin of the sporophore is thick and rounded. In- sects soon destroy the under surface and outer margin but the OAK DISEASES 263 black partially rotted central mass may remain for years at- tached to the root or trunk. Cause. The white root-rot of oaks is caused by the fungus Polyporus dryadeus. The sporophores are rarely found but the rot is not uncommon. The method of infection has not been described. No fungous strands are found in the soil around the rotted roots, as in the shoe-string root-rot, and the trees apparently are not attacked in groups. The spores produced in the tubes of the sporophore probably find lodgment on exposed roots and thus initiate infection. The mycelium grows first in the bark and then into the sap- wood and heartwood. The brownish watery zone of the first stage of decay is due to the production of a brownish liquid which fills the cells. Later this disappears and the cell con- tents and a portion of the cell-walls are dissolved. There is little delignification, although the wood appears white. The ease with which the wood splits into concentric rings and frac- tures crosswise is due to the very thin walls left in the porous part of the annual ring and medullary-rays. The tree suffers general decline because of the destruction of the conducting tissue of the roots and they may be killed outright when the larger roots are attacked first. REFERENCE Long, W. H. Polyporus dryadeus, a root parasite on the oak. Jour. Agr. Res. 1: 239-250, pls. 21-22. 1913. CHAPTER XXVII PINE DISEASES Over thirty species of pine (Pinus) occur as forest-trees in the United States. No region of the country where trees grow is without representatives of this important group. A large part of the timber of the country is made from pines. The various native pines and many exotic species and varieties are used for ornamentals. Pine is subject to many destructive diseases wherever it grows. The most important of these are root-rots, wood-rots, blister-rusts, mistletoe injury, leaf-cast and various types of winter-injury. The importance of these types of diseases varies with the species and region of the country in question. Pecky wood-rot and the different blister-rusts of the branches and trunks probably cause the most damage. The white pine of the northeastern states was reasonably free from important diseases until the introduction from Europe of the blister-rust fungus. Pines outside of the forest often suffer severely from winter-drying and other types of injury due to extremes in temperature. SEEDLING Root-Ror Caused by Rhizina undulata Fries The seedlings of several species of pines in the forests of northwestern United States are killed by this root-rot. The fungus is also present in several eastern states and may cause similar damage. The roots cf seedlings three to six years old are killed. Examination shows the. roots and a quantity of 264 PINE DISEASES 265 soil to be matted together by white mycelium. Brown fruiting- bodies are formed on the surface of the soil around diseased trees. This fungus is more fully discussed under hemlock diseases, page 177. Lear Buister-Rvusts Caused by fungi of the genus Coleosporium Several species of the genus Coleosporium grow in the needles of pines, occasionally causing defoliation. These rust-fungi require, in addition to the pine, some other kind of plant on which to continue their life history. Such an alternation of hosts is not uncommon in the rust-fungi. In the case of the Coleosporium leaf-rusts of pine, «ciospores are produced in the yellow blisters pushed out from the pine needles. These spores cannot reinfect the pine, but they may cause infection of the leaves of certain near-by flowering plants. Here the development of the fungus is continued and_ urediniospores are formed. The urediniospores infect other plants of the same kind and by a succession of several generations of these spores the rust may become prevalent during the summer for a considerable distance away from the pine which developed the eciospores. In the autumn a brown layer of another type of spores (teliospores) is formed on the plants which produced the urediniospores. The teliospores germinate while they are still attached to the host and minute basidiospores are formed. These spores are short-lived and are blown about by the wind. If they come into contact with the needles of the proper species of pine, they may initiate a new infection. Thus the seasonal life history of the fungus is completed. By eliminating the flowering plant, which must be present for the fungus to complete its development, the rust is incapable of existing. The minimum distance for the successful inter- change of spores between the pine and the alternate host is variable. Control is sometimes accomplished when all the 266 MANUAL OF TREE DISEASES flowering plant hosts are removed, so that none exists within a thousand feet of the pines. A safer distance would be a quarter or a half mile, depending on the contour of the land and the nature of the surrounding vegetation. The elimina- tion of all the plants of the kind required by the blister-rust fungi is not easily accomplished. Nevertheless, it is an efficient and sure method of control, if the eradication is thoroughly done. For a further discussion of the factors involved in carry- ing out eradication methods, see under blister-rust of five- needle pines, page 274. Many of the species of Coleosporium that are known in the uredinial and telial stages on various weed plants have not been connected with the blister-rust stage on pine needles. Either this has not been found and described, or the relation between the stages on the pine and weed host has not been definitely proved to represent the life history of a single species. When all the stages are known, the fungus is called by its Coleosporium name. When only the blister-rust stage is known on the pines, it is classified in the large form genus Peridermium and is given a temporary specific name. Below are given brief descriptions of the blister-rusts of the needles of pines, with their distribution, the species of pine affected and the alternate weed hosts, so far as these facts are known. In most cases these blister-rusts cannot be identified except by microscopic examination. An inconspicuous blister-rust is known to occur in Maryland on scrub pine. The name of the causal fungus is Coleosporium inconspicuum (Long) Hedgeock and Long. The alternate weed- hosts on which its life history is completed are the tickseeds (Coreopsis verticillata and C. major). Scotch pine needles are affected by Coleosporium sonchi- arvensis (Persoon) Lev. This disease has been reported only from Wisconsin. The fungus was imported from Europe. The yellow blisters are small, being about one-sixteenth of an PINE DISEASES 267 inch long or smaller and only project slightly above the surface of the needle. The life history is completed on the sow thistles (species of Sonchus). A blister-rust of the needles of lodge-pole and western yellow pine is caused by Peridermiwm montanum Arthur and Kern. It is known from central Montana westward and northward. The yellow pustules on the pine needles are about one-sixteenth of an inch long and project only slightly above the surface of the needle. The alternate weed hosts are probably the differ- ent species of Arnica. A blister-rust of the needles of short-leaf pine is caused by Peridermium intermedium Arthur and Kern and is known from central Missouri and Arkansas to central North Carolina. The yellow pustules on the needles are from one-sixteenth to one-eighth of an inch long and project above the surface of the needle about one-sixteenth of an inch. The alternate weed host has not been determined. A conspicuous leaf blister-rust is known on loblolly, long-leaf, sand, short-leaf, spruce, western yellow, pitch, pond and Cuban pines. The causal fungus is Coleosporium vernonie B. and C. (=C. elephantopodis (Schw.) Thiim.) and is found from Vir- ginia to Florida and westward to central Texas. The yellow pustules on the needles are larger than those of the other pine leaf blister-rusts. They are about one-fourth of an inch long and three thirty-seconds of an inch high. The alternate weed hosts of this rust are different species of ironweed and elephant’s- foot (Vernonia and Elephantopus). A leaf blister-rust of pitch and Norway pine is caused by Coleosporium solidaginis (Schw.) Thiim. and is known from Massachusetts and central New York southward to central North Carolina.. Although the disease has been found only within the above indicated area, there is the possibility of its appearance on pitch and Norway pine at almost any point in North America, since the stages of the causal fungus on the alter- 268 MANUAL OF TREE DISEASES nate weed hosts are found throughout the country. This rust is similar to several other blister-rusts which affect the pitch pine. The yellow pustules project above the surface of the needles from one thirty-second to cne-sixteenth of an inch. The alternate weed hosts are species of goldenrod and wild aster. The rust is able to maintain itself on these weeds without the presence of the pitch pine, by the wintering-over of the ure- diniospores which reinfect the goldenrod and aster. A prominent leaf blister-rust of pitch pine is caused by Cole- sporium campanule (Persoon) Ley. and is known from New Jersey and central Indiana southward to central North Caro- lina. It differs from the other blister-rusts of pitch pine in that the yellow pustules on the needles are much larger and tongue- shaped. They are from one-sixteenth to one-eighth of an inch long and project above the surface about one-sixteenth of an inch. The alternate weed host is the tall bellflower (Cam- panula americana). Another blister-rust of pitch and Norway pine is caused by Coleosporium delicatulum (Arthur and Kern) Hedgecock and Long. It is found along the Atlantic coast from Massachusetts to Florida. It may have a much wider range than this, since its alternate stages on the weed host, species of Euthamia, have been found from Maine to Kansas and southward to West Virginia and Texas. The leaves of the pines show in the spring very small yellow blisters, from one thirty-second to one-fourth inch long and scarcely protruding above the epidermis of the needle. Short-leaf, long-leaf, pitch and loblolly pine are affected by a needle blister-rust in central eastern and southeastern United States, caused by Coleosporium ipomee (Schw.) Burrill. The pustules on the pine needles are flattened, narrow and about one-sixteenth of an inch long. The life history is completed on many species of merning-glory (Ipomeea). Short-leaf and loblolly pines in Georgia and North Carolina PINE DISEASES 269 have been affected by a needle blister-rust caused by Coleo- sporitum terebinthinacee (Schw.) Arthur. The pustules are tongue-shaped and project about one-sixteenth of an inch from the needles. The life history of this fungus is completed on rosin-weed (species of Silphium). The needles of scrub and probably of short-leaf pine from Pennsylvania to Illinois and southward are attacked by Coleo- sporium helianthi (Schw.) Arthur. The blisters are tongue- shaped and project from the leaf about one-sixteenth of an inch. The life history of the fungus is completed on sun-flower (Heli- anthus). The needles of long-leaf, loblolly and pitch pine are attacked by Peridermium fragile Hedgecock and Hunt. The blisters are narrow and inconspicuous. The alternate host for the com- pletion of the life history of this fungus is not known. In Florida the needles of loblolly and spruce pine are attacked by Peridermium minutum Hedgeock and Hunt. The blisters are low and a little narrower than long. The alternate host for the completion of the life history of this rust is unknown. The needles of pifon are attacked by Coleosporium ribicola (C. and E.) Arthur, practically throughout the range of this species in Colorado, New Mexico and Wyoming. The blisters appear on the pine needles while snow is still present. The alternate hosts of this fungus are species of currant and goose- berry (Ribes). The pustules on the currant and gooseberry leaves are larger and more prominent than the felt-rust (see page 274). REFERENCES Arthur, J. C., and Kern, F. D. North American species of Perider- mium. Bul. Torrey Bot. Club, 33: 403-488. 1906. Arthur, J. C., and Kern, F. D. North American species of Perider- mium on pine. Mycologia 6: 109-138. 1914. Hedgecock, G. G., and Hunt, N. Rex. New species of Peridermium. Mycologia 9: 239-242. 1917. Hedgecock, G. G. Notes on some western Uredineew which attack forest trees. Mycologia 4: 141-147. 1912. 270 MANUAL OF TREE DISEASES Lear-Rust Caused by Gallowaya pini (Galloway) Arthur The leaves of scrub pine are commonly affected by this rust throughout its range in central eastern United States. This disease differs from the blister-rusts of pine needles in the teliospores being borne on the pine and no alternate host being required (see page 265). Yellow spots occur near the tips of the leaves. On these spots are formed linear, reddish orange pustules which burst through the epidermis. These pustules may be a half inch long. The bright color soon fades and they are inconspicuous. The teliospores germinate in the spring, producing basidiospores which infect other scrub pine needles. LeEaF-Cast oF WHITE PINE Caused by Hypoderma strobicola Tubeuf White pine is sometimes injured in eastern United States by this leaf-cast. Pitch pine and hemlock are reported to be affected by the same disease. The affected needles at first show yellowish spots and later turn reddish yellow and brown. The tissues of the twig may also be killed. Later in the season several small elliptical black fruiting-bodies appear on the outer surface of the needles. The fruiting-bodies are mature the following spring. They split open and the spores are shot into the air during prolonged rain periods. For further details concerning the leaf-cast diseases, see page 38. REFERENCES Graves, A. H. Leaf blight. Lophodermium brachysporum Rostrup. In Notes on diseases of trees in the southern Appalachians 1. Phytopathology 3: 133-139, figs. 5-10. 1913. Spaulding, P. The present status of the white-pine blights. U. S. Dept. Agr. Bur. Pl. Ind. Cire. 35: 1-12. 1909. PINE DISEASES PH Brown Fer.t-Biicut Caused by Neopeckia Coulteri (Peck) Sace. The brown felt-blight of pine is a common disease at altitudes from six to eleven thousand feet above sea level in northwestern United States. The leaves and twigs are covered and matted together by an abundant growth of brown mycelium. It is indistinguishable from the brown felt-blight of other species of conifers. The behavior of this disease is in every way parallel to the similar disease of spruce which is discussed on page 317. LeaFr-Cast AND WITCHES’-BROOM OF WESTERN YELLOW PINE Caused by Hypoderma deformans Weir This disease is destructive to western yellow pine in the Northwest and on the Pacific Coast. A similar disease on Jeffrey pine in California may be caused by the same fungus. The needles of western yellow pine of all ages are killed. Seed- lings and young trees may be destroyed outright. On older trees the needles of the season become infected, gradually turn yellow and brown and fall from the twigs. They may remain on the tree for cne cr more years, however, and this gives the appearance that the needles cf all ages are affected. The mycelium enters the young twigs. The affected twigs remain stunted and large brooms are formed. The brooms hang from the limb. The black fruiting-bodies of the fungus break through the epidermis of the leaves in the autumn. They are mature the following spring and may shed their spores throughout the summer. Further details concerning the leaf- cast diseases will be found on page 38. REFERENCE Weir, J. R. Hypoderma deformans, an undescribed needle fungus of the western yellow pine. Jour. Agr. Res. 6:277-288, pl. 32, figs. 1-4. 1916. DAD MANUAL OF TREE DISEASES Twic-BLIGcHT Caused by Cenangium ferruginosum Fries This disease is reported as common and destructive in Europe on Scotch, Austrian and white pines and on European silver fir. In this country very little mention of it has been made. It is reported on white pine in Ohio and the causal fungus has been found on long-leaf, western yellow and Monterey pine. On these latter trees the fungus was not shown to be parasitic. Mature trees are more often affected than younger ones and the disease is unknown on trees less than five years old. In Europe this disease is said to occur in epiphytotics which sweep over large forest areas. Symptoms. The terminal buds of affected twigs die in the spring. Later the older needles turn red and die from the base to the tip. The dead needles fall and leave the twigs bare. Small fruiting-bodies are formed on the dead twigs and branches. In wet weather the fruiting-bodies open and are cup- shaped, measuring about one-eighth of an inch across. During dry weather they close and are more or less globose. In this condition they are dusty brown or black but when they are open the inner surface of the cup is yellowish or dirty greenish yellow. Cause. This twig-blight of pine is supposed to be caused by the fungus Cenangium ferruginosum. Asci containing ascospores are borne on the yellowish inner surface of the fruiting-bodies. The ascospores are forcibly ejected and borne by the wind for long distances. Other types of fruiting-bodies, resembling those described above, are also formed which produce simple spores. These, however, are not known to play any important part in the life history of the fungus. There is some question whether this fungus is primarily responsible for this disease. PINE DISEASES 273 It seems more probable that winter-drying and other types of winter-injury may account for the injury and that the fungus is secondary and only semi-parasitic. Control. The only measure of control known is to prune off the dead twigs and burn these, together with all other brush and refuse from coniferous trees that may be in the vicinity. REFERENCES Fink, Bruce. Injury to Pinus strobus caused by Cenangium abietis. Phytopathology 1: 180-183, pl. 26. 1911. Schwarz, Frank. Die Erkrankung der Kiefern durch Cenangium Abietis, pp. 1-126, pls. 1-2. 1895. MIstTLETOE Burits AND WITCHES’-BROOMS Caused by Razoumofskya campylopoda (Knglem.) Piper, and R. ameri- cana (Nutt.) Kuntze Western yellow and lodge-pole pine are affected respectively by these two dwarf mistletoe parasites. In northwestern . United States much damage results from the diseased condition they cause. The general result of burl and witches’-broom formation is a reduction in foliage which causes slow growth and finally death when infection is heavy. Likewise, the dis- eased areas of bark offer ready places of entrance for insects and wood-rotting fungi. Trees of all ages are affected. ‘Trees with the lower branches or trunk affected early in life suffer more severely than those infected later. The brooming of the lower branches diverts a large part of the growth energy of the tree and the tops are dwarfed and die, causing stag-headed or spike-topped trees. Symptoms. The roots from the germinating mistletoe seeds enter the leafy twigs or through wounds in the bark of older branches. T 274 MANUAL OF TREE DISEASES Swellings of the limb are first formed and later many abnormal branches are sent out and ragged broom-like growths are pro- duced. Burls at the base of the branches and on the side of the trunk also develop where the roots of the parasite find a foothold. The mistletoe plant may die but the stimulus still continues to cause the abnormal growth. The brooms may become so heavy when burdened with ice and snow that the limb breaks. The needles of the old brooms are usually smaller and shorter-lived than on healthy branches. For a general discussion of the mistletoe diseases of trees, see page 54. REFERENCE Weir, J. R. Mistletoe injury to conifers in the northwest. U. S. Dept. Agr. Bul. 360: 1-38, pls. 1-4, figs. 1-27. 1916. Burister-Rust or FiveE-NEEDLE PINES Caused by Cronartium ribicola Fischer de Waldheim The fungus causing the blister-rust of five-needle pines is native in Europe. With the extensive use of the American white pine in western Europe for forest-planting, it became widely distributed on this tree and was soon recognized as an important enemy of the white pine. As early as 1890 and 1900, it was prevalent in all the countries of western and northern Europe and was known in Siberia and Japan. The fungus is supposed to have been originally confined to the Swiss stone pine of Europe, which is not very seriously affected by it. In Germany, France, England and other countries of western Europe the blister-rust soon became so prevalent and de- structive that the further use of the American white pine in reforestation was largely abandoned. Previous to this time large numbers of white pine were grown in the forest nurseries, and this disease was found to affect seriously a large percentage of the trees in some regions. PINE DISEASES 275 Even with these facts known, no definite action was taken in the United States to prevent the introduction of this fungus, and in 1906 it was first found at Geneva, New York. Later, in 1909, it was discovered in recently imported seedling stock in New York, Vermont, New Hampshire, Massachusetts, Connecticut, Pennsylvania, Indiana and Ohio. The demand for white pine nursery stock both for forest and ornamental plantings had far exceeded the amount produced in this country at that time, and several hundred thousand trees had been im- ported annually from Germany and France. It is, therefore, not surprising that numerous diseased pines were found in the different states where this stock was planted. Although at- tempts were made to eradicate the known diseased trees, the fungus is now generally prevalent in the New England states and New York and is known in restricted areas in Wisconsin and Minnesota. All pines which have their needles in fascicles of five are ex- pected to be susceptible. It is definitely known that the eastern white pine, western white pine and sugar pine are susceptible. As yet the fungus has not been found in western United States where the two important western species of this group grow. The damage that may result to the five- needle pines in the forest in this country cannot be prophesied at this time. Young trees and the younger branches of older trees are most seriously affected. In plantations of European stock in New York state not more than one per cent of the trees were ever found affected. However, in several places under actual forest conditions in northeastern United States where the fungus has existed unnoticed for many years, a much larger percentage of the stand is affected. The fungus causing white pine blister-rust requires the pres- ence of some species of gooseberry or currant for the comple- tion of its life history. The spores developed on the pines cannot infect other pines but must lodge on the leaves of cur- 276 MANUAL OF TREE DISEASES rant or gooseberry bushes in order to continue the cycle of de- velopment. Spores are then produced throughout the summer on these plants which cause the infection of other goose- Fic. 52. — Blister-rust on twig of white pine. berries and currants. In the autumn another type of spores (teliospores) is developed on the affected currants and gooseberries and from these are formed basidiospores which cause the infection of the young branches of five-needled pines. The distribution of this fungus on the pines, therefore, is dependent on the presence or absence of gooseberries and currants, and if present the amount of damage done is somewhat dependent on their abundance. Unfortunately sev- eral species of these plants occur as common weeds practically throughout the range of the five-needle pines in the United States. Symptoms. The young leaf-bearing twigs are in- fected and the mycelium grows in the bark and may extend into the larger branches and trunks. The affected bark is usually swollen, but the tissue remains normal and healthy in appearance for two or three years. In the second or third spring after infection occurs, the prominent fruiting-pustules of the fungus appear on the bark (Figs. 52 and 53). These blister-like pustules are irregularly hemispherical or elongate, one-eighth to one-half inch across and orange-colored. PINE DISEASES 7. The covering of the blisters breaks and a fine yellow powder of thousands of spores dusts out and is blown away by the wind. The blister stage on the pine is formed in early spring and by midsummer the white coverings of the blisters disap- pear and only rounded depres- sions remain in the bark to mark their location. The area of bark from which the blisters are pro- duced usually dies but the my- celium extends into the surround- ing healthy bark. The yellow blisters are produced year after year from the newly invaded bark until on older trees cankers several feet long are sometimes formed. Usually the branch or trunk is soon girdled and the parts of the tree beyond the girdled point die. The fungus cannot exist except in living tissue and, therefore, is not har- bored after the affected part of the tree is killed. Young trees with the trunk affected show a stunted and compact growth and a slight yellowish color instead of the normal green. Infected currant and goose- berry leaves show slightly yellow- ish spots which are more distinct on the under surface. Small yellowish blisters are pushed out é Fic. 53. — Blister-rust on trunk of from the lower epidermis and young white pine. 278 MANUAL OF TREE DISEASES when the covering is broken, a rounded mass of yellow spores (urediniospores) is exposed (Fig. 54). Later in the Fic. 54.— Cronartium ribicola (uredinial stage) on under side of currant leaf. season, from the same lesions several slender brown bristle- like structures are pushed out from the under sides of the leaves (Fig.55). When the affected areas of the leaf are numerous, these brown bristles so completely cover the under side of the leaf that it appears as coarse brown felt, and thus the common name for this disease on cur- rants and gooseberries is felt-rust. But little damage is caused to the affected bushes, al- though defoliation may occur earlier than nor- mally when the leaves are heavily infested. The species of currant Fic. 55.— Cronartium ribicola (telial stage) on under side of currant leaf. Felt-rust. and gooseberry vary PINE DISEASES 279 greatly in susceptibility. The cultivated black currant is most susceptible, the under sides of the leaves being often completely covered with the felt-stage. Gooseberries in general are more resistant than currants. Cause. The blister-rust of five-needle pines and the felt-rust of cur- rants and gooseberries are caused by the fungus, Cronartiwm ribicola. Before the stages on the two kinds of plants were known to be caused by the same fungus, the stage on the pine was called Peridermium strobi. The life history of this fungus has been indicated above. The eciospores formed in the blisters on the pine branches infect the leaves of gooseberry and currant. After a period of development in the leaf-tissue, urediniospores are formed which infect other gooseberry and currant leaves. From the same pustules the teliospores are developed in long hair-like masses. These spores are not disseminated but germinate and produce small, globose spores (basidiospores) on the short germ-tubes. The basidiospores are shot from their attachment and may cause infection of the pine. In this way, although the pine is not infected by the zeclospores produced in the blisters, the mycelium of the fungus after about two months’ growth in the currant or gooseberry produces the kind of spore which will infect the pines. Weather conditions in relation to the spread and severity of attack of this fungus are not fully understood. Moisture is necessary for the germination of the different spores and from analogy to other similar diseases, it would be expected that the stage on currants and gooseberries would be more abundant in wet seasons. The distance over which the spores are transported by the wind depends largely on prevailing air currents and the topography of the region. In a dense growth of underbrush in the forest the fungus would not be 280 MANUAL OF TREE DISEASES expected to spread as rapidly in a given season as it would in more open country. Control. Although repeated attempts had been made since 1896 to secure a federal law which would prevent the entry of foreign stock likely to harbor and introduce dangerous fungi and in- sects, such a law was not enacted until 1912. The blister-rust fungus had by that time become established in various locali- ties in northeastern United States. The extermination of the fungus was attempted where it was known. In New York all the known areas where foreign white pine stock was planted were inspected yearly. The diseased trees and all currant and gooseberry bushes within five hundred feet of them were destroyed. When the fungus was found prevalent in western Massachusetts in the fall of 1915, more extensive surveys were planned for 1916 and as the result, the fungus was found to be generally prevalent throughout the territory east of the Hudson River and Lake Champlain. In 1917 it was found practically throughout New York state. Despite the previous attempts at its eradication in isolated areas and any efforts that may be made at general control in the future, the fungus is now so well established in this country that it will continue to spread and exist wherever conditions are favorable. In certain regions in which the white and other five-needle pines are important as ornamentals, the native wild species of gooseberry and currant are very scarce. Such conditions exist in the lower Hudson River valley and on Long Island. In these regions this disease could easily be controlled if the cultivated garden varieties of gooseberry and currant were eliminated. However, when one neighbor grows one of these plants and the next has five-needle pines to protect, no generally satisfactory agreement will be reached in most cases. ‘The elimination of currants and gooseberries for a distance of one- PINE DISEASES Sil half mile from the pines will probably control this rust. If this distance is not possible, a separation of five hundred feet or more will be partially beneficial. In forested areas where wild currants and gooseberries are common, the further growing of white pine may have to be abandoned. The elimination of the bushes over extensive areas will probably never prove as profitable as planting or encouraging natural reproduction of some other species of tree suited to the conditions. Where currants and gooseberries are not very abundant and the experiment of eliminating them is thought practicable, results may be obtained if the work is vigorously prosecuted year after year. The total cost and the possibilities of failure must influence the planning of this kind of control when timber values alone are to be considered. REFERENCES Spaulding, P. The blister rust of white pine. U. S. Dept. Agr. Bur. Pl. Ind. Bul. 206: 1-88, pls. 1-2, figs. 1-5. 1911. (Bibli- ography given.) Spaulding, P. The white-pine blister rust. U.S. Dept. Agr. Farmers’ Bul. 742: 1-15, pl. 1, figs. 1-5. 1916. Spaulding, P. New facts concerning the white-pine blister rust. U. S. Dept. Agr. Bul. 116: 1-8. 1914. Spaulding, P. Foresters have a vital interest in the white-pine blister rust. Proc. Soe. Am. For. 11: 40-47. 1916. Atwood, G. G. Emergency bulletin on the blister rust of pines and the European currant rust. New York Dept. Agr. Hort. Bul. 2: 1-15, pls. 1-2. 1909. Paul, B. H. The pine blister. New York Conservation Com. Bul. 15: 1-18, figs. 1-8, map. 1. 1916. SWEET-FERN Rust Caused by Cronartium comptonie Arthur This rust disease occurs on two- and three-needle pines in eastern United States and is commonly known as blister-rust. It is found on the native pitch, scrub, loblolly, western yellow, 282 MANUAL OF TREE DISEASES jack, lodge-pole, Jeffrey, Norway and short-leaf pines and on the imported Scotch, Austrian and mugho pines. Only very young trees are generally affected and it is most important as a nursery and young plantation disease. It is known to have caused the death of a large number of the susceptible pines in certain nurseries in Massachusetts, Connecticut, New York and Michigan. The common weeds, sweet-fern (Comptonia asplenifolia) or sweet-gale (Myrica Gale) must be in the vicinity of the pines for this fungus to complete its life history. If this plant is not present, the unaffected trees will not be en- dangered by the diseased pines. Symptoms. This rust produces symptoms on two- and _ three-needle pines very similar to the blister-rust which occurs on five- needle pines (see page 276). Small branches and the trunks of young trees are affected. Slight enlargements are usually formed. On these swollen areas yellowish blisters are pushed out in early spring. The arched covering breaks and the orange-colored spore-mass inside dusts out as a fine powder and is blown away. On the sweet-fern and sweet-gale (Comptonia asplenifolia and Myrica Gale), small yellowish pustules are formed on the under sides of the leaves in summer, followed later by brown bristles which project from the same spots. These structures are similar to those formed on gooseberry and currant leaves affected with felt-rust (see page 277). Cause. The sweet-fern rust of two- and three-needle pines is caused by the fungus Cronartium comptonie (=Peridermium comp- tonie Orton and Adams), a close relative of the blister-rust fungus on white pine. The life history and control of this rust-fungus is similar to the white pine blister-rust except that it has PINE DISEASES 283 its alternate stages on sweet-fern and sweet-gale instead of on currants and gooseberries (see page 279). REFERENCES Spaulding, P. Notes on Cronartium Comptonie, II. Phytopathol- ogy 3:308-310. 1913. Clinton, G. P. Cronartium Comptoniew Arth. (I. Peridermium pyri- forme Pk.). Connecticut Agr. Exp. Sta. Ann. Rept. 1907— 1908 : 380-383, pl. 28. 1908. Weir, J. R. Observations on the pathology of the jack pine. U.S. Dept. Agr. Bul. 212: 1-10, pl. 1, figs. 1-4. 1915. Spaulding, P. Noteson Cronartium Comptonie III. Phytopathology 7:49-51. 1917. CoMANDRA Rust Caused by Cronartium comandre Peck This is one of the six blister-rust diseases of the stems of pines in the United States. Although known commonly as blister-rust, it is here called the Comandra rust of pines to distinguish it from the other five similar diseases. The Co- mandra rust occurs on pines having two or two to three needles in a bundle and not on the three-needle pitch pines. It has been found on lodge-pole, jack, western yellow and table-moun- tain pine, in several eastern, north-central and western states. A part of the life history of the causal fungus is spent on species of Comandra and on these plants it has been found over the entire northern and central part of the United States from the Atlantic to the Pacific. In the western states the Comandra rust is an Important disease of the pines which are susceptible. In certain regions a large percentage of the younger trees has been found affected or killed. Older trees are rarely attacked. In Pennsylvania the disease causes the death of many young table-mountain pines. Symptoms. The trunks and limbs of trees less than two or three inches in diameter are attacked. Spindle-shaped swellings are pro- 284 MANUAL OF TREE DISEASES duced which may be several inches long except in very young trees where no swellings are noticeable. The trunk may become infected by the fungus extending into it from infected branches. The fruiting-bodies appear on the affected bark in early spring. They are yellowish blisters, usually about a quarter of an inch or smaller in diameter and may be longer than broad. The covering of the blister breaks and the spores are blown away as a fine orange-colored powder. The spores from the yellow blisters infect the leaves and younger stems of species of Comandra. Small yellowish or reddish pustules are formed on light colored areas of the leaf and a little later brown bristles project from the same spots. The plants are dwarfed and often premature defoliation occurs when the leaves are badly affected. Cause. The Comandra rust of pines is caused by the fungus Cronar- tium comandre (=Peridermium pyriforme Peck). The ecio- spores formed in the blisters on the pine bark cause the infection of the leaves and young stems of Comandra. On that host urediniospores are formed which infect other Comandra plants. The urediniospores are closely followed by the production of the bristle-like teliospore columns, the individual cells of which germinate and produce the basidiospores. ‘These latter spores are wind-borne and may cause the infection of the pines, if they are near by. Both the pines and species of Comandra must be present in the same locality for this fungus to exist on the pines. Control. The elimination of the species of Comandra from the vicinity of nurseries and young plantations is necessary if this disease is to be controlled. In the forest the diseased trees may be destroyed as a measure of protection for the young growth PINE DISEASES 285 coming on. However, a few will always escape detection and if the Comandra plants are abundant, several pines may be- come infected during a season when only one existed in the spring. REFERENCES Arthur, J. C., and Kern, F. D. The rediscovery of Peridermium pyri- forme Peck. Science 38: 311-312. 1913. Hedgecock, G. G., and Long, W. H. A disease of pines caused by Cro- nartium pyriforme. U.S. Dept. Agr. Bul. 247: 1-20, pls. 1-2, fe. Ie 1915: Hedgeock, G. G., and Long, W. H. Two new hosts for Peridermium pyriforme. Jour. Agr. Res. 5: 289-290, pl. 27. 1915. Orton, C. R.,and Adams, J. F. Notes on Peridermium from Pennsyl- vania. Phytopathology 4: 23-26, pl. 3. 1914. CasTILLEJA Rust Caused by Cronartium coleosporioides (D. and H.) Arthur This blister-rust disease occurs from the Rocky Mountains to the Pacific Coast Range and from Canada to Mexico. It is exceedingly destructive to lodge-pole and western yellow pine. Large knots and cankers are formed on lodge-pole pine which at times are similar to the oak rust of pines (see page 287). The trunks of many trees five inches in diameter are girdled by the cankers, which may be from two to eight feet long. The bark soon dies and the death of the tree or branch follows. Fifty per cent of the stand is sometimes seriously affected. This fungus requires the presence of the weeds, Castilleja miniata and other species of the same genus, in the vicinity of the pine in order to complete its development. When these plants do not exist, this fungus cannot affect the pines. Symptoms. Both young and old trees are affected. Small trees in the nursery show but little enlargement of the affected branches or trunk. Large orange-colored blisters burst through the 286 MANUAL OF TREE DISEASES bark, and the spores within are shed as a fine powder. The affected limbs of older trees may show but little swelling or, as in the case of lodge-pole pine, large knots or galls and cankers are produced (Fig. 56). After the first crop of blisters is formed, the bark usually dies and the mycelium extends its activities to the healthy bark around the dead area. This process of en- largement of the canker or gall con- tinues until the limb or trunk is girdled and death results. On the under sides of the leaves of species of Castilleja, small yellowish spots appear during the summer. Later numerous brownish bristles are pushed out from these spots. The appearance of the leaf is very similar to currant and gooseberry leaves af- fected with felt-rust (see page 277). Cause. The blister-rust which affects west- ern pines and species of Castilleja is caused by the rust-fungus Cronartium coleosporioides (= Peridermium filamen- tosum, the Rocky Mountain form of Peridermium Harknessii). The life history of this rust is similar to that Fig. 56.—Blister-rust or of Cronartiwm ribicola described on are rust on lodge-pole page 279. The eciospores germinate and infect the Castilleja leaves. Ure- diniospores propagate the fungus on this host throughout the summer and the teliospores and basidiospores are formed in late summer. Infection of the pine takes place in the autumn. PINE DISEASES 287 Control. In the western forests, the grazing animals keep the Castilleja plants down to a minimum. Where grazing is not common, these plants grow in large numbers and predispose the pines to infection. All Castilleja plants should be eradicated for a distance of a half mile around nurseries in which the species susceptible to this rust-fungus are grown. REFERENCES Weir, J. R., and Hubert, E. E. A rs s) ‘i rt 7 ~ = ae ‘- ve ’ APPENDIX ComMMON NAMES OF TREES A usr of the common names of trees used in this manual is given below with the scientific name opposite cach. In most cases, the common name recommended by Sudworth * is adopted. Alder (general) Alpine fir Alpine lareh Arbor-vite (general) Arbor-vite (specific) Ash (general) Aspen Bald cypress Balm of Gilead Balsam fir Basswood (general) Basswood (specific) Beech Birch (general) Black ash Black gum Black jack oak Black poplar Black spruce Black walnut Box-elder Buckeye (general) Bur oak Butternut California buckeye Carolina hemlock Alnus sp. Abies lasiocarpa Nutt. Larix Lyallii Parl. Thuja sp. Thuja occidentalis Linn. Fraxinus sp. Populus tremuloides Michx. Taxodium distichum Rich. Populus balsamifera Linn. Abies balsamea Mill. Tilia sp. Tilia americana Linn. Fagus grandifolia Ehbrh. Betula sp. Frazxinus nigra Marsh. Nyssa sylvatica Marsh. - Quercus marilandica Muench. Populus nigra Linn. Picea mariana B.S. P. Juglans nigra Linn. Acer Negundo Linn. Aisculus sp. Quercus macrocarpa Michx. Juglans cinerea Linn. Aisculus californica Nutt. Tsuga caroliniana Engelm. 1Sudworth, G. B. Check list of the forest trees of the United States, their names and ranges. U.S. Dept. Agr. Div. Forestry Bul. 17: 1-144. 1898. 361 362 Catalpa (general) Cedar (general) Chestnut Chestnut oak Chinquapin ° Colorado blue spruce Cottonwood Coulter pine Cuban pine Dogwood Douglas fir Dwarf juniper Eastern hemlock Eastern larch Elm (general) Engelmann spruce Kuropean chestnut Fir (general) Fraser fir Grand fir Gray pine Green ash Hackberry (general) Hardy ecatalpa Haw (general) Hemlock (general) Hickory (general) Horse-chestnut Incense cedar Jack pine Japanese chestnut Jeffrey pine Juniper (general) Knob-cone pine Larch (general) Large-tooth aspen Limber pine Loblolly pine Locust (general) Locust (specific) Lodge-pole pine Lombardy poplar Long-leaf pine Maple (general) APPENDIX Catalpa sp. Chamecyparis sp. and Libocedrus sp. Castanea dentata Borkh. Quercus Prinus Linn. Castanea pumila Linn. Picea Parryana Parry Populus deltoides Marsh. Pinus Coulteri Lamb Pinus heterophylla Sudw. Cornus florida Linn. Pseudotsuga taxifolia Brit. Juniperus communis Linn. Tsuga canadensis Carr. Larix laricina (Du Roi) Koch. Ulmus sp. Picea Engelmanni Engel. Castanea sativa Mill. Abies sp. and Pseudotsuga sp. Abies Fraseri Poir. Abies grandis Lindl. Pinus Sabiniana Dougl. Fraxinus lanceolata Borkh. Celtis sp. Catalpa speciosa Warder Crategus sp. Tsuga sp. Carya or Hicoria sp. Aisculus Hippocastanum Linn. Libocedrus decurrens Torr. Pinus Banksiana Lamb. Castanea crenata Sieb. and Zuce. Pinus Jeffreyt Juniperus sp. Pinus attenuata Lemmon Larix sp. Populus grandidentata Michx. Pinus flexilis James Pinus Teda Linn. Robinia sp. Robinia Pseudacacia Linn. Pinus contorta Loud. Populus nigra italica Du Roi Pinus palustris Mill. Acer sp. Monterey pine Mountain ash (general) Mountain juniper Noble fir Norway pine Norway spruce Nut pine Oak (general) Ohio buckeye One-seed juniper Paper bireh Pine (general) Pitch pine Pond pine Poplar (general) Red ash Red juniper Red maple Red oak Red spruce River birch Rocky Mountain juniper Sand pine Searlet oak Seotch pine Serub pine Service-berry (general) Shasta red fir Short-leaf pine Silver maple Single-leaf pine Sitka spruce Spruce (general) Spruce pine Striped maple Sugar pine Swiss stone pine Sycamore Table-mountain pine Utah juniper Western chinquapin Western hemlock Western larch Western white pine Western yellow pine APPENDIX 363 Pinus radiata Don. Sorbus sp. Juniperus sabinoides Sarg. Abies nobilis Lindl. Pinus resinosa Ait. Picea excelsa Link Pinus edulis Engelm. Quercus sp. Aisculus glabra Willd. Juniperus monosperma Sarg. Betula papyrifera Marsh. Pinus sp. Pinus rigida Mill Pinus serotina Michx. Populus sp. Fraxinus pennsylvanica Marsh. Juniperus virginiana Linn. Acer rubrum Linn. Quercus rubra Linn. Picea rubra Dietr. Betula nigra Linn. Juniperus scopulorum Sargent Pinus clausa Sarg. Quercus coccinea Muench. Pinus sylvestris Linn. Pinus virginiana Mill. Amelanchier sp. Abies magnifica Murr. Pinus echinata Mill. Acer saccharinum Linn. Pinus monophylla Torr. and Frem. Picea sitchensis T. and M. Picea sp. Pinus glabra Walt. Acer pennsylvanicum Linn. Pinus Lambertiana Doug}. Pinus Cembra Linn. Platanus occidentalis Linn. Pinus pungens Lamb. Juniperus utahensis Lemm. Castanopsis chrysophylla de C. Tsuga heterophylla Sarg. Larix occidentalis Nutt. Pinus monticola Dougl. Pinus ponderosa Laws. 364 White ash White birch White cedar White elm White fir White oak White pine White spruce Yellow birch Yellow buckeye Yellow cedar Yellow oak Yellow poplar APPENDIX Fraxinus americana Linn. Betula populifolia Marsh. Chamecyparis thyoides B. 8. P. Ulmus americana Linn. Abies concolor Parry Quercus alba Linn. Pinus Strobus Linn. Picea canadensis B. S. P. Betula lutea Michx. f. Zisculus octandra Marsh. Chamecyparis nootkatensis Spach. Quercus velutina Lam. Liriodendron Tulipifera Linn. SYNONYMY OF POoLYPORE NAMES Following is a list of the polypore names used in this manual. Opposite each is the name applied to the same fungus by Murrill’ in the North American Flora. Fomes annosus Fries Fomes applanatus Fries Fomes Earlet (Murr.) Sace. Fomes Everhartii (Ellis and Gall.) Schrenk Fomes fomentarius Fries Fomes fraxinophilus Peek Fomes fulvus Fries Fomes geotropus Cooke Fomes igniarius Fries Fomes juniperinus Schrenk Fomes officinalis Fries Fomes pinicola Fries Fomes rimosus Berkeley Fomes roseus Fries Fomes texanus (Murr.) Hedg. and Long Polyporus amarus Hedgeock 1Murrill, W. A., North American Flora, 9: 1-131. Fomes annosus (Fries) Cooke Elfvingia megaloma (Lev.) Murr. Pyropolyporus Earlet Murr. Pyropolyporus Everhartii (Ell. and Gall.) Murr. Elfvingia fomentaria (L.) Murr. Fomes fraxinophilus (Peck) Sace. Pyropolyporus fulvus (Seop.) urr. Pyropolyporus igniarius (L.) Murr. Pyropolyporus juniperinus (Schrenk) Murr. Fomes laricis (Jaeq.) Murr. Fomes ungulatus (Schaeff.) Saee. Pyropolyporus Robinie Murr. Fomes roseus (Alb. and Sehw.) Cooke Pyropolyporus tecanus Murr. 1907. APPENDIX 365 Polyporus Berkeleyi Fries Grifola Berkeleyi (Fries) Murr. Polyporus borealis Fries Spongipellis borealis (Fries) Pat. Polyporus betulinus Fries Piptoporus suberosus (L.) Murr. Polyporus croceus Fries Aurantiporus Pilote (Schw.) Murr. Polyporus dryadeus Fries Tonotus dryadeus (Fr.) Murr. Polyporus Ellisianus (Murr.) Long Tryomyces Ellisianus Murr. Polyporus frondosus Fries Grifola frondosa (Dicks.) S. F. Gray Polyporus obtusus Berkeley Spongipellis unicolor (Schw.) Murr. Polyporus Rheades Fries Tonotus dryophilus (Berk.) Murr. Polyporus Schweinttzii Fries Pheolus sistotremoides (Alb. and Schw.) Murr. Polyporus squamosus Fries Polyporus caudicinus (Secop.) Murr. Polyporus sulphureus Fries Letiporus speciosus (Batarr.) Murr. Trametes pint Fries Porodedalia pint (Thore) Murr. Trametes suaveolens Fries Trametes suaveolens Fries GLOSSARY Acervulus (acervuli). Open, saucer-shaped, asexual fruiting-body. fEciospore. One of the types of spores formed by the rust-fungi. AXfciospores are produced in the blisters on conifers in the case of the blister-rusts. The juniper and cedar rust-fungi form zeciospores on the pomaceous host. Ascospore. Sexually formed spores which are borne within a sac ealled an ascus. The asci are in turn borne on or in various types of fruiting-bodies. Ascus (asci). Sac-like structures containing ascospores. Asci are borne in open or closed fruiting-bodies. Perithecia contain asci. Bacterium (bacteria). Small, microscopic plants. Plants consist of single cells, which may be motile. Parasitic forms cause in- fectious diseases of plants and animals. Basidiospore. Short lived spores borne on germ-tubes of teliospores in the rust-fungi. They are forcibly discharged and are carried by the wind. Cambium. Region of growth in a woody stem or root, at which wood is formed on the inside and bark on the outside. Canker. A dead area of bark. Chlorophyl. The green coloring material produced in the leaves of the higher plants. Chlorophyl is instrumental in making starch from carbon dioxide gas and water. 366 APPENDIX Enzyme. A complex chemical compound capable of causing the transformation of certain organic substances into substances of greater or less complexity without itself entering into the product. Epiphytotic. A plant disease which assumes an unusual and generally destructive nature in a locality. Usually called an epidemic, which term refers only to human diseases. Fruiting-body. Large or small, open or closed structures made of ° mycelium in which the spores of fungi are formed. Fungus. Simple plants lacking chlorophyl. Consisting of mycelium which may be massed to form large fruiting-bodies. Fungi obtain food by decomposing living or dead plant and animal tissue. Fusiform. Spindle-shaped. Germ-tube. A short tube which grows from a viable spore. The germ-tube then branches and a new mycelium is formed if growth- conditions are suitable. Gill. The pendent plates or lamella found on the under side of toadstools. The spores of the fungus are borne on the sides of the gills. Haustorium (haustoria). Special branch of the mycelium which is pushed into a cell to obtain food-materials. Heartwood. The wood at the center of a tree, which contains no living cells and serves only for support. Heterecious. Said of a parasitic fungus which requires more than one kind of host for the completion of its life history. Host. Any plant in which a parasite grows. Hypertrophy. Enlargement of a portion of a plant, as galls on limbs. Hypha (hyphex). Individual branches of the mycelium of a fungus. Infect. Said of a parasitic organism when it succeeds in establish- ing parasitic relations with a host-plant. Infection. The act of infecting, see above. Infection court. Any place or area of a host-plant where infection occurs. Also said of any place where infection is possible. Lesion. Any definitely diseased area in which the primary cause of the disease is present. Mycelium (mycelia). The vegetative body of a fungus, made up of long threads containing protoplasm. Parasite. An organism which lives in or on another living organism for the purpose of obtaining food-materials. Parenchymatous. Tissue composed of thin walled cells which are capable of further differentiation. Pathogene. Any factor which causes disease, usually restricted to living organisms which live parasitically. Perithecium (perithecia). A closed globose or flask-shaped fruiting- body containing asci and ascospores. Spores usually forcibly discharged. APPENDIX 367 Protoplasm. Living substance within the cells of plants and animals. The seat of growth and many other functions which are charac- teristic of living things. Pycnidium (pyenidia). An ineclosed globose or flask-shaped fruit- ing-body containing simple asexual spores. Rhizomorph. A compact bundle of mycelium arranged parallel to form a root-like structure. See shoe-string root-rot, page 78. Saprophyte. A living organism which obtains its food-materials from dead organic material. See Parasite. Sapwood. The wood between the heartwood and bark. Sapwood contains living cells and is the tissue which is active in translo- eating food-materials to all parts of the tree. Sclerotium (sclerotia). A compact, more or less globose structure made of closely aggregated mycelium. Usually a resting body rich in stored food. Spore. A portion of the mycelium which is detached and serves as a propagative or reproductive body, corresponding to the seeds of higher plants. Spores may be formed sexually or asexually. Stomate. Specialized structures with an opening in the center, found on the surface of leaves. Stomates open and close and regulate the exchange of gases and water vapor between the interior of the leaf and the surrounding atmosphere. Stroma (stromata). Compact aggregation of mycelium forming a fungous layer. Fruiting-bodies may be formed imbedded in the stroma. Teliospore. A type of spore formed by the rust-fungi. All rust- fungi form teliospores and basidiospores. They may omit any one or all of the other stages. Teliospores in many species over- winter. When they germinate they form basidiospores directly. Urediniospore. A type of spore formed by the rust-fungi. These spores are produced in summer and serve to distribute the fungus rapidly during the growing season. Urediniospores are usually produced from mycelium that originated from sciospore infec- tion. Later teliospores are formed from the same mycelium. GENERAL BIBLIOGRAPHY OF TREE DISEASES AMERICAN PUBLICATIONS Atkinson, G. F. Studies of some shade tree and timber destroying fungi. Cornell Univ. Agr. Exp. Sta. Bul. 193: 199-235, figs. 56-94. 1901. Cook, M. T. Diseases of shade and forest trees. Jn The planting and care of shade trees. Forest Park Reservation Commission of New Jersey, pp. 93-124, figs. 36-43. 1912. 368 APPENDIX Cook, M. T. The diseases of tropical plants, pp. 1-317, figs. 1-85. 1913. Duggar, B. M. Fungous diseases of plants, pp. 1-508, figs. 1-240. 1909. Freeman, EK. M. Minnesota plant diseases, pp. 1-482, figs. 1-211. 1905. Galloway, B. T., and Woods, A. F. Diseases of shade and ornamental trees. U.S. Dept. Agr. Yearbook 1896: 237-254, figs. 53-57. 1897. Harshberger, J. W.