nes ta ttanntae Sth alaag *) ns peeves red Fearne ——~ + : > eg eS - ——wr ae a pa ag — . ae ae . Sere : OS ne “ a en NAL Un —‘E tt 3 Sirf SURVEY Ay ‘i He ‘yan ie oe . ATG iy if Aerie P ai ¥ Digitized by the Internet Archive in 2010 with funding from University of Illinois Urbana-Champaign http://www.archive.org/details/illinoistreesthe461961 cart Bo. 26 °F ILLINOIS TREES: THEIR Diseases J. CEDRIC CARTER | DELI MOLS NATURAL HISTORY SURVEY | Cirewlar 46 { Second Printing, | With Alterations THE LIBRARY OF THE ann | MAY 22 1961 NATURAL iS ee HISTORY SURVEY iuERSiTY OF ALLINIHE MAY 12 1961 LIBRARY Ui : SeRPAg eh © be al deb leNtOules OTTO KERNER, Governor DEPARTMENT OF REGISTRATION AND EDUCATION WILLIAM SYLVESTER WHITE, Director fennel: HISTORY SURVEY DIVISION HARLOW B. MILLS, Chief ILLINOIS TREES: THEIR Diseases J. CEDRIC CARTER Circular 46 Second Printing, With Alterations PeetNMOLS NATURAL HISTORY SURVEY Printed by Authority of fs the State of Illinois \\i April, 1961 STATE sOF ALL ENOwS Orro Kerner, Governor BOARD OF NATURAL RESOURCES AND CONSERVATION Wituam Syivester Wuire, Chairman; A. E. Emerson, Ph.D., Biology; Wautrer H. Newuouse, Ph.D., Geola Rocer Apams, Ph.D., D.Sc., Chemistry; Roperr H. Anverson, B.S.C.E., Engineering; W. L. Everitt, E.E., Phi Representing the President of the University of Illinois; Detyte W. Morris, Ph.D., University NATURAL HISTORY SURVEY DIVISION, Urbana, Illinois SCIENTIFIC AND TECHNICAL STAFF Hartow B. Mius, Ph.D., Chief Bessie B. East, M.S., Assistant to the Chief Section of Economic Entomology Grorce C. Decxer, Ph.D., Principal Scientist and Head J. H. Biccer, M.S., Entomologist L. L. Eneuisu, Ph.D., Entomologist W. H. Lucxmann, Ph.D., Entomologist Wituis N. Bruce, Ph.D., Entomologist ; Joun P. Kramer, Ph.D., Associate Entomologist Ronatp H. Meyer, M.S., Assistant Entomologist Ricuarp J. Dysart, B.S., Assistant Entomologist Roy E. McLaucuuin, B.S., Technical Assistant Recrxatp Roserts, M.S., Technical Assistant James W. Sanrorp, B.S., Technical Assistant EarL STADELBACHER, B.S., Technical Assistant Wittiam C. Moye, M.S., Technical Assistant Sue E. Watkins, Technical Assistant H. B. Perry, Ph.D., Extension Specialist in Entomology* Stevenson Moore, III, Ph.D., Extension Specialist in Entomology* : Zenas B. Noon, JIr., M.S., Research Assistant* Crarence E. Wuire, B.S., Instructor in Entomology Extension* Costas Kousxo.exas, M.S., Research Assistant* Ama. CHanpra BanerjEE, M.S., Research Assistant* Vicror T. Wiriiams, B.S., Research Assistant* Section of Faunistic Surveys and Insect Identification H. H. Ross, Ph.D., Systematic Entomologist and Head Mitton W. Sanverson, Ph.D., Taxonomist Lewis J. Stannarv, Jr., Ph.D., Taxonomist | Puuie W. Situ, Ph.D., Associate Taxonomist Leonora K. Groypv, MS., Assistant Taxonomist H. B. Cunnincuam, M.S., Assistant Taxonomist Ruru P. Casu, Technical Assistant Joun M. Kincsorver, MS., Research Assistant Epwarp O. Mout, Research Assistant Joun D. Unzicxer, Research Assistant Taraat K. Mitr, M.S., Research Assistant* Section of Aquatic Biology Georce W. Bennett, Ph.D., Aquatic Biologist and Head Wicuiam C. Starrett, Ph.D., Aquatic Biologist R. W. Larimore, Ph.D., Aquatic Biologist Davi H. Buck, Ph.D., Associate Aquatic Biologist Ropert C. Hirtipran. Ph.D., Associate Biochemist Donatp F. Hansen, Ph.D., Associate Aquatic Biologist Wituiam F. Cuivpers, M.S., Assistant Aquatic Biologist Marirran Martin, Technical Assistant Ropert TD. Crompton, Field Assistant Rotirs D. Anpvrews, III, B.S., Field Assistant Larry S. Goopwix, Laboratory Assistant Arnotp W. Fritz, B.S., Field Assistant* CONSULTANTS: Herreto.tocy, Hopart M. Smiru, Ph.D., Norman D. Levine, Ph.D., Professor of Veterinary Parasitology and of Veterinary Research, University of Illn Witpiire RESEARCH, Wittarv D. Kurmstra, Ph.D., Professor of Zoology and Durector of Co-operative Wil Research, Southern Illinois University. *Employed on co-operative projects with one of several agencies: University of Illinois, Illinois Agricul) Extension Service, Illinois Department of Conservation, National Science Foundation, United States Departme Agriculture, United States Fish and Wildlife Service, United States Public Health Service, This paper is a contribution from the Section of Applied Botany and Plant Pathology. (30235—4M—1-61) DEPARTMENT OF REGISTRATION AND EDUCATI Wiriram Sytvester Waite, Dire President of Southern Illi Section of Aquatic Biology—continued Davin J. McGinty, Field Assistant* Cuarces F. Tuoits, III, A.B., Field Assistant™ Section of Applied Botany and Plant Pathology J. Cepric Carter, Ph.D., Plant Pathologist and Hea J. L. Forsserc, Ph.D., Plant Pathologist G. H. Boewe, M.S., Associate Plant Pathologist 1 Ropert A. Evers, Ph.D., Associate Botanist Rosert Dan NeeExy, Ph.D., Associate Plant Patholq E. B. Himenicx, Ph.D., Associate Plant Pathologist Water Harrstirn, Ph.D., Assistant Plant Pathologi, D. F. Scuoreneweiss, Ph.D., Assistant Plant Patholq Heritey C. Tuompson, B.S., Research Assistant ! Anne Roprnson, M.A., Technical Assistant Section of Wildlife Research : Tuomas G. Scort, Ph.D., Game Specialist and Hed Ratew E. Yearrer, Ph.D., Game Specialist i F. C. Beurrose, B.S., Game Specialist H. C. Hanson, Ph.D., Associate Game Specialist , Ricuarp R. Graser, Ph.D., Associate Wildlife Speci Ronatp F. Lasisxy, M.S., Associate Wildlife Speci Guren C. Sanperson, M.A., Associate Wildlife Speci Maryorie J. Scuiatrer, Technical Assistant D. G. Rose, B.S., Technical Assistant Howarp Crum, Jr., Field Assistant Rexrorp D. Lorv, D.Sc., Project Leader* Jacx A. Exxis, M.S., Project Leader* Ropert I. Smiru, M.S., Progect Leader* Bossie Joe Verts, M.S., Project Leader* Rateuw J. Exxuis, M.S., Project Leader* j Wiriiam L. Anperson, B.S., Assistant Project Led James A. Harper, M.S., Assistant Project Leader*® } Davin A. CastTEEL, B.S., Assistant Project Leader*™ P. J. Rao, B.V.Sc., M.A., Research Assistant* Ann C. V. Haumes, B.S., Research Assistant* T. U. Meyers, Research Assistant* Erwin W. Pearson, M.S., Field Mammalogist* Ricuarp D. Anprews, M.S., Field Mammalogist* Keito P. Daururin, Assistant Laboratory Attendant* mm ann inn Section of Publications and Public Relations James S. Ayars, B.S., Technical Editor and Head BiancHe P. Youne, B.A., Assistant Technical Fidit Epwaxp C. Visnow, M.A., Assistant Technical Edit Wiruram E. Crark, Assistant Technical Photographe Technical Library Rutm Ro WaARRIcK, Biss) Bussleoe Nett Mies. M.S., B.S.L.S. Librarian ‘ Technical Librar . Assistant Technical Professor of Zoology, University of Illinois; ParastToL and others. GON GEN TS What Produces Tree Diseases?... 1 Cherry—Rust, Brown Rot, Twig Infectious Agents—Fungi, Bac- Canker™ . 5.22... RANT ap-3 aed 43 teria, Viruses, Mistletoes 1 Chestnut—Chestnut Blight, Noninfectious Agents—Physio- Other"Cankers'..........0.0.05 45 logical Disturbances, Weath- Crab Apple—Scab, Rust, Fire er or Climatic Troubles, - : Pa: i lighten. oe cath. a ha 46 Chemical Injuries, Mechani- ats mea: Elm—Wetwood, Verticillium CaleingUriese. so... . 4 i : Z : : 3 Wilt, Dothiorella Wilt, Dutch Types of Tree Diseases wae Elm Disease, Phloem Necrosis 48 Leaf Diseases—Powdery Mil- i ; dew, Leaf Spot, Scorch, Chlo- Hackberry—Witches’-Broom 70 rosis, Chemical Injury 8 Hawthorn—Rust, Fire Blight... 71 Stem Diseases—Canker, Gall, Juniper—Cedar-Apple Rust, Ce- Dieback, Witches’-Broom, dar-Hawthorn Rust, Cedar- WUGOGEOGa ee ii 5 ass 0s spel Et Quince Rust, Juniper Blight... .71 Bee Diseases oe Linden—Verticillium Wilt....... 75 : oot on : of Maple—Anthracnose, Tar Spot, Diagnosis of Tree Diseases eB Scorch, Canker and Dieback, fools and Their Uses........... 24 \Wermseilbhonen Wyville 5 o6sses5+550- ie) Tree Therapy............... 26 Mountain Ash—Fire Blight... .78 onay, Bees OPEC aa Oak—Anthracnose, Leaf Blister, fate and Hydrated Lime, Cy- : Rit : Rust, Smooth Patch, Dothio- cloheximide, DDT, Dichlone, : ; rella Canker, Oak Wilt, Shoe- Dodine, Ferbam, Methoxy- : - : string Root Rot 2 chlor, Organic Mercury, Sul- ; : fur, Thiram, Zineb, Ziram.. 27 Pine—Needle Blight, Needle Cast, Feeding—Deciduous Trees, Ev- Meelis JUSS SOK Mold: Waite me A Pine Blister Rust, Diplodia Tip ergreens, Liquid Feeding 31 Blight 36 Watering 85 PS eee ae et eded Pruning _ 35, Poplar—Rust, Cytospora Canker, Sanitation iP. 36 Dothichiza Canker, Crown Gall.90 Wound Treatment 37 Redbud—Canker, Verticillium Resistance and Immunity 38 WiC eter ote el i, ae ok 92 Arbor-Vitae—Winter Drying... 39 Spruce—Cytospora Canker, Ash—Anthracnose, Scorch, Rust, Diplodia ips Blight, .-5.-.. 4: 93 Cankers, White Mottled Rot....40 Syeamore—Anthracnose, Canker Bizch—Cankers 41 Stain ES . 95 Buckeye and Horsechestnut— Willow—Tar Spot, Leaf Rust, Leaf Bletch, Seorch 42 Cytospora Canker. Crown Gall 98 Catalpa—Verticillium Wilt 43 Trees Relatively Free of Disease 99 The photographs reproduced in this circular were taken by the follow- ing persons: J. Cedric Carter, William E. Clark, Ray R. Hamm, Robert E. Hesselschwerdt. and Charles L. Scott. The drawings were made by Robert E. Teegardin. The cover photograph, by Dr. Carter, shows the first tree affected with Dutch elm disease found in Illinois. Shoestring root rot frequently is found affecting the roots of oak trees that show staghead. ILLINOIS TREES: THEIR Diseases J. CEDRIC CARTER OST kinds of trees in Illinois are subject to one or more dis- eases. Some diseases cause little or no damage to affected trees. Others, by severely injuring leaves, twigs, branches, or roots, cause stunting or, eventually, dying of the trees. The most virulent or destructive diseases, such as elm phloem ne- crosis, Dutch elm disease, and oak wilt, usually cause rapid dying. The value of trees for shade and ornamental purposes on lawns and in recreation areas, for windbreaks, for erosion con- trol, or for lumber and other wood products may be greatly re- duced or destroyed by disease. Also, the removal or destruction of trees killed by disease may be very costly to home owners, park districts, forest preserve districts, or municipal govern- ments. Tree diseases that are of frequent occurrence in Illinois, or that are widespread or destructive here, are described in this publication. Included are diseases of both native and introduced trees. Information is given on prevention or control of these diseases. WHAT PRODUCES TREE DISEASES? Tree diseases are caused by living organisms, called infec- tious agents, or by nonliving objects or unfavorable environ- mental conditions, called noninfectious agents. In a broad sense, disease in trees and other plants is any condition that alters or prevents the expected normal growth. Infectious Agents The infectious agents are fungi, bacteria, viruses, and mis- tletoes. Fungi.—The infectious agents causing the greatest amount of damage are fungi. Fungi do not contain the green coloring matter called chlorophyl and are unable to manufacture their own food. They obtain nourishment from other living plants or from dead organic matter. Fungi that grow on, or in, a living Ce 2 ILLINOIS NATURAL HISTORY SURVEY CIRCUEAR 46 ; ae oy ! Magn ¢ j % wr EES % 7 Q peo LES & @ a D4 Ove pe f- Fig. 1 (left).—Fungus mycelium is composed of fine, threadlike strands of entwined hyphae. Fig. 2 (center).—Fungi reproduce by means of spores, which are micro- scopic in size and which vary in color, shape, and number of cells. The spores in this picture are oval, colorless, single cells which are produced by the fungus that causes Dothiorella canker of oak. Fig. 3 (right) —Bacteria which cause plant diseases are very small, rod- shaped, single-celled organisms. plant are called parasites, and the living plant is called the host. Those that live on dead organic matter are called saprophytes. Fungi grow as very fine, threadlike strands, called hyphae, that branch and produce entwined masses of moldlike growth called mycelium, fig. 1. The mycelium may grow within the host, or it may develop as powdery or moldlike growth on the sur- faces of leaves or other parts of the host. Fungi reproduce by means of spores, which are microscopic in size and vary in color and shape, fig. 2. These spores may be carried from diseased to healthy trees by wind, rain, pruning tools, insects, and other agents. Bacteria.—Bacteria that cause tree diseases are single-celled, rod-shaped, microscopic organisms, fig. 3. They reproduce by simple division—one individual divides to become two individuals. Bacteria, like fungi, contain no chlorophy! and obtain their nour- ishment from other living plants or from dead organic matter. Also, like fungi, they may be carried from diseased to healthy plants by wind, rain, pruning tools, insects, and other agents. Viruses.—Viruses are infectious agents that are too small to be seen with the highest power of the conventional com- pound microscope. However, they can be seen with the electron microscope. They appear to be protein in nature and are capable of reproducing themselves in living hosts. Many viruses are carried from diseased to healthy plants by insects. They may be transmitted artificially when parts of diseased trees are grafted on healthy trees. CARTER: ILLINOIS TREES: THEIR DISEASES 3 Mistletoes.—Mistletoes, which are seed plants with green leaves, grow on trees, fig. 4. They obtain nourishment from the sap of trees by sending rootlike structures (haustoria) through the bark, fig. 5. Only one species of mistletoe, Phoradendron flavescens, is known to occur in Illinois. In southern Illinois, this mistletoe frequently is found grow- ing on elm and occasionally on oak, sycamore, black gum, honey locust. and maple. It occurs in 18 counties of southern Illinois; its range extends northward along the Wabash River into Clark County and northward along the Mississippi River into Randolph County. Mistletoe causes very little noticeable damage to trees in Illinois. Scattered clumps or bunches of mistletoe, conspicuous Fig. 4.—Mistletoe is a green, seed-producing plant that grows on living trees. It causes little noticeable damage to trees in Illinois. The two clumps of mistletoe shown above are on American elm. wre Fig. 5.—Mistletoe attaches itself to a living tree. It obtains nourish- ment from the sap of the tree by sending rootlike structures (haustoria) through the bark. 4 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 during the dormant season when trees are bare of leaves, may appear unsightly. However, mistletoe is famous for its senti- mental and decorative values at yuletide. Noninfectious Agents The noninfectious agents include internal physiological dis- turbances, weather or climatic troubles, chemical injuries, and mechanical injuries. Physiological Disturbances.—Diseases that arise within the plant itself are referred to as physiological disturbances or dis- Fig. 6—Yellowing and wilting of foliage on trees may be caused by root injury from excavation of soil. Such injury to elms may produce foliage symptoms similar to those of phloem necrosis. Mechanical injury of this kind may cause dieback of branches or death of trees. CARTER: ILLINOIS TREES: THEIR DISEASES 5 orders. They frequently result from adverse growing conditions external to the plant and especially from deficiencies, excesses, nonavailability, or improper balance of the mineral elements necessary for normal plant growth. A common type of physio- logical trouble in Illinois is chlorosis. Chlorosis frequently affects the pin oak, and it occasionally affects many other kinds of % ae oe a. ; ASAT i we es WEN ok, Fig. 7 (left).—Sapsuckers, in feeding on the sap of trees, make bands of conelike holes in the bark of branches and trunks. These holes become larger and somewhat rectangular or square, as shown in this picture, as the injured tree continues to grow. Branches and trunks girdled by numerous rows of these holes may die. Fig. 8 (right).—Mechanical injury to trees, especially to weakened or newly transplanted trees, may be caused by bark beetles, borers, and other insects. This picture shows galleries made by the smaller European elm bark beetle in a weakened elm. 6 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 trees. It is usually associated with nonavailability of iron in the soil. Weather or Climatic Troubles.—Excessive moisture, drought, or unfavorable temperatures that cause improper or abnormal growth are called weather or climatic troubles. While Fig. 9 (top).—Girdling roots have killed some of the bark at the base of the trunk of this maple, as shown by the brown discoloration of inner bark where a narrow strip of outer bark has been removed. White living bark is visible at the top of the area from which the outer bark has been re- moved. Girdling roots may be so injurious that affected trees may show gradual decline and finally die. Fig. 10 (bottom).—Trees used as posts for wire clotheslines or fences are in many cases girdled and killed by the wire. CARTER: ILLINOIS TREES: THEIR DISEASES 7 Fig. 11.—Trees, such as Chinese elm, with soft, brittle wood may be seriously damaged by coatings of ice. these troubles cannot be prevented, their detrimental effects can be reduced in many cases by treatment. Chemical Injuries.—Various chemicals, including weed kill- ers, fungicides, insecticides, and fertilizers, may cause tree injury when they are used improperly. However, injury can be avoided by proper care in the application of such materials. Occasion- ally injury is caused by illuminating gas and sulfur dioxide. Mechanical Injuries.—Mechanical injuries are caused by man, fig. 6, birds, fig. 7, or other animals, and by insects, fig. 8, as well as by forces or conditions not influenced or controlled by man. Many of these injuries occur to the exterior of the tree and especially to the trunk. Most of the injuries caused by girdling roots, fig. 9, axes or similar tools, ground fires, girdling wires, fig. 10, nails driven into signs on tree trunks, lawn mowers, and motor vehicles can be avoided. Most of the injuries caused by water, hail, ice, fig. 11, snow, wind, fig. 12, and lightning cannot be prevented by man. Damaged trees should be treated as soon as possible to reduce the amount of ultimate injury which might occur. Broken branches should be cut back to sound lateral branches or to where they are attached to the trunk. Injured bark should be cut back to uninjured bark. Exposed wood in wounds should be protected with wound dressing to prevent de- cay, as described in the section ‘‘Wound Treatment.” 8 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 12.—The force of wind in tornadoes uproots many trees each year and causes inestimable damage to wooded areas. The wooded area shown above contained mostly oaks. TYPES OF TREE DISEASES Tree diseases are frequently classified according to the part of the tree which they attack or affect. On this basis they may be divided into leaf diseases, stem diseases, vascular diseases, and root diseases. Leaf Diseases Leaf diseases may be caused by infectious or by noninfec- tious agents. Most infectious leaf diseases are caused by fungi. However, some are caused by viruses or bacteria. The infectious diseases may produce moldlike growths on the leaf surfaces, local lesions in the tissues, yellowing of the tissues between the veins, or death of entire leaves. Some of them may affect flowers, fruits, twigs, or young branches. They may cause very little permanent damage to deciduous trees unless infection occurs year after year. Severe leaf injury and defoliation for several successive years may weaken affected trees and make them more susceptible to attack by other diseases and by insects. Also, they CARTER: ILLINOIS TREES: THEIR DISEASES 9 may lower the resistance of trees to unfavorable weather condi- tions. Defoliation in late summer is less injurious than defolia- tion in early summer, since the annual tree growth is usually completed by late July. Defoliation of evergreens during a single growing season may cause severe dieback of branches or death of whole plants. The names of many leaf diseases are descriptive of the types of injury produced, such as powdery mildew, spot, blotch, blight, rust, scorch, and chlorosis. Leaf diseases common to most species of trees are powdery mildew, leaf spot, scorch, chlorosis, and those resulting from chemical injuries. Powdery Mildew.—This fungus disease, which usually ap- pears in late July and August, produces an unsightly gray to white powdery covering on the leaves of affected trees. In many cases, small black dots, fruiting bodies of the fungus, are visible on the powdery growth. Although most trees are susceptible to this disease, it occurs infrequently and usually causes very little noticeable leaf injury. It can be controlled by applications of a sulfur fungicide at 10-day intervals after the first appearance of the disease. The fungi that cause powdery mildew in Illinois, and the trees they affect, are as follows: Microsphaera alni on catalpa, chestnut, elm, honey locust, oak, sycamore, and walnut Microsphaera arineophila on beech Microsphaera elevata on catalpa Microsphaera diffusa on honey locust Phyllactinia corylea on ash, birch, catalpa, elm, and oak Phyllactinia suffulta on ash, birch, and catalpa Podosphaera leucotricha on crab apple Podosphaera oxycanthae on wild cherry and hawthorn Sphaerotheca lanestris (brown mildew) on white oak Uncinula circinata on maple Uncinula clintonii on linden Uncinula macrospora on elm Uncinula salicis on poplar and willow Leaf Spot.—Leaf spot diseases become conspicuous usually during July and August. Most of them are caused by fungi or by bacteria. Occasionally some of them deform or kill flowers, fruits, twigs, or young branches. Most leaf spot diseases develop as small, scattered, circular to oval, light to dark brown dead 10 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 areas on the leaves, fig. 13. Later, these spots may enlarge and unite to form large, angular to irregular dead areas. Minute black dots, fruiting bodies of the fungus, may appear embedded in tissues of the diseased areas. On leaves of some trees, spots may have red to reddish-brown margins, as on leaves of chest- nut, linden, oak, poplar, and redbud. On leaves of other trees the spots may be bordered by purple, as on ash, crab apple, and hawthorn. Spots on walnut leaves are large, dark brown, and round to oval. On cherry leaves the brown dead areas of tissue drop out in time, leaving a shot-hole appearance of the leaf. One leaf spot disease of crab apple and hawthorn produces minute purple specks soon after the leaves unfold; it is caused by the fungus Physalospora obtusa. The specks soon enlarge to form reddish-brown, circular to oval spots. After a few weeks, some of the spots may start to enlarge and to form concentric rings of dark brown, which give rise to the term frogeye. This fungus also produces black rot of fruit and cankers on twigs and branches. Species of fungi that cause leaf spot diseases in Illinois be- long to the following genera: Alternaria, Ascochyta, Cercospora, Coccomyces, Coniothyrium, Cylindrosporium, Dothiorella, Gloeo- sporium, Gnomonia, Leptostroma, Marssonina, Microsphaerella, Monochaetia, Phyllosticta, Physalospora, Septoria, and Venturia. The bacterium Xanthomonas pruni causes a leaf spot of choke- cherry. Several successive years of defoliation resulting from leaf spot diseases may weaken affected trees and increase their sus- ceptibility to other diseases. Such affected trees can be given plant food to stimulate vigorous growth. Leaves may be pro- tected against leaf spot diseases by fungicides. Fungicidal sprays recommended for the control of some common leaf spot diseases are given in table 1, pages 28 and 29. Two or three applications should be made at 14- to 21-day intervals. The first spray should be applied approximately 3 weeks before spots appear on leaves, about June 15 for most leaf spot diseases in Illinois. Infectious leaf diseases which affect one or a very few spe- cies of trees include leaf blotch, leaf blight, and leaf rust. Each of these diseases is described in the discussion of one of the trees on which it occurs. Scorch.—This noninfectious disease may occur on any kind of tree. Ash, elm, and maple are frequently affected by it. Scorch develops as yellowing or browning of tissues between CARTER: ILLINOIS TREES: THEIR DISEASES 11 Fig. 13 (left) —Leaf spot diseases produce small, scattered, circular to oval, brown dead areas in the leaves. Frequently two or more spots coalesce and form large, irregular diseased areas. On elm, shown in this picture, the leaf spot fungus produces numerous fruiting bodies on the brown dis- eased tissues; these fruiting bodies make the spots appear black and scab- like. Fig. 14 (right).—Scorch is a noninfectious disease which develops as browning or yellowing between the veins or along the margins of leaves, or as complete browning and withering of leaves. the veins or along the margins of leaves, fig. 14, or as browning and withering of entire leaves. It may be caused by internal physiological disturbances, such unfavorable weather conditions as low temperature or drought, girdling roots, or soil area too limited for good growth. Frequently, scorch develops in July and August when the roots are unable to furnish sufficient water to compensate for the moisture lost from the leaves during pro- longed dry periods. Drying winds when the temperature is high will increase the amount and severity of scorch. Trees affected with scorch may lose many leaves during late summer; usually they do not die. Trees in low vigor may be aided in overcoming scorch by being fed and watered. Sometimes it may be advisable 12 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 to remove interfering and weak branches from a tree and thereby reduce the total foliage load that must be supported by the root system. Chlorosis.—Trees suffering from lack of available nutrients such as iron, magnesium, manganese, boron, zinc, and nitrogen usually show abnormal color of the leaves or abnormal types of growth. Probably the most common type of deficiency disease is chlorosis, caused by the unavailability of iron. Chlorosis fre- quently occurs in oak, especially pin oak, and maple, and it oc- casionally occurs in other deciduous trees and in evergreens; in pin oak, it develops as yellowing of tissues between the veins of leaves, fig. 15. In a severe case, the leaves curl and turn brown along the margins, or they develop angular brown spots between the veins. Later the leaves and twigs may die; the affected tree may be stunted in growth or it may die. Chlorosis may develop because of unfavorable conditions for the utilization of iron in the tree or in the soil. Under alka- line conditions, iron changes to insoluble forms. Frequently trees recover from chlorosis when they are supplied with available iron. The iron may be sprayed on the leaves of an affected tree, introduced into the trunk, or added to the soil. Spraying the foliage usually corrects chlorosis of the leaves that are treated but is not likely to benefit leaves produced after the iron has been applied. A spray composed of 5 pounds of iron sulfate (ferrous sulfate) and 2 pounds of soybean flour in 100 gallons of water is most effective when applied in late spring or early summer, during the time that the leaves are increasing in size. Table 2 gives equivalent measurements for small quantities of spray. Introducing iron into the trunk of an affected tree may cor- rect chlorosis for several years. The tree may be treated through holes, each approximately one-half inch in diameter, bored in the trunk at an oblique angle; the holes should slant downward and penetrate the sapwood to a depth of only 1 or 2 inches. The iron may be placed in the holes as a dry powder in large gelatin capsules or forced into the trunk in water solution by use of spe- cial equipment. The usual dosage is 5 grams of iron sulfate per inch of trunk diameter. Best results from this method of treat- ing are obtained when the iron sulfate is applied before leaves appear in the spring. More lasting results are obtained if equal parts by weight of iron sulfate and sulfur are added to the soil. The sulfur is CARTER: ILLINOIS TREES: THEIR DISEASES 13 Fig. 15.—Chlorosis in mild form is indicated by a pale yellowish-green color of the leaf tissue and normal green color of the midribs and veins, as in the leaf on the left. More severe chlorosis, in which some areas of the leaf turn brown and die, is shown by the leaf in the center. Trees affected by chlorosis for many years may have leaves severely spotted and killed, as shown by the leaf on the right. Fig. 16.—Leaves of trees sensitive to 2,4-D injury grow long and narrow, and the veins become unusually prominent. The severely injured English elm leaves in this picture have become twisted and rolled. 14 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 added to acidify the soil. Iron is changed to soluble forms in acid soil. To stimulate growth of chlorotic trees, the iron sulfate (fer- rous sulfate) and sulfur should be supplemented with tree food, as described in the section “‘Feeding.”’ The iron sulfate and sulfur mixture is supplied at the rate of 1 to 3 pounds per inch of trunk diameter at breast height. The heavier rate of application men- tioned is for trees over 6 inches in diameter. Chelated iron and other specially prepared iron compounds have been recommended as being more effective than ferrous sulfate for correcting chlorosis of many kinds of plants. These types of materials are sold under various trade names and should be used as recommended by the manufacturers. Chemical Injury.—In recent years chemical injury to trees has become frequent largely because of the common and wide- spread use of chemical weed killers such as 2,4-D, 2,4,5-T, and ammate. Injury caused by spray drift or vapors of 2,4-D and 2,4,5-T appears as deformed growth or dying of trees. In mild cases of injury the leaves of some trees, such as elm, hackberry, hickory, honey locust, and oak, may become thickened and leathery; the tips and margins of the leaves may be cupped downward or the leaves may be rolled. More severe injury may cause leaves to grow long and narrow and the veins to appear unusually prominent. Severely injured leaves of cherry, birch, black locust, elm, fig. 16, hawthorn, honey locust, Russian olive, sycamore, and walnut may become twisted or rolled and appear boat shaped or curled into ram’s-horns. In time the leaves die. Many trees recover in succeeding years from mild injury caused by 2,4-D and 2,4,5-T. Feeding to stimulate growth may aid in their recovery. Severely injured trees may have many branches killed or the trees themselves may die. Injury to trees from applications of tree food, or fertilizer, has been observed on some trees, especially on oak affected with severe dieback of branches and on trees that have large areas of dead bark on the trunks. Such areas of dead bark, which may not show externally and may therefore be overlooked, usu- ally can be detected if the trunk of an affected tree is tapped with a knife or ax for evidence of hollow areas. Fertilizer injury is indicated by browning and yellowing of leaves, especially along the margins and between the veins, fig. 17. Young leaves may stop growing and appear dwarfed. Many fibrous roots may die. Loss of these roots greatly reduces the amount of food and water CARTER: ILLINOIS TREES: THEIR DISEASES 15 supplied to the foliage. Most mildly injured trees recover; many of them do not even lose their leaves. Most severely injured trees lose their leaves, and some of them die. Injury to trees from illuminating gas varies from mild to severe and is influenced by the amount of gas which reaches the roots from leaks in gas mains. Leaks are most apt to occur in old mains. It has been suggested that injury to the trees is caused by hydrogen cyanide, which forms hydrocyanic acid with water in the soil. Severe injury by gas usually shows as rapid wilting, browning, and death of leaves, fig. 18, followed by with- ering of branches and death of the affected trees. Bluish-black discoloration of small roots on some trees can be detected after a Fig. 17.—Injury to trees from applications of excessive dosages of fer- tilizer shows as curling, yellowing, browning, and stunting of leaves. Ir- regular areas of tissues along the margins and between the veins turn brown and die. The living tissues between the veins become yellowish green, and the leaves are stunted, as shown by the two leaves on the right in contrast to the uninjured leaf on the left. 16 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 18.—A tree severely injured by illuminating gas usually shows rapid wilting, browning, and death of leaves, followed by dying of branches and death of the tree. In elms, gas injury may be mistaken for phloem necrosis. the bark is removed. The inner bark of London planes may ap- pear water soaked and pink; and long, narrow cankers may form in the bark at the bases of the trunks. A gas leak sufficient to cause severe injury to trees will kill grass, weeds, and shrubs in the vicinity of the leak; from such a leak, a strong odor of gas usually can be detected in the air. Most gas companies have gas detecting machines which are very sensitive to even small quan- tities of gas in the soil. Mild injury by gas is more difficult to determine, since injury that is similar in appearance may be caused by some infectious diseases, nutritional deficiencies, high temperatures, too little or too much water, and internal physiological difficulties within the tree. Mild injury can be caused by leaks of 2 to 5 cubic feet of gas per day. A mildly injured tree shows irregular, yellow discoloration of many of the leaves, somewhat similar to that in chlorosis; discoloration is followed by premature falling of in- jured leaves and also of some green leaves. Later the tree pro- duces another crop of small, light green leaves, and some twigs and branches may die. A gas leak that results in only mild injury CARTER: ILLINOIS TREES: THEIR DISEASES jr to trees may or may not be sufficient to kill the surrounding grass and other plants. A tree that is not severely injured by gas may be saved by prompt treatment. The gas leak must be stopped, and the soil around the tree roots should have air forced into it to replace the gas. The day after aeration the soil should be thoroughly washed. A watering needle or lance may be used to supp!y sufficient water to saturate the soil and to force large quantities of the water out through the aeration holes and away from the root area of the tree. After the soil has returned to a normal air- water relationship, the tree should be fed. it may need to be fed annually for several years. Injury to trees from sulfur dioxide occurs in areas where industrial plants, in utilizing sulfurous materials, liberate sulfur dioxide into the air. Injury is most apt to occur in clear weather when the humidity is 80 per cent or above, when the air move- ment is less than 5 miles per hour, and when the concentration of sulfur dioxide in the air is 3 parts per million or greater. Symptoms of injury decrease with increase in distance from the source of trouble. Evergreens are more susceptible to this type of injury than deciduous trees, old or mature leaves are more easily injured than young or immature leaves, and weakened trees more read- ily burned than healthy, vigorous trees. Sulfur dioxide produces three types or degrees of injury: acute, chronic, and invisible. Acute injury may look worse than it is since the leaves of an affected tree show sharply defined discolored or bleached areas along the margins or between the veins. Acute injury caused by a single burn may retard growth, but usually an affected tree recovers from it. Repeated burning causes premature defoliation, which may be followed by reduc- tion in the amount of annual growth or by sudden death of the tree. Chronic injury develops more slowly and is less severe; leaves may be discolored but usually they remain on the tree, which is retarded in growth. Invisible injury causes slight re- duction in growth but does not cause visible injury to leaves. Stem Diseases Stem diseases, in branches or trunks, may develop as canker, dieback, gall, witches’-broom, or woodrot. 18 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Canker.—Canker diseases produce localized dead areas in the bark of twigs, branches, and trunks of affected trees. These areas are oval to elongate in shape and vary from 1 or 2 inches to 1 or more feet in length. Cankers may enlarge until they girdle the affected stem; that part of the stem beyond the girdle dies. Cankers may develop as conspicuous sunken areas, as dis- colored areas of bark that are not depressed, or as diseased areas Fig. 19 (top).—The conspicuous, depressed canker on this branch of Chinese elm is surrounded by callus. The diseased bark, in which black fruiting bodies of the fungus are visible, is cracked and sloughing from the wood. Fig. 20 (center).—Cankers may be evident only by discoloration of the bark or by the presence of bumps (pustules) in the diseased bark, as shown in this canker on mountain ash. In this canker, the underlying diseased bark shows alternate bands of light and dark brown in contrast to the white color of living bark. Fig. 21 (bottom).—Fruiting bodies of a fungus frequently break through the diseased bark surface and become conspicuous as black spots or bumps, as shown on this branch of red oak. CARTER: ILLINOIS TREES: THEIR DISEASES 19 so inconspicuous that they cannot be detected by examination of the surface of the bark. The diseased bark of conspicuous sunken areas becomes fissured and cracks away from the surrounding living bark, fig. 19. Ridges of callus may be produced by the living bark surrounding the cankerous area. On trees having light-colored bark, diseased bark that does not become depressed may turn reddish brown. Such cankers are conspicuous because of the abnormal color of the diseased bark. Inconspicuous can- kers may be revealed by removal of a thin outer layer of bark and exposure of the brown to black dead bark of the diseased areas, fig. 20. Some canker diseases may be indicated by the presence of fungus fruiting bodies in the diseased bark. These fruiting bodies may produce raised places or pustules in the bark, fig. 20, Fig. 22 (left)—Cankers which continue to enlarge year after year may result in severe girdling and subsequent death of affected trees. Fig. 23 (right)—Galls or tumors on stems of trees vary in size from small and relatively inconspicuous to very large and conspicuous. The large gall shown above is on a white oak. 20 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 24.—Crown gall occurs usually at the base of an affected stem or on the larger roots. The gall shown here is on a root. Fig. 25 (left).—This elm is affected with dieback, as shown by the many branches with dead tips. Fig. 26 (right) —Witches’-broom of hackberry is most conspicuous when the trees are without leaves. CARTER: ILLINOIS TREES: THEIR DISEASES 21 or they may break through the bark surface and beeome con- spicuous as black spots or bumps, fig. 21. Cankers confined to branches usually can be eliminated by removal of the affected branches. Some cankers on the trunks of trees can be successfully removed by surgery. Large or multi- Fig. 27.—Fruiting bodies or conks of the bracket-type, wood-rotting fungi frequently develop at wounds on the trunks or branches of trees. In- fection by fungi occurs through such wounds. This picture shows conks of the white mottled rot fungus on white ash. ple trunk cankers may result in severe girdling and subsequent death of affected trees, fig. 22. Gall.—Gall diseases, appearing as growths on tree roots or stems, may be caused by fungi, fig. 23, bacteria, fig. 24, or viruses that enter the trees through wounds. Development of galls interferes with sap flow and may cause stunting or death of trees. Wounds should be treated promptly to prevent infection. Dieback.—Dieback is the gradual dying of a twig or branch ‘from tip to base, fig. 25. Frequently it develops on trees that are severely affected by canker diseases, especially on those branches girdled by cankers. Dieback may develop also on trees affected by conditions that reduce the amount of food and water below the 22 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 minimum required for growth. Treatment for dieback includes removing all dead wood and supplying food and water to stimu- late growth. Witches’-Broom.—This disease produces broomlike growths, composed of clusters of shoots, on branches of affected trees, fig. 26. Usually the shoots in these clusters are dwarfed and grow from swollen or enlarged areas on the branches. The broom- like appearance is most conspicuous when the trees are without t Fig. 28.—Fruiting bodies of the mushroom-type, wood-rotting fungi may develop on the trunks of affected trees or in the litter around the bases of the trees. leaves. Witches’-brooms occur on both deciduous and evergreen trees; they are caused by fungi, viruses, mistletoes, insects, or mites. In [ilinois, witches’-broom of hackberry is common. Woodrot.—Woodrot diseases, caused by fungi, produce decay of the wood of trunks and large branches. Decay usually develops slowly and may not noticeably shorten the life of an affected tree. However, it causes serious losses in the produc- tion of lumber and other wood products. Most wood-rotting fungi produce fruiting bodies of the bracket, fig. 27, or mushroor (toadstool), fig. 28, type. Because these fungi enter trees mainls CARTER: ILLINOIS TREES: THEIR DISEASES 23 through unprotected wounds, it is important to treat wounds promptly to prevent infection. Vascular Diseases Most vascular diseases are caused by infectious agents (fungi, bacteria, or viruses) which invade the tree and develop in the sapwood or inner bark. These diseases may cause the leaves on one or more branches to wilt and die or the entire tree to die. Fungi and bacteria that cause wilt usually produce dis- coloration of the young sapwood, especially that of the current season wood. This discoloration, usually brown, may appear as streaks or as diffused discoloration of individual wood rings. Two destructive wilt diseases caused by fungi are Dutch elm disease and oak wilt. The only widespread and destructive wilt disease of trees caused by a virus is phloem necrosis of elm. Root Diseases Root diseases, some of which produce abnormal growths or tumors on the roots, may weaken or kill the roots of affected trees. Infectious agents that produce root diseases include fungi, bacteria, and viruses. Shoestring root rot, a fungus disease, is one of the common root diseases of trees that have previously been weakened or injured. Loss of roots from this disease de- prives affected trees of sufficient food and water for normal growth and frequently results in branch dieback and staghead, frontispiece. / ) DIAGNOSIS OF TREE DISEASES . In some tree diseases, the causes may be determined readily by careful examination of the affected parts. For example, the fungi that cause certain leaf diseases may produce conspicuous gray to white powdery growth on the surfaces of affected leaves or they may produce circular to irregular, brown, dead areas in the leaves. These diseased areas may have visible bumps or pustules in the affected tissues. In many other tree diseases, the causes are obscure and may not be found on or in the portion of a tree that shows disease. In wilt diseases, for example, the leaves wither and die, but the organism that causes wilt is in 24 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 | the sapwood of the stem. An accurate diagnosis can be made only after sufficient evidence and information about the tree and its surroundings have been obtained to develop a complete case history of the trouble. TOOLS AND THEIR USES diseased include pocket knife, hand shears, leather punch, saw, hatchet or ax, shovel, increment borer, reading glass or hand lens, and field glasses. The leaves and branches of small trees may be reached from the ground and examined for diseases. On | trees so tall that the leaves and branches cannot be reached from > the ground, injury to leaves, cankers on branches, or other dis- . eased areas frequently can be detected with field glasses. To determine the specific agent or type of agent causing the © trouble, it is necessary in most cases to obtain a sample or sam- | ples of the affected part. In some cases, suitable samples can be ! obtained with an extension pruner. These samples can be exam- . ined for bark troubles caused by diseases and mechanical injuries . and for discoloration in the sapwood caused by wilt diseases, in- cluding maple wilt, Dutch elm disease, and oak wilt. Bark sam-' ples from the trunk of a tree can be obtained with a knife, | hatchet, ax, or leather punch. Samples adequate for detecting j the symptoms of elm phloem necrosis, for example, can be taken } with the punch, which does not injure the sampled tree exces- | sively. A punch, size 8, 10, 12, or 14, makes a small, round hole | that is soon plugged with callus tissue. For diagnosis of some tree troubles, it is desirable to obtain — samples of the trunk wood. A core or boring of wood, fig. 30, can f be obtained from the trunk of a tree with an increment borer. ) . Tools, fig. 29, useful for examining trees suspected of being The amount of wood produced each year by the tree will be indi- cated by the width of each annual wood ring on the core. Exam- ination of the core can determine whether growth has been normal each year, whether it has decreased or increased over a ~ period of years, whether it has stopped abruptly in the current © year. A gradual decrease in the amount of wood produced each — year may be caused by grade changes of the earth near the tree, limited space for root growth, girdling roots, root injury from — excavation or other soil disturbances, or root diseases. A shovel ‘ is useful for making examinations for various root troubles. 1 CARTER: ILLINOIS TREES: THEIR DISEASES 25 Fig. 29.—Tools useful in examining trees for diseases include knife, hand shears, saw, hatchet or ax, reading glass, hand lens, extension pruner, punch, increment borer, field glasses, and shovel. 26 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 30.—These cores or borings of wood, from the trunks of different trees, are marked to show the amount of wood produced each year. The core with broad annual rings of wood is from a healthy, fast-growing elm. The core with narrow rings is from an elm which grew slowly for many years and which had numerous branches dying during the last 6 vears of growth. The fast-growing elm produced as much wood in 10 years as the slow-growing elm produced in 40 years. During the period when branches were dying on the slow-growing elm, the amount of wood produced in 6 years by this tree was equal to the amount of wood produced in 1 year by the fast-growing elm. TREE THERAPY Spraying, pruning, feeding, watering, and sanitation are treatments used in combating tree diseases. Some diseases may be avoided by use of resistant or immune varieties of trees. The effectiveness of a spray may be increased by elimination of the source of the infectious agent that the spray is designed to control and by removal and burning of diseased twigs and branches. Removal of a few trees in dense plantings, to increase aeration, may aid in controlling some diseases. Trees severely weakened by repeated attacks of disease may be given plant food to stimulate vigorous growth. Since many diseases controlled by fungicides do not cause serious damage each year, it is not necessary to spray annually for their control. For this reason, the accompanying spray chart, table 1, does not represent a spray schedule to be followed each year. It is given to show the relationship between the time of year and the approximate time at which sprays should be ap- plied for control of certain tree diseases under Illinois condi- tions. The diseases are listed in the order in which they occur CARTER: ILLINOIS TREES: THEIR DISEASES 27 during the growing season. Since sprays are applied to the sur- faces of plants, they act as barriers or protectants against germs and are of major importance against leaf diseases. Equivalent measurements for small quantities of spray are given in table 2. Spray Materials Most sprays contain materials poisonous to man and other animals and should be used in the manner and at strengths recommended by the manufacturers or as specified in table 1. Copper Sulfate and Hydrated Lime.—In combination with water commonly called Bordeaux mixture. Copper sulfate can be purchased as crystals, granules, or powder. The powder is most convenient for use in spray mixtures. The instant method of mixing Bordeaux is commonly used. To prepare 100 gallons of an 8-8-100 formula of spray, fill the sprayer tank two-thirds full of water. Start the agitators and keep them running while slowly sifting in 8 pounds of copper sulfate and then 8 pounds of lime. Finish filling the tank with water. Use the spray mixture immediately. A sticker, such as soybean flour, 4 ounces to 100 gallons of spray, will increase the effectiveness of Bordeaux and other copper sprays. Copper compounds, sold under various trade names, may be substituted for Bordeaux mixture. Cycloheximide.—An antibiotic fungicide sold under such trade names as Acti-dione and Actispray. It kills the spore horns on the galls of the cedar-apple and cedar-hawthorn rusts. On juniper it should be applied after the spore horns appear on the galls but before they become gelatinous. DDT.—A chlorinated hydrocarbon insecticide. Special for- mulations of DDT are recommended for the control of the insect vectors of Dutch elm disease and phloem necrosis. Several con- centrates of these formulations are on the market. Applications of foliar DDT sprays over a period of years may bring about population increases of certain harmful insects and mites. Other chemicals may be needed to control these pests. DDT is haz- ardous to birds; in its use special care should be exercised to hold bird losses to a minimum. Feeding stations, watering places, and other places frequented by birds should be protected from spray drift and run-off, which should be held to a minimum. Methoxychlor can be substituted for DDT. 28 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Table 1.—Spray chart for some important diseases of Illinois trees. SEASON PLANT DISEASE November- March April April April- May April- May April- May April- May Elm Hawthorn, crab apple, eve: Juniper Sycamore Juniper Pine, spruce, Douglas fir Pine MATERIAL IN 100 GALLONS oF WATER NUMBER OF SPRAYS Days BETWEEN SPRAYS Dutch elm dis- Special DDT or ease (bark beetle) Rusts Rust Anthracnose Twig blight Tip blight Needle blight methoxychlor formulations (pages 27, 30, 64) Ferbam (Fermate or Niagara Car- bamate), 1% |lb.; wettable sulfur, oulbs or Thiram (Thylate Thiram Fungicide), 2 |b. Cycloheximide (Acti-dione or Actispray), 50 (380 mg.) tablets Organic mercury (Puratized Agri- cultural Spray, 114 pt. first spray, 1 pt. second spray, or Coromerc, 11% lb. first spray, 1 lb. second spray) Organic mercury (Puratized Agri- cultural Spray, 1 pt., or Coromerc, 1 |b.) or Copper sulfate, 8 lb.; hydrated lime, 8 Ib. Organic mercury (Puratized Agri- cultural Spray, | pt., or Coromerc, 1 lb.) or Copper sulfate, 8 lb.; hydrated lime, 8 lb. Organic mercury (Puratized Agri- cultural Spray, 1 pt., or Coromerc, 1 Ib.) or Copper sulfate, 8 lb.; hydrated lime, 8 Ib. bo 10-14 wn don 1h. Dias ans edt ete ee 10 10-14 | | | 21 CARTER: ILLINOIS TREES: THEIR DISEASES Table 1.—(Concluded.) 29 SEASON PLANT DISEASE MATERIAL IN 100 GaLLons or WATER April- May April- June May- June May- June June- July Maple, willow Tar spot Crab apple, Seab hawthorn, mountain ash Horse- Leaf blotch chestnut, buckeye Ash, maple, Anthracnose oak Elm Black leaf spot Walnut Leaf spot Elm Phloem necrosis (leafhopper) Juniper Rusts Organic mercury (Puratized Agri- cultural Spray, 1 pt., or Coromerc, 1 lb.) or Copper sulfate, 8 lb.; hydrated lime, 8 lb. Organic mercury (Puratized Agri- cultural Spray, 1 pt., or Coromerc, 1 lb.) or Dodine (Cyprex), 1 lb. Ziram (Zerlate), e sior Zineb (Parzale or Dithane Z-78), 11% bb. Organic mercury (Puratized Agri- cultural Spray, 1 pt., or Coromerc, 1 lb.) or Copper sulfate, 8 lb.; hydrated lime, 8 Ib. Organic mercury (Puratized Agri- cultural Spray, | pt., or Coromerc, 1 lb.) or Dichlone (Phygon XL), 1 |b., or Copper sulfate, 8 lb.; hydrated lime, 8 lb., or Wettable sulfur, 3 lb. Organic mercury (Puratized Agri- cullural Spray, 1 pt., or Coromerc, 1 |b.) Special DDT or methoxychlor for- rmulations (pages 27, 30, 69) Ferbam (Fermate or Niagara Carbamate), 14 lb.; wettable sulfur, 3 Ib. NUMBER iw) bo bo Days | BETWEEN SPRAYS | ~ — 14 10-14 10-14 14 35-40 30 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Table 2.—Equivalent amounts of chemical compounds for 100 gallons and 1 gallon of spray. CHEMICAL MatTeErIAL IN 100 MATERIAL IN | CoMPouND GALLONS OF WATER GALLON OF WATER Cycloheximide 50 (380 mg.) tablets 14 (380 mg.) tablet Soybean flour 4 ounces 14 teaspoon Ferbam lg pound 14 teaspoon Organic mercury 1 pint 1 teaspoon Dichlone 1 pound 1 teaspoon Dodine 1 pound 1 teaspoon Zineb 1/4 pounds 11% teaspoons Ziram 1/4 pounds 11% teaspoons Thiram 2 pounds 2 teaspoons Wettable sulfur 3 pounds 1 tablespoon Copper sulfate 8 pounds 2 tablespoons Hydrated lime 8 pounds 4 tablespoons Note: Teaspoon and tablespoon measures are for level full and are approximate equivalents. Dichlone.—A fungicide sold under the trade name Phygon XL. It controls black leaf spot of elm when it is used under Illinois conditions. Dodine.—A fungicide recommended for the control of scab of crab apple, hawthorn, and mountain ash. It is sold under the trade name Cyprex. Ferbam.—A fungicide sold under such trade names as Fer- mate, Karbam Black, and Niagara Carbamate. It is used for the control of rusts on juniper, hawthorn, and crab apple. Methoxychlor.—A chlorinated hydrocarbon that can be sub- stituted for DDT. It is more expensive than DDT, but it is much less toxic to birds and other warm-blooded animals. Organic Mercury.—A fungicide sold under such trade names as Puratized Agricultural Spray and Coromere. It controls syca- more anthracnose and some other leaf diseases under Illinois conditions. Sulfur.—A fungicide that can be obtained in several forms. Sulfur is sold under various trade names. Thiram.—A fungicide sold under the trade name Thylate Thiram Fungicide. It is reeommended for the control of rusts on crab apple and hawthorn. Zineb.—A fungicide sold under such trade names as Parzate and Dithane Z-78. It controls leaf blotch of buckeye and horse- chestnut. a | | CARTER: ILLINOIS TREES: THEIR DISEASES 31 Ziram.—A fungicide sold under the trade name Zerlate. It is recommended for the control of leaf blotch of buckeye and of horsechestnut. Feeding To maintain the health and to promote vigorous growth of shade and ornamental trees, it often becomes necessary to pro- vide food materials which are lacking from, or are present in insufficient amounts in, the soil. In the forest, where humus accumulates year after year, trees are liberally supplied with organic material derived from decaying leaves and plants. This material serves as food and helps to retain soil water. Since, along city streets, in lawns, or in parks, natural sources of food and water often are insufficient, artificial feeding and watering are frequently necessary. Three chemical elements, nitrogen, phosphorus, and potas- sium, must be available in the soil to insure the best develop- ment of a tree. A complete food for shade trees should supply all three. Nitrogen can be supplied by inorganic compounds— nitrate of soda, ammonium sulfate, calcium nitrate—or by or- ganic materials—urea, soybean flour, cottonseed meal, tankage, dried blood, pulverized sheep manure. Phosphorus can be fur- nished as superphosphate and potassium as muriate of potash. Although an effective tree food can be prepared from inorganic materials alone, it is believed that more lasting effects are ob- tained when one-third to one-half of the nitrogen is supplied by organic materials. There is no established rule as to the amounts of nitrogen, phosphorus, and potassium a tree food must contain. In ferti- lizer formulas, nitrogen is expressed as nitrogen (N), phosphorus as phosphoric acid (P,0,), and potassium as potash (K,0O). Com- monly, tree foods contain nitrogen, phosphoric acid, and potash in proportions of 12-6-4, 10-8-6, 10-6-4, 10-3-3, or 8-5-3. Prepared tree foods can be purchased ready for use through local dealers in fertilizers. Deciduous Trees.—A common method of determining the amount of tree food needed is based upon the amount of nitrogen required to maintain uniform tree growth. Deciduous trees hav- ing trunks of less than 6 inches in diameter at breast height should receive one-fourth pound of available nitrogen per inch of 32 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 trunk diameter, and larger trees should receive one-half pound of available nitrogen per inch of trunk diameter. A tree with a trunk 4 inches d.b.h. requires one-fourth pound per inch, or 1 pound, of available nitrogen. To determine the number of pounds of a 10-8-6 formula tree food required to give 1 pound of availa- ble nitrogen, divide 1 by 0.10 (10 per cent available nitrogen). The amount of 10-8-6 tree food required is 10 pounds. A tree with a trunk 12 inches d.b.h. requires one-half pound per inch, or 6 pounds, of available nitrogen. To determine the amount of a 10-8-6 formula required to give 6 pounds of available nitro- gen, divide 6 by 0.10 (10 per cent available nitrogen). The amount of 10-8-6 tree food required for the tree with the 12-inch trunk is 60 pounds. Fig. 31 shows one way of applying food to a tree. With a punch-bar or auger, drive holes, 114 to 2 inches in diameter, per- pea og 21 ne Ye IDS nM GETS NINN Fig. 31.—Dry tree food may be supplied to a tree through holes in the soil arranged in concentric circles around the trunk. These holes, 14% to 2 inches in diameter, 18 to 24 inches deep, should be 24 to 30 inches apart. CARTER: ILLINOIS TREES: THEIR DISEASES 33 pendicularly into the soil beneath the tree. The holes should be 18 to 24 inches deep and spaced 24 to 30 inches apart in concen- tric circles around the trunk. The outermost circle should be somewhat beyond the limit of branch spread and the inner circles should be spaced to maintain the required distance between the holes. Holes may be within 3 to 5 feet of the trunks of trees to supply feeding roots there. Distribute the tree food evenly in the holes. Then fill the holes with water and keep them filled for about 3 days to soak the tree food into the soil and make it quickly available to the feeding roots. The holes may then be filled with sand, peat moss, or loose soil. Or they may be left open to facilitate water absorption during rains, aerate the soil, promote development of feeding roots, and provide an effective means of supplying water during droughts. Tree feeding can be done at any time of year, but feeding during April, May, October, or November, when the soil contains ample water, is especially beneficial. Tree foods are most readily available when in water solution; hence it is highly desirable that, at the time of application, sufficient water be present in the soil to dissolve the food. Well-fed trees seem to be more resistant to drought than those that lack proper nourishment. Evergreens.—Although the above information on feeding applies specifically to deciduous trees, many of the directions apply also to evergreens. For evergreens growing in beds or closely planted in rows, apply soybean or cottonseed meal at the rate of 5 to 6 pounds per 100 square feet of ground area, or apply 10-6-4 or 8-5-3 tree food at the rate of 2 to 4 pounds per 100 square feet. The tree food should be worked into the topsoil with a hoe or soaked in with water. Specimen evergreens of such kinds as pine, spruce, fir, and cedar can be fed tree foods recommended for deciduous trees. For shrubby types, apply one-half to 1 pound per plant twice a year, in early spring and about June 15. For large specimen trees, apply 2 to 214 pounds of tree food per inch of trunk diam- eter. Place the tree food in holes beneath the branch spread in early spring or in the fall. With a soil auger or punch-bar, make 15 holes, 12 to 15 inches deep and 114 to 2 inches in diameter, for each inch of trunk diameter at breast height. Liquid Feeding.—Effective results are obtained with spray- ers, fig. 32, which develop sufficient pressure to force a liquid tree food into the soil. The only special piece of equipment needed is 34 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 aa ee OE OES RY t . 4 : Fig. 32.—Hydraulic sprayers which develop several hundred pounds pressure can be used in liquid feeding of trees. a feeding gun or lance, fig. 33, which replaces the ordinary spray gun. A feeding lance may be devised by almost anyone handy with tools, or it may be purchased from a seed store, hardware store, or arborist supply store. Liquid feeding can be done from early spring until late fall. The tree food should be released in the soil 12 to 18 inches below Fig. 33.—Feeding guns or lances can be devised by an ingenious indi- vidual who wishes to apply liquid plant food to his trees. Several types of these devices are manufactured and can be purchased. CARTER: ILLINOIS TREES: THEIR DISEASES 35 the surface. Injections should be made 4 to 6 feet apart in con- centric circles around the trunk of the tree. The outer circle of injection holes should be somewhat beyond the limit of branch spread, and the innermost circle of holes should be about 3 to 5 feet from the trunk. Tree foods consisting principally of soluble forms of nitro- gen, phosphorus, and potassium should be used in liquid feeding. Some of the tree foods for liquid feeding contain nitrogen, phos- phoric acid, and potash in proportions of 23-21-17, 21-18-17, 20-20-20, 19-28-14, or 15-15-15. The tree food is added to water in the spray tank. Then trees are fed the necessary number of gallons of solution to supply the required amount of food. The manufacturers’ recommendations should be followed in applying these tree foods. One to 3 pounds of these soluble tree foods per 5 inches of trunk diameter at breast height appear to be safe dosages. Methods of determining the amount of tree food needed for the less highly soluble materials, such as 10-8-6 and 10-6-4, are the same as described above for feeding deciduous trees. Watering Although shade trees generally do well in Illinois without special watering, lack of water in drought years or as a result of temporary or permanent lowering of the soil water table can cause serious injury and bring about death of the trees. Water- ing the ground surface beneath trees does little good. But ap- plying water through a grid of holes reaching to the root level (holes such as are required for tree feeding) is effective. Water- ing lances, fig. 33, offer a convenient means for soaking the soil around tree roots. Generous waterings at 2- to 3-week intervals give better results than frequent light waterings. Pruning Pruning can be done to improve the shape and general ap- pearance of trees, to remove branches and stems damaged by wind, ice, and other types of mechanical agents, and to eliminate diseased and dead twigs and branches. In pruning branches, avoid ugly wounds caused by splitting of wood and tearing of bark. In removing branches too large to hold with one hand, make three separate cuts as shown in fig. 34. First, make the 36 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 34.—The method of pruning branches shown here will avoid tear- ing the bark and making ugly wounds on trees. The first cut is made at A, the second at B. The third cut, at C, is made flush with the trunk of the tree. undercut, A, 12 to 18 inches out from the main stem. Then make the overcut, B, 2 to 3 inches farther out. These two cuts will cause the branch to break off by its own weight. Complete the pruning by the final cut, C, which removes the stub flush with the main stem. Avoid tearing the bark down at the bottom of the final cut. Protect the wound with a wound dressing. Most wound dressings are composed mainly of asphaltum. Pruning by topping or dehorning, fig. 35, is more detrimental than beneficial to trees. It stimulates abundant sucker or water- sprout growth that produces a thick crown of slender, weak branches. It creates large wounds which do not callus over. The wood exposed by these wounds is subject to wood rot. Sanitation As generally understood, sanitation consists of removal and destruction of dead or diseased trees or tree parts that may serve as breeding material for infectious agents or for insects that carry infectious agents. It is an important part of disease con- trol. In the control of some diseases, sanitation includes re- moval of one of the alternate hosts of the diseases. For exam- ple, currants and gooseberries are removed in the control of white CARTER: ILLINOIS TREES: THEIR DISEASES EW] pine blister rust since the white pine blister rust fungus must go to currants or gooseberries before it can reinfect white pines. Wound Treatment Wounds resulting from mechanical injuries or canker dis- eases can be treated as follows. Remove all of the diseased or injured bark, fig. 36. With a chisel, remove all discolored wood and sufficient living bark from around each wound or diseased area to give an oval or egg-shaped area of exposed wood, fig. 37. The long axis of the oval area should be lengthwise of the stem, since bark grows laterally over wounds. Paint the cut edges of Fig. 35.—Topping or dehorning usually is more detrimental than bene- ficial to trees. 38 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 36 (left)—When a canker is removed, the diseased area should be traced back to living bark. Edges of the living bark should be painted with shellac or wound dressing to prevent drying of living tissues. Fig. 37 (right)—After the edges are painted, all of the discolored or diseased bark is removed with a chisel or other sharp tool. the bark with shellac or wound dressing immediately after shap- ing the wound to prevent drying and injury of the living bark. As soon as the material applied to the edges of bark is dry, use denatured alcohol to disinfect any exposed wood from which cankers have been removed. After the disinfectant has dried, paint the exposed wood with wound dressing, fig. 38. Wounds may need to be repainted once or twice a year to insure complete protection from wood rot fungi and other wood-destroying agents, fig. 39. Disinfect tools used in pruning diseased trees to prevent spreading infectious agents to other trees. Denatured alcohol, used as a spray or dip, is a satisfactory disinfectant. Resistance and Immunity Whenever it is feasible to do so, species of trees resistant or immune to diseases should be used. Spiny Greek juniper, Hill CARTER: ILLINOIS TREES: THEIR DISEASES 39 Fig. 38 (left).—The exposed wood is disinfected with denatured alcohol and painted with a wound dressing. Fig. 39 (right)—Wounds may need to be repainted once or twice each year with a wound dressing to prevent wood rot fungi from attacking the exposed wood. This picture shows fruiting bodies of the wood-rotting sulfur fungus growing on exposed wood of a wound which has been treated with only one application of a wound dressing. juniper, and Keteleer red cedar are reported to be resistant to juniper blight. Other selections of red cedar have been reported that show resistance to cedar-apple rust. Varieties of chestnut have been developed which are resistant to chestnut blight. The Buisman elm is resistant to Dutch elm disease. Diseases for which resistant varieties or selections of trees are being tested include oak wilt, elm phloem necrosis, white pine blister rust, mimosa wilt, and poplar cankers. ARBOR-VITAE Arbor-vitae or white cedar trees are relatively free from parasitic diseases but are affected occasionally by winter drying. Winter Drying.—This trouble, frequently called winter in- jury, appears in late winter or early spring. It develops as ex- 40 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 tensive browning and death of foliage on 1l-year-old or older shoot growth. Often it kills branches and, occasionally, entire trees. Winter drying frequently appears after periods of rapid changes in temperature, especially when a rapid rise in tempera- ture has been accompanied by drying winds. As the air tem- perature rises, an excessive amount of water is given off through the needles. When water in the stem of a tree or in the soil around it is frozen, an insufficient amount of water is obtained through the roots to replace the water given off by the needles. Lack of water in the plant creates a form of drought which re- sults in winter injury. Mulching in early fall to prevent deep freezing and to maintain a sufficient amount of water in the soil will aid in preventing winter injury. Small trees in windy or sunny locations may be protected from wind or sun by shields of burlap or other suitable material. Injured trees should be given plant food, as described in the section ‘‘Feeding,” to stimulate growth. Dead wood should be removed after buds open in spring. ASH Ash trees occasionally are affected with anthracnose, leaf spot, powdery mildew, rust, wood rot, and a few minor canker and dieback diseases. Anthracnose.—Ash anthracnose, caused by the fungus Gloeosporium aridum, results chiefly in destruction of leaf tissue. It produces large, irregular brown areas, especially numerous along the margins of the leaves. It is neither abundant nor de- structive in Illinois during most years, and, except in unusual cases, requires no treatment. It can be controlled by sprays of organic mercury or copper fungicides, table 1. One or two ap- plications of spray should be effective. Leaves from affected trees should be burned in autumn to eliminate the main sources of overwintering inoculum. Scorch.—Many ash trees show leaf scorch annually, espe- cially trees growing under adverse conditions. Some affected trees may lose their leaves and appear dead by August. Scorch is discussed under “‘Types of Tree Diseases.” Feeding and water- ing to stimulate root growth and pruning to reduce total foliage growth may aid trees to overcome scorch. Rust.—Rust, caused by the fungus Puccinia peridermio- spora, occurs occasionally on leaves of ash trees, but it is usually CARTER: ILLINOIS TREES: THEIR DISEASES 41 of very little significance. It causes distortion of leaves and swelling of twigs. The alternate hosts of this rust are marsh and cord grasses. Rust appears infrequently and causes insufficient damage to require control treatment. Eradication of marsh and cord grasses near ash trees will disrupt the life cycle of the fungus. ; Cankers.—Three fungi, Physalospora obtusa, Cytospora sp., and Phomopsis sp., cause canker diseases of ash. Frequently, these fungi attack the trunks and branches of weakened trees and cause severe damage. Healthy trees usually are not affected by them. Dying of portions of branches, of entire branches, or of entire sections of affected trees may be an indication of canker disease. Affected trees may be saved if given food and water to stimulate more vigorous growth in early stages of the disease. Affected branches should be removed and burned. The diseased portion of an affected branch is indicated by discolored or dead bark or by streaks in the wood, especially in the current-season wood. White Mottled Rot.—This disease, caused by the fungus Fomes applanatus, is a white mottled rot of the heartwood of both green ash and white ash. It occurs on many other hard- wood trees and on some evergreens. It affects the trunks and branches of mature trees and dead trees. In early stages of the disease, small areas of the wood of affected trees are discolored brown. White spots soon appear in the discolored wood. In ad- vanced stages of the disease the affected wood is soft, crumbly, and straw colored, mottled with white. The fungus produces large, woody fruiting bodies or conks on trunks of affected trees, fig. 27. It enters the trees through stubs left by the breaking off of dead branches and through wounds of various kinds. All dead and dying branches should be carefully removed in such a way as to prevent further infection, and all wounds should be protected with a wound dressing, as de- scribed in the sections “Pruning” and “Wound Treatment.” Ad- ditional applications of wound dressing may be needed annually. BIRCH Birch trees weakened by infestations of bronzed birch borer or by unfavorable environmental conditions frequently are at- tacked by canker-producing fungi. 42 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Cankers.—Several fungi, Cytospora ambiens (Valsa am- biens), Melanconium betulinum, Nectria ditissima, N. cinnaba- rina, Sphaeropsis alnicola, and Valsa betulina, may cause cankers on trunks and branches of birch trees. Melanconium canker oc- eurs most frequently and may contribute to the death of indi- vidual branches or entire trees. Canker diseases frequently can be overcome by the cutting out of diseased parts, followed by the feeding and watering of affected trees to stimulate vigorous growth. However, trees se- verely affected and trees growing in unfavorable sites probably will not respond favorably to treatment. BUCKEYE AND HORSECHESTNUT Buckeye trees and horsechestnut trees in Illinois are affected almost every year by leaf blotch, but they are relatively free of other diseases. Occasionally they are affected by scorch. Leaf Blotch.—This disease is caused by the fungus Guignar- dia aesculi. It produces, on the affected leaflets, small to large, Fig. 40.—Leaf blotch of horsechestnut and buckeye causes small to large reddish-brown areas with narrow yellowish margins to form on in- dividual leaflets. CARTER: ILLINOIS TREES: THEIR DISEASES 43 irregular reddish-brown areas with narrow yellowish margins, fig. 40. The diseased areas of an affected leaflet may be confined to the margins or to tissues between the veins, or they may cover most of the leaflet, including midrib, veins, and tissues between the veins. In time, the whole leaflet may turn brown and fall pre- maturely. Fruiting bodies of the fungus appear as black specks on the diseased tissues. Trees severely defoliated for several suc- cessive years may become stunted. Two or three thorough applica- tions of a fungicide, either ziram or zineb, table 1, at 10- to 14-day intervals, will help to prevent defoliation. The first spray should be applied when the leaf buds are opening. Trees severely defoliated for several successive years can be given plant food to stimulate vigorous growth, as described in the section “‘Feed- ing.’ Leaves from affected trees should be burned in autumn to eliminate the main source of overwintering inoculum. Scorch.—Foliage scorch occurs on buckeye and horsechest- nut trees occasionally during July and August. It is most likely to occur on trees growing under adverse conditions. Scorch is described under ‘Types of Tree Diseases.” Feeding and watering may aid trees in overcoming the effect of scorch. CATALPA Catalpa trees occasionally are affected by powdery mildew and leaf spot. However, most damage to these trees is caused by a vascular disease called Verticillium wilt. Verticillium Wilt.—This vascular disease of western catalpa is caused by the fungus Verticillium albo-atrum. Affected trees may have one to several branches wilt occasionally or for sev- eral years in succession. Loss of many branches destroys the ornamental value of a tree. Some trees affected with wilt may die within 1 or 2 years; others may live for many years, fig. 41. The treatment for trees affected with Verticillium wilt is given in the section on maple. CHERRY Wild cherry trees are affected occasionally by leaf diseases and stem diseases. Rust.—The fungus Tranzschelia pruni-spinosae causes leaf rust on chokecherry, wild black cherry, and wild red cherry. The 44 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 small, dark brown to black spots produced on leaves are relatively inconspicuous. Rust causes insufficient foliage injury to require spraying. Brown Rot.—This disease, caused by the fungus Monilinia fructicola, produces a limited amount of blossom blight and twig dieback on wild black cherry. In blossom blight, the flowers turn brown prematurely and wither or appear soft and rotting. Twig dieback appears as drying and death of young twig tips. Cutting out affected branches as soon as they are found will usually give satisfactory control. Fig. 41.—Verticillium may cause foliage wilt on only a few or on all branches of an affected tree. However, affected trees may recover and not wilt again in succeeding years. This catalpa tree, which wilted in 1940, recovered from the disease and continued to live for many years. CARTER: ILLINOIS TREES: THEIR DISEASES 45 Twig Canker.—The fungus Valsa leucostoma attacks weak- ened cherry trees. It produces cankers and may kill inner shaded branches and branches weakened by injuries. Cutting out af- fected branches and stimulating vigorous growth by feeding and watering should overcome this disease. CHESTNUT Of the leaf and stem diseases that occur on chestnut trees in Illinois, chestnut blight is the most destructive. Chestnut Blight.—This disease, also called Endothia canker, is caused by the fungus Hndothia parasitica. One of the most Fig. 42 (top).—Cankers produced by chestnut blight appear as yellow- ish-brown, oval to elongate areas on smooth-barked stems of American chestnut. The canker in this picture is swollen, and cracks have formed in the diseased bark. The small bumps or raised spots in the bark are fruiting bodies of the chestnut blight fungus. Fig. 43 (bottom)—Cankers on Chinese chestnut most often appear on young trees growing in sites that have high humidity and poor circu- lation of air. These conditions frequently prevail in nursery plantings. 46 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 destructive tree diseases in North America, it has practically eliminated the American chestnut from the eastern United States. Development of chestnut blight is indicated by yellowing and browning of leaves on affected twigs and branches. Dead leaves and burs cling to diseased branches and are conspicuous during the dormant period. Young cankers develop as yellowish- brown, oval to irregular areas on smooth-barked, vigorous-grow- ing young stems, fig. 42. They appear as brownish, discolored, circular to irregular dead areas with slightly depressed or raised margins on slow-growing or old stems with smooth bark. Gir- dling of stems by these areas results in death of the parts beyond the affected regions. Usually trees die within 3 or 4 years after they have become diseased. No effective control has been devel- oped for chestnut blight. The varieties of chestnut which are resistant to blight are more suitable for ornamental plantings and nut production than for forest trees. Other Cankers.—Two other canker diseases of chestnut trees have been observed in Illinois. One occurs on American chestnut and is caused by the fungus Phomopsis castanea. The other oc- curs on Chinese chestnut, fig. 43, and seems to be associated with a fungus belonging to the genus Fusicoccum; possibly it is Fusicoccum castaneum (Cryptodiaporthe castanea). Affected branches should be cut 1 or 2 feet below any evidence of infec- tion. In nursery and orchard plantings, trees should be spaced to allow for free movement of air. CRAB APPLE Crab apple is susceptible to powdery mildew, leaf spot, scab, rust, and canker diseases. Powdery mildew and leaf spot diseases are described in the section “Types of Tree Diseases.” Fire blight is the most destructive canker disease of crab apple. Scab.—This disease, caused by the fungus Venturia inaequa- lis, appears on both upper and lower surfaces of leaves, but it fre- quently appears first on the lower. It produces olivaceous to sooty or smudgy spots. These spots may continue to enlarge until occasionally a sooty growth covers the whole leaf surface. The disease may produce similar spots on blossoms and fruits. On fruits, the spots enlarge and become at first black. Later in the summer they become brown, with black margins, and corky. Two to four applications of organic mercury or dodine, table 1, CARTER: ILLINOIS TREES: THEIR DISEASES 47 Fig. 44.—On crab apple, cedar-apple rust produces raised, orange spots which may have dark brown centers. Severely affected leaves are distorted. Fig. 45.—Fire blight cankers are usually conspicuous because of the rough, scaly, depressed appearance of the diseased bark and the formation of fissures or cracks between the living and diseased bark. The canker shown in this picture is on crab apple. at 2-week intervals should control scab. The first application should be made as the buds are opening. Apple scab spreads most rapidly during cool, wet weather. Rust.—Cedar-apple rust, fig. 44, caused by the fungus Gymnosporangium juniperi-virginianae, and other rust diseases of crab apple are described in the section on juniper. Spraying for the control of these leaf diseases on valuable specimen plants may be desirable. The sprays recommended are ferbam or thiram, table 1. Four or five sprays applied at 7- to 10-day intervals are recommended. The first spray should be applied as the buds are opening. 48 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fire Blight.—This stem disease, fig. 45, caused by the bac- terium Erwinia amylovora, is described in the section on moun- tain ash. ELM Elms are subject to many diseases, some of which are among the most destructive of the tree diseases in the United States. Wetwood.—This vascular disease is caused by the bacterium Erwinia nimipressuralis. It occurs in many genera of trees, in- Fig. 46.—A section of elm trunk affected with wetwood shows dark brown diseased areas in isolated portions of some wood rings (as at A) and brown streaking in part of the current-season wood ring (as at B). CARTER: ILLINOIS TREES: THEIR DISEASES 49 cluding apple, birch, elm, fir, hemlock, maple, mulberry, oak, poplar, tulip, and willow. It is more widespread and causes more injury in elms, especially Asiatic elms, than in any other trees. Fig. 47.—Foliage wilt that occurs on some elms affected with wetwood cannot be distinguished from foliage wilt caused by some other wilt diseases, except by laboratory analysis. This elm shows wilt caused by wetwood. 50 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Wetwood is most conspicuous in the heartwood and in the sapwood that is more than 4 years old. It may appear as dark brown streaks or broken bands of discoloration in one or several wood rings, or in only portions of a single wood ring, fig. 46. The diseased wood is watersoaked, and sap oozes out when the wood is cut. Affected elms that exhibit wilting of twigs and branches, fig. 47, have brown discoloration in the current-season sapwood, and occasionally in the cambial region and inner phloem as well as in old wood. This discoloration appears usually as grayish brown streaks in the wilting branches, fig. 48, especially in the springwood, and is similar to discoloration caused by other wilt diseases of elm, such as Verticillium wilt, Dothiorella wilt, and Dutch elm disease. In the cambial region and inner phloem, the grayish-brown discoloration appears as short streaks or irregu- lar, elongate patches. In wetwood-affected tissues, gas is produced in large amounts by the action of the fermenting bacteria on carbohydrates and other materials in the trunk of the tree. This gas, confined in the trunk, causes abnormally high sap pressures to develop, fig. 49. Pressures up to 60 pounds per square inch have been re- corded. The gas contains approximately 46 per cent methane, 34 per cent nitrogen, 14 per cent carbon dioxide, 5 per cent oxy- gen, and 1 per cent hydrogen. It does not contain carbon mon- oxide or illuminants. Sap that accumulates in the diseased wood and produces the water-soaked condition gives rise to the name wetwood. This sap contains phosphates and an abundance of potassium. The fol- lowing elements and compounds have not been detected in the sap: calcium, chlorides, copper, iron, magnesium, manganese, sulfates, zinc, nitrates, nitrites, ammonia, starch, indole, erythro- dextrin, and reducing sugars. The wetwood sap and the water- soluble materials in wetwood-affected tissues of diseased elms are alkaline, while the water-soluble materials in the sapwood and heartwood of normal elms are acid in reaction. Abnormally high pressures caused by fermentation force the accumulated gas and sap out of the trunk through cracks in crotches and trunks, fig. 50, through wounds made by the re- moval of branches, fig. 51, or through other trunk injuries. This exuding of sap is commonly called fluxing. The sap or flux, as it oozes out of diseased wood, is colorless to tan but turns dark CARTER: ILLINOIS TREES: THEIR DISEASES 51 ‘ig. 48.—Brown streaks produced by wetwood in the young sapwood of elm, especially in the current-season springwood, is easily confused with similar brown streaks produced by other wilt diseases of elm. Fig. 49 (left) Abnormal pressures develop in the diseased wood of elms and other trees affected with wetwood. Many affected trees that do not flux have unusually high pressures, as shown in this picture. Fig. 50 (right).—Bleeding or fluxing through wounds, such as cracks in crotches, is the most common external evidence of wetwood in elm. 52 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 upon exposure to air. As abundant bleeding occurs, the flux flows down the trunk, wetting and soaking large areas of bark. When the fiux dries, it leaves a light gray to white incrustation on the bark, fig. 52. The wetwood flux, when it exudes from the tree, is toxic to the extent that it is capable of retarding or preventing callus for- mation, and it frequently kills the cambium at the base of a cut Fig. 51.—Fluxing sap, A, of wetwood-affected trees is sufficiently toxic to retard or prevent formation of callus and to kill bark at the base of prun- ing wounds, B, as shown where the outer bark has been cut away. where a branch has been removed, fig. 51, and around the trunk cracks through which it flows. Young shoots directly above flux- ing regions may wilt. Foliage and young shoots, and also the grass at the base of an affected tree, may be killed if the flux drops on them. Growth of air-borne bacteria and yeast in the fluxing sap may produce, around wounds, gray to brown, foam- like, ill-smelling, slimy masses called slime flux, fig. 53. Cracks develop in the wood probably during the winter months, at times when the temperature falls rapidly to very low points. Toxic sap from the wetwood-affected heartwood kills the cambium for some distance around these cracks, and the bark separates from the wood to form oval to elongate pockets, fig. 54. Cracks in the bark with flux oozing through them become ILLINOIS TREES: THEIR DISEASES CARTER te in- x dries, it leaves a light gray to wh s as streaks on the bark of trunks and branches. etwood flu Fig. 52.—When w crustation that appear 54 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 apparent in June or July. Many such cracks callus over during the growing season in which they are formed. These cracks will not flux in succeeding years if the callus tissues produced are strong enough to withstand the pressure that develops in the dis- eased wood. On elms affected with wetwood, wilt, fig. 47, occurs when sufficient quantities of the toxic sap that has accumulated in the Fig. 53.—Air-borne bacteria, yeast, and other fungi may grow in the sap exuding through wounds of wetwood-affected trees and produce gray to brown, foamlike, ill-smelling, slimy masses called slime flux. trunk wood is carried into the branches. First, affected leaves curl upward along their margins, then the petioles become flaccid, and a short time later the leaves droop. Curl and droop are fol- lowed by wilt. Some leaves that wilt rapidly may drop to the ground while they are still green. Other leaves that wilt rapidly may take on a dull, greenish brown or somewhat bronzed appear- ance by the time they fall. Leaves that wilt slowly may turn yel- low or brown before they fall. Many of the brown leaves may CARTER: ILLINOIS TREES: THEIR DISEASES 55 AEE AAR ROO e Fig. 54—In elms suffering from wetwood. toxic sap of the diseased wood oozes out through cracks in the trunks, kills the cambium, and causes the bark to separate from the wood. In this picture is shown the trunk of a wetwood-affected tree from which part of the bark has been cut away. The toxic sap has oozed out through the crack (dark line indicated by arrow) and killed the surrounding cambium; the bark has separated from the wood to form an elongate pocket. 56 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 55.—Wetwood of elm may cause browning of tissues between the veins and along the margins of leaves. remain on the affected branches for several weeks. Leaves on | some trees may droop and turn yellow but not wilt, while those on others may turn dull greenish brown between the veins, fig. 55. Many leaves that turn yellow or dull greenish brown may abscise prematurely during July and August. Wilting as the result of wetwood in the trunk has been ob- © served on trees as much as 10 inches in diameter breast height, — but most frequently on trees 3 to 6 inches d.b.h. Elms more than | 10 inches d.b.h. affected with wetwood usually do not wilt but fre- — quently develop yellowing and browning of the foliage, and, later, © leaf drop and branch dieback. General decline may occur in these larger trees affected with wetwood. Branches that wilt on wetwood-affected trees show streaks | in the current-season wood, fig. 48. These streaks are especially | noticeable in the springwood. They originate in the trunk and — spread out into the branches. However, they usually do not reach — the branch tips. Where grayish-brown streaks are abundant, © CARTER: ILLINOIS TREES: THEIR DISEASES 57 they may appear as solid brown rings in the wood of one or more seasons, but usually only in current-season wood, which may appear water soaked when freshly cut. Affected branches may die. In some trees affected with wetwood, only a few branches die each year, and the trees show gradual decline. A tree wilting from wetwood should be examined for wounds through which toxic sap or flux is exuding. Such wounds may be in the affected branches, or in the trunk below the af- fected branches. A hole bored in an affected branch or trunk below a fluxing wound will allow the flux to escape and will pre- vent further oozing of flux through the wound. A drain pipe, if properly inserted in the hole, will prevent the flux from coming in contact with the cambial region and flowing over the outer surface of the bark. This treatment prevents additional toxic sap from being taken into the current-season wood and should pre- vent additional wilt. Many branches on which leaves have wilted do not die but produce a new crop of leaves later in the growing season or the following growing season. Since the wetwood organism is usually widespread in the trunk and old branches, the remova! of wilted branches will not eliminate the disease. Pruning of the tree can be delayed until the following spring, when all dead wood can be removed. Frequently this delay in pruning overcomes the ap- parent need for the removal of entire branches and may prevent destroying the ornamental value of the tree. Feeding will stimu- late vigorous growth and may aid wetwood-affected trees to over- come the adverse effects of the disease. Special care should be taken to properly drain the toxic sap from a tree affected by wetwood. In some cases, tapping the trunk of a large elm at its base has stopped the fluxing of sev- eral wounds along the trunk. Usually, more effective drainage of the accumulated gas and sap from the diseased wood is ob- tained if the tree is tapped a short distance below the fluxing region. Fluxing wounds, where branches have been removed, usually can be drained through a hole bored three-eighths to one-half inch in diameter, 6 to 14 inches directly below the fluxing region, fig. 56. Fluxing cracks in trunks and in branch crotches may or may not respond to a similar treatment. In some cases, several holes may have to be bored before satisfac- tory drainage is obtained. The crack in the wood may not be di- rectly behind the fluxing area in the bark. It may be so located 58 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 that a hole bored directly beneath the bark crack will miss the wood crack, and proper drainage will not result. As a rule, it is best to bore the hole to one side and about 6 to 14 inches below the fluxing crack, figs. 57 and 58. This hole should be directed ‘*—DRIPPING SAP Fig. 56.—Fluxing at pruning wounds may be stopped by a hole bored into the diseased wood where toxic sap and gas have accumulated. The hole should be 6 to 14 inches directly below the wound and slanted so that the toxic sap will flow out through the opening. A short piece of pipe, inserted in the hole only far enough to be firm, will carry the toxic sap away from the tree. CROTCH CRACK PIPE, : = DRAIN CROTCH PIPE—,. CRACK DRAIN HOLE Fig. 57.—Fluxing at cracks in branch crotches usually can be stopped by a hole bored into the diseased wood. The hole should be bored to one side and 6 to 14 inches below the base of the crack so that it will cross the crack in the underlying wood; it should be slanted so that the toxic sap will flow out through the opening. A drain pipe should be inserted in the hole. CARTER: ILLINOIS TREES: THEIR DISEASES 59 toward the probable location of the crack in the wood or toward the center of the heartwood. Drain holes should have sufficient slant to allow the wetwood sap to flow out, and they should extend through the heartwood to within a few inches of the bark on the opposite side of the trunk, fig. 59. A short piece of threaded pipe or electric conduit pipe should be screwed into each drain hole to carry the dripping sap away from the trunk and buttress roots. The pipe should be inserted TRUNK CRACK DRAIN HOLE (eon ele “eps Te, >, <—, ‘e-DRIPPING SAP Fig. 58.—Fluxing at cracks in bark of trunks should be treated as for eracks in branch crotches, fig. 57. The crack in the underlying wood may not be directly beneath the fluxing crack in the bark; the drain hole should be bored so that it will cross the crack in the wood. in the hole only far enough to be firm; it should not penetrate the water-soaked wood, fig. 59. If the pipe penetrates this wood, proper drainage will not result. Drain pipes should be exam- ined occasionally, and any accumulated slime found clogging the pipes should be removed. Trees treated with chemical compounds should not be pro- nounced cured unless the wetwood organism in the treated trees has been killed. Whether a tree has been cured can be deter- mined by laboratory tests on specimens from the water-soaked heartwood and sapwood. Suitable samples can be obtained with an increment borer. If the bacterium is still alive in the diseased wood, although the bleeding has been stopped by the treatment, the tree has not been cured; only the bleeding has been arrested. Some wetwood-affected trees overcome fluxing, at least tem- porarily, by sealing the wounds with callus growth. 60 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 59.—This section of a tree shows a drain hole bored at the proper angle to insure effective drainage and the drain pipe so inserted that it does not penetrate diseased wood (arrows) and interfere with drainage. Verticillium Wilt.—This vascular disease, caused by the fungus Verticillium albo-atrum, is described in the section on maple. Fig. 60.—Soon after Dothiorella cankers of elm are formed, fruiting bodies of the fungus appear as black, raised pustules in the dead bark. Under moist conditions, spores of the fungus ooze out of the pustules and are deposited on the surface of the bark. CARTER: ILLINOIS TREES: THEIR DISEASES 61 Dothiorella Wilt.—The fungus Dothiorella ulmi, which causes this vascular disease, produces curling, yellowing, and wilting of leaves, followed by defoliation, development of cankers on branches, and dieback of affected branches. Diseased bark turns reddish brown and becomes shrunken. In time, black raised pustules of the fungus appear in the diseased bark, fig. 60. Brown streaks produced in the young sapwood of wilting branches may be confused with those caused by Dutch elm disease or Verticil- lium wilt. Dothiorella wilt can be controlled in its early stages if all diseased branches are cut off a foot or more below any evidence of brown streaking in the sapwood. Trees in low vigor should be fed. Spraying to prevent insect injury, as by spring canker worm, is important in preventing infections, especially in nursery plantings, since the fungus enters through wounds. Dutch Elm Disease.—This vascular disease, caused by the fungus Ceratocystis ulmi, in 1960 was known in 24 states. First reported in Illinois in 1950, it had spread to all 102 counties of the state by 1959. It affects all native and imported species of elm. The first symptoms of Dutch elm disease are wilting, curling, and yellowing of leaves on one or more branches, a condition often called “flagging.” These symptoms are followed usually by premature falling of leaves and death of wilting branches. Some affected trees may have a few branches wilt at a time, fig. 61, and may die slowly over a period of 1 or more years. Other trees may have most or all of their branches wilt at one time and may die within a few weeks, fig. 62. Brown streaking develops in the sapwood of wilting branches. In a cross section of a branch, fig. 63, this browning May appear as a series of dots in a single wood ring; in some cases, the dots are so abundant that the entire wood ring appears brown. Brown discoloration occurs most frequently in the spring- wood of the current-season growth. In trees that wilt in early summer, the brown discoloration may not be noticeable when the branch wood is examined in cross section. However, this discoloration is usually conspicuous as fine streaks on the surface of the wood when the bark is carefully peeled from a wilting branch. The outer surface of sapwood on trunks may be brown. The presence of brown discoloration in young sapwood is used in the field as a symptom of Dutch elm disease. However, this symptom cannot be taken as final proof of the disease, since 62 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 similar discoloration of the sapwood is produced by several other wilt diseases of elm. To determine which wilt disease is affect- ing an elm, it is necessary to make laboratory tests of specimens from the diseased tree. These specimens, one-half inch or larger in diameter and 8 to 10 inches long, should be obtained from liv- ing branches which show wilting leaves. Unless they show brown streaking in the young sapwood as described above, the fungus is not likely to be present. Specimens should be wrapped in wax paper or plastic, then in wrapping paper, or placed in a box, and Fig. 61 (left)—On most trees affected with Dutch elm disease, wilt appears first on one or a few branches. This initial wilting is followed by wilting of additional branches, and the tree may die in 1 or more years. Fig. 62 (right).—On some trees affected with Dutch elm disease, branches over an entire tree wilt at approximately the same time, and the tree may die within a few weeks. CARTER: ILLINOIS TREES: THEIR DISEASES 63 mailed to a laboratory specializing in diagnosis of tree diseases: in Illinois to the Natural History Survey at Urbana; in most other states to the agricultural experiment station of the respec- tive state. The Dutch elm disease fungus grows in the water-conduct- ing vessels of the sapwood, most frequently that of the current season. It can cause infection when it is introduced into the sap- Fig. 63.—In trees affected with Dutch elm disease, brown discoloration develops as streaks or as bands in the young sapwood. Similar discolora- tion develops in elms affected with Verticillium wilt and Dothiorella wilt. wood through wounds in the bark. In the United States, this fungus is transmitted from diseased to healthy trees principally by the smaller European elm bark beetle and to a lesser degree by the native elm bark beetle. The fungus can spread from dis- eased to healthy trees through natural grafts of roots or branches. How frequently this type of transmission occurs has not been determined. The European elm bark beetle has very few natural enemies in the United States and has spread rapidly over most of the region where elms grow. It breeds in weakened, dying, and dead elms, in elm stumps and woodpiles, and in weakened and dead branches of living trees. This beetle overwinters in the larval stage. The larvae complete their growth and transform into pupae in the spring when the weather is warm. The pupae soon transform into adults, which start emerging in May. In Illinois, emergence of the first generation of adult beetles reaches a peak 64 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 in June. In trees affected with Dutch elm disease, the fungus grows in the galleries made by the bark beetle larvae, and adults, after emerging from their pupal skins, carry the fungus on their bodies as they leave the galleries. These adult beetles fly to nearby living elms and feed in the crotches of young shoots. In feeding, they chew through the bark, making ideal places for the fungus to enter a tree. Fungus spores carried by the beetles are deposited in these wounds and possibly are absorbed into the sap stream of the tree. Once in the sap stream, the spores ger- minate and grow, producing, in a previously healthy tree, an in- fection that soon brings about wilting of the invaded branches. Thus, a new case of Dutch elm disease has occurred. The female beetles soon invade the bark of weakened trees or dead elm wood and lay eggs that produce the next generation of beetles, which will appear in 5 to 7 weeks. There are two generations of Euro- pean elm bark beetles each year in the midwestern states. Emer- gence of the first generation, which reaches a peak in June, is followed closely by emergence of the second generation, which reaches a peak in August. Since all of the beetles in a single gen- eration do not emerge at one time but over a period of several weeks, by the time beetles of the first generation cease emerging those of the second generation have started to emerge. Dutch elm disease has been held in check in some communi- ties by sanitation, which means careful, thorough, and prompt removal of all elm wood in which beetles can breed. Sanitation includes removal not only of all diseased elms but of all weak- ened, dying, and dead elms all elm wood piles, bark on stumps, and weakened and dead branches in healthy trees. Diseased trees should be removed before the beetles emerge. Trees that are found infested with beetles should be destroyed promptly. Beetle-infested trees that cannot be destroyed within a few yards of where they are standing should be sprayed with 1 per cent DDT in No. 2 fuel oil before they are hauled away for burning. This treatment is to prevent fungus-infested beetles from escap- ing and carrying the fungus to healthy trees along the route to the place where the diseased trees are burned. In addition to sanitation, spraying with special formulations of DDT or methoxychlor, table 1, can be used to assist in the pro- tection of healthy trees from Dutch elm disease. Although these insecticides will not give complete protection of all sprayed trees, when combined with sanitation they give the best protection CARTER: ILLINOIS TREES: THEIR DISEASES 65 known at present. They reduce the chances of infection by killing many of the fungus-bearing beetles before they can gnaw through the bark and deposit spores in the sapwood of healthy ng, aa ¥ ~ 3 os tes is A } 3 ae lit ss ee Be ee ee ee a, ee a Fig. 64.—High-powered mist blowers may be used to obtain adequate coverage of large elms with DDT or methoxychlor for protection against the insects which carry the Dutch elm disease fungus or the phloem necrosis virus. Thorough spraying of foliage and branch crotches of young shoots is very important. 66 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 twigs. A single dormant spray is recommended for elms sprayed on a community-wide basis. This spray should be applied at any time after the leaves have fallen, in late October or early Novem- ber, until new flowers or leaves appear, in April or early May. It should contain 12 per cent insecticide if it is applied with a mist blower, fig. 64, or 2 per cent insecticide if it is applied with a hydraulic sprayer, fig. 65. To obtain maximum protection of elms of special value, an additional spray may be applied after second growth of leaves occurs, usually late July in Illinois. The foliar spray should contain 6 per cent insecticide if applied with a mist blower or 1 per cent insecticide if applied with a hydraulic sprayer. DDT is hazardous to birds and it may bring about population increases of harmful insects and mites, as mentioned on page 27. Phloem Necrosis.—Phloem necrosis, caused by a virus, is a widespread and destructive vascular disease of American elm, in- cluding the Augustine ascending, Moline, vase, and _ holly-leaf varieties. The virus can infect the winged elm. In 1960 phloem necrosis was known to occur in 15 states; it was present in the southern two-thirds of Illinois and in a few isolated places in the northern third of the state. Earliest visible symptoms of phloem necrosis appear usually as drooping and curling of leaves, followed by yellowing and browning of leaves, and finally by defoliation of the affected tree. Most elms that show these leaf symptoms in June and July die in a single growing season. On elms which die within 2 or 3 weeks, the leaves do not droop and turn yellow, but wilt rapidly and turn brown; many remain attached to the branches, fig. 66. Many elms which show leaf symptoms after early August live over winter, produce a sparse crop of leaves the next spring, and die in late June or July. Since these leaf symptoms fre- quently can be confused with those caused by other elm diseases, field diagnosis of phloem necrosis is based on the color and odor of the inner bark. In an affected tree, the thin layer of inner bark in contact with the sapwood, especially that at the base of the trunk and in the buttress roots, becomes yellow to butter- scotch in color, fig. 67. Occasionally, dark brown to black flecks are evident in the butterscotch-colored bark. The butterscotch color can be detected only in freshly cut samples of bark, since the inner bark from both diseased and healthy trees turns brown within a few minutes after being exposed to air. The odor of CARTER: ILLINOIS TREES: THEIR DISEASES 67 wintergreen emanates from the butterscotch-colored bark of trees affected with phloem necrosis. Healthy elms may be protected from infection by a spray designed to control the leafhopper which carries the phloem necrosis virus from diseased to healthy trees. The spray formu- lations recommended for leafhopper control are the same as those recommended for control of the insect carriers of Dutch elm dis- LD ’ a her # 44 uy Fig. 65.—Hydraulic sprayers used in spraying elms with DDT or methoxychlor for control of insects that carry Dutch elm disease or phloem necrosis must have sufficient power to give thorough coverage of all parts of trees. Drenching that results in excessive run-off should be avoided. 68 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 ease. Trees should be sprayed twice during the growing season to obtain maximum protection from the leafhoppers. The first spray should be applied as soon as the spring leaf crop is fully mature, usually during June in Illinois. The second spray should be ap- ya ; fs thie wo 9 ppt 4 Fig. 66.—Foliage on elms which die rapidly from phloem necrosis turns brown and much of it remains attached to the branches. CARTER: ILLINOIS TREES: THEIR DISEASES 69 plied immediately after the midsummer or second growth of elm leaves has occurred, usually after July 15 in Illinois. Each spray should contain 6 per cent insecticide if applied by a mist blower, fig. 64, or 1 per cent insecticide if applied by a hydraulic sprayer, Fig. 67—The butterscotch color, produced in elms affected with phloem necrosis, is present in the thin layer of inner bark which is in contact with the wood. When a chip of bark and wood is removed from a diseased elm stem, the butterscotch color appears as a ring where the inner bark is in contact with the underlying wood. fig. 65. Either DDT or methoxychlor is effective against leaf- hoppers. DDT has certain disadvantages. It is hazardous to birds, and its use may result in increased populations of harmful mites and insects, page 27. The effectiveness of spraying to prevent the spread of _ phloem necrosis will not be known for a year after the spray pro- gram has been started, as trees are infected with the virus a year or more before they show the disease. No tree already infected with the virus when the sprays are applied will be benefited by 70 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 the sprays, which protect against infection only during the year or years in which they are applied. For continuous protection, trees must be sprayed each year. Success in preventing phloem necrosis depends on spraying with such absolute thoroughness that no leafhopper bred in a diseased tree is left alive long enough to feed on a healthy tree. In areas where both Dutch elm disease and phloem necrosis occur, healthy elms may receive protection from the European elm bark beetle and the elm leafhopper by being sprayed three times each year. The first spray is the same as the first spray for Dutch elm disease control and the second and third sprays are the same as the two sprays for phloem necrosis control. Sani- tation as recommended for Dutch elm disease control is exceed- ingly important where both diseases occur, because elms killed by phloem necrosis as well as by Dutch elm disease provide excel- lent breeding places for the European elm bark beetles which carry the Dutch elm disease fungus to healthy trees. HACKBERRY Hackberry is frequently affected by a disfiguring stem dis- ease called witches’-broom. Witches’-Broom.—This disease, which produces broomlike growths on branches, is common on hackberry, fig. 26, in Illinois. The cause of witches’-broom is not definitely known. However, a powdery mildew fungus, Sphaerotheca phytoptophyla, and a gall- mite in the genus Hriophyes are usually associated with the dis- ease on hackberry. In a hackberry affected with witches’-broom, the buds swell and open wider than is normal for them. Fre- quently the bud scales become distorted and enlarged. Shoots from the affected buds usually become dwarfed and grow in clus- ters. The twigs in each cluster are short and stubby, and the diseased leader fails to develop fully. An open type of broom is formed when a healthy leader has numerous short, stubby twigs produced around its base. Witches’-broom is more common and widespread on Ameri- can hackberry than on Chinese hackberry or Mississippi hack- berry. There is no effective control for this disease; however, if the brooms are objectionable to the owner of an affected tree, they can be removed by pruning, as described in the section “Prun- CARTER: ILLINOIS TREES: THEIR DISEASES 71 ing.” Feeding the tree to stimulate vigorous growth may be de- sirable; this is described under ‘‘Feeding.”’ HAWTHORN The two most destructive diseases of hawthorn in Illinois are rust and fire blight. Rust.—Three fungi, Gymnosporangium globosum (cedar- hawthorn rust), G. juniperi-virginianae (cedar-apple rust), and G. clavipes (cedar-quince rust) cause rust on hawthorns. Of the three rusts, cedar-hawthorn rust is most destructive to haw- thorn. These rust diseases are described under juniper. Haw- thorns can be protected from these rusts by sprays, as given in table 1. Fire Blight.—This bacterial stem disease, caused by Hrwinia amylovora, is described in the section on mountain ash. JUNIPER Several species of juniper, especially red cedar, are affected by rust diseases, including cedar-apple rust, cedar-hawthorn rust, and cedar-quince rust. Fig. 68.—Cedar-apple rust on juniper is conspicuous because of the corky, chocolate-brown, globular galls produced on twigs. During rainy periods in April and May, these galls are covered with numerous gelatinous finger-like orange horns. The numerous horns shown in this picture pro- trude from the gall, which is attached to a short piece of juniper branch. 1hz2 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Cedar-Apple Rust.—This disease of juniper is caused by the fungus Gymnosporangium juniperi-virginianae. It has apple or crab apple as an alternate host. On juniper, it infects leaves and twigs and stimulates them to form chocolate-brown, globular to irregular-shaped corky galls which measure one-eighth inch to 2 inches in diameter. These galls, also known as cedar apples, mature the second spring after infection of the leaves and twigs, when they develop gelatinous, finger-like, orange spore horns during rainy periods in April and May, fig. 68. As the spore horns dry up, the galls become woody and, in color, dark brown to black. Spores produced on the orange spore horns of the cedar gall infect leaves of apple and crab apple, where they produce orange spots. Spores produced in these orange spots infect leaves and twigs of juniper in late summer. Since cedar-apple rust requires juniper and apple or crab apple as alternate hosts, these hosts usually should not be grown within a mile of each other. In ornamental plantings, where alternate hosts are growing close to each other, protection can be obtained by fungicidal sprays. There are two periods when juni- pers may be sprayed for the control of rust. One period is in April or early May, when the orange spore horns appear on the cedar galls or cedar apples. The other is in July or August, when junipers are susceptible to new rust infections from spores pro- duced on diseased leaves of apple or crab apple. Cycloheximide, table 1, applied during the first period, after the spore horns have appeared and before they become gelatinous, will kill the horns and prevent spore production. Ferbam and sulfur, table 1, ap- plied during the second period will protect junipers from spores produced on the foliage of apple or crab apple. Cedar-Hawthorn Rust.—This leaf disease, caused by the fungus Gymnosporangium globosum, produces galls on juniper and leaf rust on apple, crab apple, hawthorn, mountain ash, pear, quince, and serviceberry. The galls on juniper are small and irregular in shape but similar in color and texture to the galls produced by cedar-apple rust. Only a few orange, wedge-shaped, gelatinous spore horns are produced on each gall. Spores pro- duced on these spore horns in April and May cause leaf rust on hawthorn and other deciduous hosts. On hawthorn, the disease appears as yellow- to orange-colored spots on the upper surfaces of leaves and as raised orange to brown spots, covered with hair- like appendages, on the under surfaces, fig. 69. If, in late summer, the spores produced on hairlike growths from the spots on haw- CARTER: ILLINOIS TREES: THEIR DISEASES 73 thorn leaves are carried by wind to leaves of juniper, these spores produce greenish-brown galls on the juniper. Because this rust requires both juniper and hawthorn or other pomaceous hosts in its life cycle, the fungus cannot per- petuate itself if the alternate hosts are separated by distances greater than the distances spores are carried by wind. Adequate protection usually is given by distances of a mile or more. Spray- Fig. 69.—Cedar-hawthorn rust produces yellow- to orange-colored, de- pressed spots on the upper surface of a hawthorn leaf (left), and raised, orange to brown spots, covered with short hairlike appendages, on the under surface of the leaf (right). Fig. 70.—Fruits of hawthorn affected with cedar-quince rust may be deformed in shape, dwarfed in size, and have orange to cream tubelike Structures projecting from their surfaces. 74 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 ing as recommended for cedar-apple rust will control cedar- hawthorn rust. Cedar-Quince Rust.—This fungus disease is caused by Gym- nosporangium clavipes. It produces swollen, elongate cankers on branches of juniper. A stem and fruit disease, it has ame- lanchier, apple, chokeberry, crab apple, hawthorn, fig. 70, Japanese quince, mountain ash, pear, or quince as an alternate — Fig. 71—Cedar-quince rust produces elongate, swollen cankers on branches of juniper. During rainy periods in April and May, orange ge- latinous masses of fungus spores break through the rough bark of these cankers. host. In rainy periods of April and May, orange gelatinous masses of spores break through the rough diseased bark of juni- per, fig. 71. These spores infect young stems and fruits of quince, hawthorn, and other pomaceous hosts. They produce long, slender, cream to white, tubelike structures on twigs and fruits, fig. 70. Diseased twigs are swollen and deformed. Diseased fruits are deformed and stunted. Bright orange spores from the tube- like structures on twigs and fruits reinfect junipers in late sum- mer. Spraying as recommended for cedar-apple rust will control cedar-quince rust. Juniper Blight.—This stem disease, caused by the fungus Phomopsis juniperovora, occurs most frequently on red cedar. However, it has been found on arbor-vitae, cypress, false-cypress, and other species of juniper. The fungus invades and kills the bark, and in time cankers form on the diseased stems. As the CARTER: ILLINOIS TREES: THEIR DISEASES 5 cankers enlarge, the affected stems die and the needles turn brown. Young trees that are affected may die. All diseased twigs and branches should be removed and burned. In nursery plant- ings, all affected plants should be destroyed. When available, re- sistant varieties such as Hill juniper, Keteleer red cedar, and spiny Greek juniper should be used. Spraying with organic mer- cury or copper sulfate and hydrated lime, table 1, may prevent infection. Five sprays applied at 10-day intervals are recom- mended. The first application should be made as soon as shoot growth starts in the spring. LINDEN Linden is relatively free of diseases; however, Verticillium wilt affects an occasional tree, and some affected trees die. Verticillium Wilt.—This vascular disease is caused by the fungus Verticillium albo-atrum. In linden, it causes leaf and branch wilt, which are accompanied by the production of brown streaks in the young sapwood of affected branches. These streaks are similar, except in color, to the green streaks that the disease produces in maple. General symptoms and control measures are those given for maple. MAPLE Most species of maple grown in Illinois are subject to leaf, stem, and vascular diseases. Anthracnose.—Anthracnose or leaf blight, caused by the fungus Gloeosporium apocryptum, develops in maple as small to large, circular to irregular, light brown areas of dead tissues. This disease may appear from late May to early August. Se- verely affected leaves may drop prematurely. Trees affected by anthracnose for a single year usually are not damaged suffi- ciently to require treatment. However, trees affected for several successive years may need feeding to stimulate vigorous growth and spraying with organic mercury or copper fungicide to pre- vent infection, table 1. Two applications of spray at 10- to 14-day intervals should give effective control. The first spray should be applied when the leaves are about half grown. Tar Spot.—Soft maple is most frequently affected by this leaf disease, caused by the fungus Rhytisma acerinum. Hard maple and red maple are affected only occasionally. The disease 76 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 appears first as yellowish-green diseased areas on the upper sur- faces of leaves. These areas, which are oval to irregular in shape, enlarge and become tarlike, thickened, and raised, fig. 72. The fungus lives over winter in the tarlike spots on fallen leaves and Fig. 72.—Tar spot of soft maple is conspicuous because of the black, glossy, raised, tarlike spots produced on the upper surfaces of affected leaves. produces spores which, when released during May and June, in- fect the new crop of young leaves. Tar spot can be controlled if infected leaves are raked and burned in the fall, and the new crop of leaves the following spring are sprayed with an organic mercury or copper fungicide, table 1. One spray should be ap- plied in early May, and, in unusually wet seasons, a second spray should be applied 3 weeks after the first spray. Scorch.—Foliage scorch is a common leaf disease on Norway maple and hard maple during June, July, and August. This dis- ease, fig. 14, is described in the section “‘Leaf Diseases.” Al- though it occurs on many maples each year, it does not cause affected trees to die. Canker and Dieback.—Canker and dieback of twigs and branches on maples have been associated with several fungi in Illinois: Steganosporium piriforme on hard maple and Norway maple, Nectria cinnabarina on sycamore maple, and Sphaerop- sis negundinis, Leptothyrium maximum, and Phacidium negun- dinis on box elder. These fungi attack weakened trees and kill CARTER: ILLINOIS TREES: THEIR DISEASES 77 twigs and small branches. Occasionally they develop on large dying branches. Affected trees should be given plant food to stimulate vigorous growth, and all affected branches should be removed. Verticillium Wilt.—This is one of the most destructive vas- cular diseases of maple. It is caused by the fungus Verticillium albo-atrum. In Illinois, Verticillium wilt is not confined to maple; it has been known to affect, and occasionally to kill, black locust, Fig. 73.—Maples affected with Verticillium wilt have green discolora- tion in the young sapwood, especially in the current-season wood. This green discoloration frequently appears as fine streaks. Occasionally it may appear as solid bands of green in individual wood rings. In trees of other kinds, the discoloration is brown. catalpa, elm, flowering almond, Japanese barberry, linden, privet, redbud, smoke tree, sumac, tulip tree, viburnum, and yellow- wood. Foliage of affected trees may wilt any time during the growing season. However, most affected trees wilt during late June, July, or August. On some trees only one to a few branches wilt, on others whole sections wilt, fig. 41, while on still others that are severely affected all branches wilt, and death of the trees follows. Some trees that show a limited amount of wilt may re- cover and not wilt in succeeding years. In maple, Verticilliwm produces fine green streaks in the young sapwood of wilting branches, especially in sapwood of the current season, fig. 73. In other kinds of trees, Verticillium produces brown to yellowish- brown streaks in the young sapwood of wilting branches. Since the fungus can live in the soil and invade the trees through the roots, the streaks in the sapwood spread from the roots up through the trunks and into the branches. The basal portions of wilting branches should be examined for the streaks, since these streaks may not extend to the tips of affected branches. Affected trees should be given plant food to stimulate vig- orous growth, as described in the section ‘“‘Feeding.’’ All dead 78 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 branches or dead wood on branches showing wilt should be re- moved. However, it is advisable not to remove live branches or twigs on which the leaves are wilting or have recently wilted. Many branches that show wilt may not die but may produce a new crop of leaves 3 or 4 weeks after wilt has occurred or by the following spring. Pruning will not eliminate fungus which is present in the trunks and roots of affected trees. MOUNTAIN ASH Leaves of mountain ash are occasionally affected with a fungus disease called scab. This disease is described in the sec- tion on crab apple. The most destructive disease of mountain ash in Illinois is fire blight. Fire Blight.—This bacterial disease, caused by Erwinia amylovora, produces branch and trunk cankers, fig. 45, twig blight or dieback, and blight of leaves, blossoms, and fruits of mountain ash. It affects other ornamental plants, also: coto- neaster, crab apple, fire thorn, Japanese flowering quince, rose, serviceberry, and spiraea. Leaves and blossoms of mountain ash affected with fire blight suddenly wilt and turn brown to black, as if scorched by fire. Affected twigs die. The disease may spread from diseased twigs to branches and produce extensive cankers. Cankers usu- ally are bounded by cracks between the dead and living bark. The dead bark usually turns reddish brown in color. Plants that have large cankers or diseased areas on their stems should be cut and burned. Those that show the disease on only scattered branches need not be destroyed, but the diseased branches should be removed and burned. Removal of all visible infection in a branch is possible if this branch is cut off 18 inches or more below the base of the external diseased area. Tools used in removing a diseased branch should be treated with a disin- fectant to prevent spread of the bacteria to other branches or trees. All large wounds should be painted with a wound dressing, as described under ‘‘Wound Treatment.’ Blossom blight and twig blight can be prevented or reduced by applying one or two sprays of copper sulfate, 4 pounds in 100 gallons of water, at 2-week intervals before buds open. Spread of twig blight during prolonged wet springs can be prevented by spraying with strep- tomycin as recommended by the manufacturer. The first spray CARTER: ILLINOIS TREES: THEIR DISEASES 79 should be applied as soon as twig blight appears and additional sprays at 7-day intervals until July 15. OAK The oak is subject to several destructive diseases. Oak wilt is the most destructive disease of oak in Illinois. Anthracnose.—This leaf disease, as caused by the fungus Gnomonia veneta, affects both white oak and sycamore. On white oak, anthracnose develops as irregular brown areas adjacent to and centering around diseased areas on the midribs and lateral veins of leaves. In some cases, the blades of most leaves of af- fected trees are killed, especially the blades of leaves on the lower branches. Dark brown fruiting bodies (pustules) of the fungus appear on the diseased areas of the leaves, especially on the mid- ribs and veins. These raised pustules or bumps can be seen with a hand lens and occasionally with the naked eye. The fungus may spread from the leaves into the twigs, where it produces cankers or causes twig dieback. Control for anthracnose on oak includes burning of diseased leaves and twigs and spraying of affected trees. All fallen leaves and twigs should be gathered and burned in the autumn. When- ever possible, diseased twigs should be removed and burned. Spraying with organic mercury or copper sulfate and hydrated lime is recommended for the prevention of leaf infection in the spring, table 1. The first spray should be applied when the leaves are about half grown. In wet springs, a second spray should be applied 14 days later. Oak trees that have been severely weak- ened by anthracnose over a period of years should be given plant food to stimulate vigorous growth, as described in the section “Feeding.” Leaf Blister.—Leaf blister or leaf curl, caused by the fungus Taphrina caerulescens, affects the various species of oak. Red oak is especially susceptible. Usually the disease appears only during cool, wet springs. Affected leaves show circular, raised, wrinkled, yellowish areas on their upper surfaces; the diseased areas appear as depressions on the lower surfaces of the leaves. Leaf blister seldom causes serious damage. It can be controlled by a spray of lime sulfur or of Bordeaux mixture (copper sulfate and hydrated lime, page 27). One spray applied before the buds open in the spring is recommended. 80 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Rust.—Leaf rust, caused by the fungus Cronartium quer- cuum, occurs infrequently on oak in Illinois. It produces small yellowish spots with brown, bristle-like tendrils on the under- sides of leaves. Usually it causes insufficient damage on oak to Fig. 74 (top).—Dothiorella cankers on oak develop as oval to elongate, dark brown, depressed areas in the bark of affected branches. A conspicuous ridge is visible between the diseased bark on the top and the living bark on the bottom of the section of branch in this picture. Fig. 75 (center).—Fruiting bodies of the Dothiorella fungus develop as pustules in the dead bark of oak and erupt through irregular openings in the outer bark. Fig. 76 (bottom).—In an oak affected with Dothiorella canker, the sap- wood beneath the diseased bark is discolored dark brown to black, and streaks of discoloration extend into the adjacent living wood. CARTER: ILLINOIS TREES: THEIR DISEASES 81 warrant control treatment. Several species of pine are the alter- nate hosts of this rust. Smooth Patch.—Smooth patch, sometimes called smooth bark or white patch, is a fungus disease of the outer bark of white oak. It causes the outer rough bark to slough and leaves irregular to circular, smooth, light gray, depressed areas in the bark on the trunk. These areas vary from a few inches to more than a foot in diameter and occasionally form a band around the trunk. The fungus Alewrodiscus oakesii is associated with this disease. It grows in the outer diseased bark and produces very small, cream-colored, cup-shaped, and somewhat leathery, mush- room-like fruiting bodies which appear during winter and spring. Since the fungus is confined to the outer, rough, dead bark, the disease does not retard growth of affected trees. Dothiorella Canker.—This stem disease, caused by the fungus Dothiorella quercina, is the most destructive canker disease of oak in Illinois. It affects twigs, branches, and occasionally the trunks of trees in both the white oak and red oak groups. Can- kers develop as dark brown, oval to elongate, sunken areas in the bark, fig. 74. Frequently, cracks form between the living and dead bark along the margins of the cankers. Soon after the bark has died, fruiting bodies of the fungus develop as pustules in the diseased bark. In time, they erupt through irregular open- ings in the bark, fig. 75, and spores, fig. 2, of the fungus ooze out on the surface of the bark. The young sapwood beneath the diseased bark is dark brown to black and shows streaks of dis- coloration that extend into the living wood beyond the area of diseased bark, fig. 76. Other fungi which may cause canker and dieback, especially of weakened oaks, include species of the following genera: Bul- garia, Coniothyrium, Coryneum, Cytospora, Diatrype, Fusicoc- cum, Nummularia, Phoma, Phomopsis, Pyrenochaeta, Sphaerop- sis, and Strumella. Oak Wilt.—This vascular disease, caused by the fungus Ceratocystis fagacearum, affects all of the important native oaks in the Midwest, fig. 77. Also it has been associated with bush chinquapin, Chinese chestnut, European chestnut, and tan-bark oak. It is the most destructive disease in oak woodlot and forest areas in the United States. Wilt of leaves usually appears first on branches in the upper portion of the crown of an affected tree. The wilt progresses 82 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Ts r 8 i” a Fig. 77.—Red, black, and other oaks in the red oak group, when affected by oak wilt, usually wilt and die over a period of several weeks or during a single growing season. In most cases, wilt of leaves appears first on branches in the upper portion of the crown of the affected tree. The wilt progresses downward and inward until all the foliage is affected. The tree in the center of this picture has many branches without leaves, and leaves on the remaining branches are wilted and dead. Located in Ingersoll Park at Rockford, this tree was the first oak in Illinois from which the oak wilt fungus was obtained. The tree, which died in 1942, showed brown streaking in the current-season wood typical of the oak wilt disease. CARTER: ILLINOIS TREES: THEIR DISEASES 83 Fig. 78.—In trees of the red oak group that are affected with oak wilt, brown to black streaks develop in the young sapwood of wilting branches. The normal white color of healthy sapwood is shown by the branch piece at top of picture. downward and inward until all of the foliage is affected. Leaves on trees in the red oak group become dull or pale green in color, and the margins may curl upward. These symptoms are followed by yellowing or bronzing of the leaf tissues; the discoloration spreads from the margins toward the midribs of affected leaves, which may fall at any stage of wilt. Mature leaves usually re- main stiff and fully expanded during the different stages of wilt and for some time after death. Immature leaves curl, droop, turn dark brown to black, and remain attached to the branches. Leaves on wilting bur oak and white oak usually turn light brown or straw color, curl, and remain attached to the branches. In trees of the red oak group, brown to black discoloration usually develops in the current-season sapwood of wilting branches. This discoloration may appear as streaks or as dif- fused browning of individual wood rings, fig. 78. Similar sap- wood discoloration has been observed occasionally in wilting bur oak trees. 84 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Affected trees in the red oak group may wilt and die in 4 to 6 weeks, or during a single growing season. Occasionally, large branches of trees infected late in the summer live over winter and produce a few scattered leaves before dying the following spring. Trees of the white oak group usually die slowly over a period of years. Control of oak wilt in localized areas has been obtained by the poisoning or removing of healthy oaks adjacent to diseased Fig. 79.—The oak wilt fungus can pass from a diseased tree to a healthy tree through grafted roots. Grafting occurs frequently between roots of trees which are within 50 feet of each other, especially trees in the red oak group. trees or by trenching between diseased and healthy trees. These treatments interrupt an extensive underground system of inter- grafted roots, fig. 79, through which spread of the fungus from tree to tree might take place. Removal of the first wilting branches in trees of the white oak group may keep the trees healthy for a few years, but these trees are subject to reinfection. Effective control measures to prevent the spread of oak wilt over long distances have not been developed. Squirrels and several kinds of sap-feeding insects are attracted to the mats of the oak wilt fungus which are produced beneath the bark of wilt-killed oaks, and it has been shown experimentally that these animals and insects can carry the oak wilt fungus on their bodies. Re- CARTER: ILLINOIS TREES: THEIR DISEASES 85 Fig. 80.—Fungus strands produced under the bark of oaks affected with shoestring root rot are slender, flattened, dark red, and rootlike in appear- ance. The shoestrings, or rhizomorphs, which grow in the duff and soil around diseased oak trees are black and round, and they measure about one-sixteenth inch in diameter. Fig. 81.—The white, fanlike growth of the shoestring fungus produced under the bark of diseased oaks is called a mycelial fan. 86 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 moval and destruction of diseased oaks before the fungus mats are produced will eliminate this important potential source of fungus inoculum. Shoestring Root Rot.—Many oak trees that show branch die- back and staghead, frontispiece, are affected with Armillaria or shoestring root rot caused by the fungus Armillaria mellea. This fungus produces two types of growth—slender, flattened, dark red, rootlike strands, fig. 80, and white mycelial fans, fig. 81, be- neath the bark of infected trees. The rootlike strands or shoe- strings which grow in the duff and soil around infected trees are round, black, and about one-sixteenth inch in diameter. Since weakened and injured trees are most susceptible to this disease, maximum protection can be obtained by avoidance of root in- juries and by applications of plant food to maintain vigorous growth, as described in the section ‘‘Feeding.”’ PINE Pine is affected occasionally by needle blight diseases and by a tip blight disease. The first known cases of white pine blister rust in Illinois were found in Jo Daviess County in 1946. Needle Blight.—This leaf disease, mainly of Austrian pine, is caused by the fungus Dothistroma pini. It appears in late sum- mer as slightly swollen, dark spots or bands on 1-year-old needles. The part of a diseased needle from the swollen area to the tip turns light brown and dies. The swollen areas, produced by growth of the fungus in the needles, do not enlarge during the fall and winter months. However, they begin to enlarge in March. By May they appear as dark brown to black, raised fruit- ing bodies visible through fissures in the needles, fig. 82. Spores produced in these fruiting bodies can cause new infections. Af- fected trees show sparse foliage, since the diseased needles drop prematurely. Spraying with organic mercury or copper sulfate and hy- drated lime during April and early May should control needle blight, table 1. The first spray should be applied about the mid- dle of April. In wet seasons, a second spray should be applied 3 weeks after the first spray. Needle Cast.—This leaf disease, caused by several species of fungi of the genus Lophodermium, produces reddish-brown spots or elongate areas on affected needles. Fruiting bodies of the asso- CARTER: ILLINOIS TREES: THEIR DISEASES 87 ciated fungus appear as small, black, oval spots on the diseased portions of needles, fig. 83. Needle cast seldom causes sufficient damage to warrant control treatment. Spraying with copper sul- fate and hydrated lime, as indicated for tip blight in table 1, has been reported to control needle cast. Needle Rust.—This fungus disease, mainly of red pine, de- velops in the spring as cream- to orange-colored, baglike pustules on needles, fig. 84. Of the fungi that cause needle rust, Coleo- sporium solidaginis is most important. Goldenrods and asters are alternate hosts of this fungus. Needle rust may cause defoli- Fig. 82.—Fruiting bodies of the needle blight fungus push out through fissures in diseased needles of Austrian pine. They appear as dark brown to black pustules or bumps. Fig. 83.—Fruiting bodies of the needle cast fungus appear as small, black, oval spots on diseased portions of pine needles. 88 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Fig. 84.—Conspicuous cream- to orange-colored, baglike, fruiting bodies attached to pine needles affected with rust contain numerous, orange, pow- der-like spores of the fungus. ation and stunt young pine trees, but it seldom causes much dam- age on older trees. Sooty Mold.—A heavy, sooty, threadlike growth or crust may appear on needles of pine, fig. 85, fir, and other evergreens, and on leaves of elm, linden, maple, tulip tree, and other decidu- ous trees. This growth, made up entirely of fungus material, may be in isolated patches or it may cover the entire needle or Fig. 85.—Sooty mold, which occurs on many kinds of trees, is conspicu- ous because of the black, threadlike growth or crust produced on the sur- face of leaves and twigs, as shown on this pine. This disease seldom causes serious damage. CARTER: ILLINOIS TREES: THEIR DISEASES 89 leaf surface. The fungi that cause sooty mold belong to the fam- ily Perisporiaceae. They grow as saprophytes on secretions (honeydew) produced by aphids and scale insects. Although sooty mold appears unsightly, it causes little if any noticeable damage to trees. Control of the insects will eliminate sooty mold. White Pine Blister Rust.—This stem disease, caused by the fungus Cronartium ribicola, is widespread in the north-central, northeastern, and northwestern parts of the United States. It has been found on white pine in the northern quarter of Illinois. The fungus invades and kills the needles. It grows from the needles into the bark of twigs and branches, where it produces Fig. 86.—The orange to yellow blisters or fruiting bodies of the white pine blister rust fungus are conspicuous during late spring. swollen, oval cankers. As these cankers enlarge, they girdle and kill infected stems. In late spring, orange to yellow blisters or fruiting bodies of the fungus break through fissures in the dis- eased bark, fig. 86. Spores produced in these fruiting bodies infect leaves of currants and gooseberries, plants that serve as alternate hosts. Small orange to yellow pustules are produced on the leaves of these shrubs during the summer. The spores pro- duced in these pustules cause new infections on white pines. A common recommendation for protection of white pines from blister rust is the eradication of all currants and goose- berries within one-half mile of the pines. However, in many situa- tions involving ornamental plantings such eradication may not be feasible. Recently, blister rust was controlled on western white pine by the antibiotic fungicide Acti-dione BR. Treatment of diseased trees included removal of dead and dying branches at their points of attachment. The pitch that had accumulated on the surfaces of cankers was removed. Each trunk and branch canker, the surrounding bark area, and branch stubs were then sprayed with Acti-dione BR. Information about Acti-dione for control of blister rust on pines should be obtained from the manufacturer. 90 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 Diplodia Tip Blight.—This stem disease, caused by the fungus Diplodia pinea, occurs frequently on Austrian pine, less often on Scotch, red, and mugho pines, and occasionally on Doug- las fir and blue spruce. It causes the needles to turn brown and the twig tips to die, fig. 87. Development of minute, black Fig. 87.—Drooping and dying of shoot tips and browning of needles of | spruce are typical of Diplodia tip blight. fruiting bodies of the fungus at the bases of needles that have | turned brown and in the bark of twigs that have died differen- | tiates this disease from frost injury and similar twig troubles. . Control of this disease requires first that all affected twigs | should be removed and burned. Additional protection may be ‘ obtained by sprays of organic mercury or copper sulfate and hy- | drated lime, table 1. Three applications of spray are recom- mended. The first spray should be applied as soon as new shoot | growth appears, the second when new shoot growth is about half | grown, and the third about 2 weeks later. Trees stunted by the disease should be given tree food to stimulate vigorous growth, as described under “‘Feeding.”’ POPLAR Some species of poplar, such as Lombardy and Simon, are frequently attacked by canker diseases and occasionally by rust and crown gall. Rust.—Larch rust, a leaf disease caused by the fungus Melampsora medusae, has poplar and larch as alternate hosts. It occurs occasionally in Illinois. On poplar, it produces yellow- | ish-orange, powdery pustules on the lower surfaces of leaves dur- ing the early summer. These pustules change to dark brown or black during late summer and autumn. They may be scattered, CARTER: ILLINOIS TREES: THEIR DISEASES 91 or they may be so closely crowded that the entire surface of an affected leaf appears powdery. Leaf rust usually causes insuffi- cient damage on poplar to warrant treatment. Cytospora Canker.—This stem disease, caused by the fungus Cytospora chrysosperma, frequently kills Lombardy and Simon poplars in Illinois. On young trees, cankers first appear as slightly sunken areas in the smooth bark of branches and trunks. These cankers are circular to oval or irregular in shape, fig. 88. They gradually enlarge until, frequently, affected stems are gir- dled and killed. As the cankers enlarge, the diseased bark be- comes brown and sunken. The fungus produces fruiting bodies which appear as pustules in the diseased bark. Spores of the fungus are produced in these fruiting bodies and under moist conditions they ooze out in slender, threadlike coils. These spores may be splashed by rain or carried by wind, birds, or insects to other trees. All dead and dying branches of affected trees should be removed. Trees affected with extensive trunk cankers may be cut and burned, or they may be subjected to careful surgery, fol- lowed by the use of a disinfectant, such as denatured alcohol. Surgery may prolong the lives of some severely affected trees. Wounding of trees should be avoided, since the fungus enters trees through wounds. Trees should be given plant food to main- tain vigorous growth, as described in the section “Feeding.” When it is feasible to do so, the planting of species of poplar most susceptible to this disease, such as Simon and Lombardy, should be avoided. Dothichiza Canker.—This stem disease, caused by the fungus Dothichiza populea, affects many species of poplar; it is most destructive on Lombardy poplar. It produces oval to elongate sunken cankers on the twigs, branches, and trunks. In time, the Fig. 88.—Elongate, depressed Cytospora cankers may girdle and kill affected stems of poplar. 92 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 diseased bark turns brown and cracks, and the underlying dark brown diseased wood is exposed. Callus tissues which form at the borders of the cankers tend to grow over the surface of the ex- posed wood. Trunks and branches girdled by cankers die. Young trees usually are killed by the disease. Older trees may not be killed but usually they are disfigured to the extent that they lose their ornamental value. The treatments recommended for trees affected by Cytospora canker usually are effective against this disease. Crown Gall.—This disease is described in the section on wil- low. REDBUD Redbud is affected occasionally by a canker disease and by — a wilt disease. However, these diseases are not necessarily fatal. Canker.—This stem disease, possibly caused by the fungus | Botryosphaeria ribis chromogena, has been seen on redbud in | several parts of Illinois. It causes cankers on branches and oc- casionally on trunks of affected trees. The cankers are produced . during May and appear as inconspicuous, oval, flattened areas. | They become elongate and sunken as they enlarge during June. Frequently cracks form between the living and dead bark. After — the cankers cease enlarging, callus tissues form along their mar- | gins and spread inward over the diseased areas. Small cankers | may be covered with callus tissues in a single growing season, | while large cankers may not be covered for several growing sea- sons. Affected branches show sparse foliage, and branches gir- | dled by cankers die. In most cases, this disease can be controlled by removal of the affected branches and by applications of plant food to stimu- late vigorous growth of the affected trees, as described in the section ‘‘Feeding.’’ In severe cases, it may be necessary to re- move the trees. Verticillium Wilt.—This vascular disease, caused by the fun- gus Verticillium albo-atrum, occasionally affects redbud and causes partial to complete wilt of branches. Part or all of a wilt- ing branch may die, and occasionally wilt-affected trees die. However, some trees may recover from this disease and not wilt in succeeding years. Treatment of trees affected with Verticil- lium wilt is described in the section on maple. CARTER: ILLINOIS TREES: THEIR DISEASES 93 SPRUCE The most destructive disease of spruce in Illinois is Cytos- pora canker. Occasionally spruce trees are affected by Sphae- ropsis tip blight. Cytospora Canker.—This stem disease, caused by the fungus Cytospora kunzei, appears most frequently on Norway spruce and Colorado blue spruce. Occasionally it attacks Koster’s blue spruce and Douglas fir. Browning of needles and dying of the low branches of affected trees are usually the first symptoms of Cytospora canker. As the disease progresses, it spreads to higher branches. In time, affected trees become unsightly and lose their value for ornamental purposes. The cankers produced are inconspicuous because the affected bark does not noticeably change color or become depressed. Fre- quently white patches of resin appear on the bark in areas where cankers have formed, fig. 89. Careful removal of a thin outer layer of bark in the area that separates diseased and healthy tis- sues will reveal tiny, black, pinhead-like fruiting bodies of the fungus in the diseased bark. These fruiting bodies contain mi- nute spores which can be spread by rain, wind, or pruning tools. The development of trunk cankers may result in girdling and death of affected trees. This disease, most common on trees over 15 years old, is known to occur on younger trees, also. Control of Cytospora canker requires that all diseased branches should be cut back to the nearest living laterals or to the trunk of the affected tree. Wound dressing should be applied to all pruning wounds, as described in the section ‘“‘Wound Treat- ment.” The bark should not be injured unnecessarily, since the fungus may enter through wounds resulting from injuries. When Fig. 89.—The occurrence of Cytospora canker on spruce is usually indi- cated by conspicuous deposits of resin on the bark. This resin frequently forms as a white incrustation. 94 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 the branches of affected trees are wet, spores ooze out from can- kers onto the surface of the bark. Pruning at this time should be avoided, since spores may be spread by pruning tools. Spray- ing the low branches and the trunks of affected trees and nearby healthy trees in the spring with organic mercury or copper sul- fate and hydrated lime may help to prevent spread of the dis- ease; sprays are the same as those for tip blight, table 1. Three or four applications of spray at 2- to 3-week intervals are re- quired. Since, it is believed, weakened trees are susceptible to this disease, feeding to stimulate vigorous growth, as described under “Feeding,” may help to combat Cytospora canker. Feeding will also stimulate new growth that may fill in vacant spots in the contour of trees on which surgery has been performed. Fig. 90.—Anthracnose of sycamore frequently causes severe defolia- tion and twig dieback early in the growing season. This type of injury is frequently confused with frost damage. => CARTER: ILLINOIS TREES: THEIR DISEASES 95 Diplodia Tip Blight.—This disease of spruce, pine, and Doug- las fir is described in the section on pine. SYCAMORE In most years, sycamore trees in Illinois are attacked by a leaf and twig disease called anthracnose. In some years the amount of injury produced is not conspicuous, but in other years the injury is so great and widespread that trees throughout the state are almost defoliated. Anthracnose.—This leaf and twig disease, caused by the fungus Gnomonia veneta, is also known as twig blight. It affects both sycamore, fig. 90, and oak. On sycamore, anthracnose may = Fig. 91.—In the early leaf blight stage of sycamore anthracnose, very young leaves are killed during April and May. The injured leaves fall, and a new crop of leaves is produced within 3 to 5 weeks. Defoliation from early leaf blight annually for several years may severely weaken affected trees. produce two types of leaf injury. One type, called early leaf blight, develops as complete killing of very young leaves during April or May, fig. 91. This type of injury may result in partial to complete defoliation and is occasionally confused with frost injury. The second type of leaf injury develops as small to large, irregular brown areas adjacent to and centering around diseased spots on the midribs and lateral veins of mature leaves, fig. 92. This type of leaf injury rarely causes defoliation. Dark brown fruiting bodies or pustules of the fungus appear on the dis- eased tissues, especially on the midribs and veins. These raised 96 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 pustules can be seen with a hand lens and sometimes with the naked eye. The fungus may spread from diseased leaves through twigs into young branches and produce cankers, fig. 98, or cause twig and branch dieback. Anthracnose usually causes most leaf injury and defoliation in wet seasons. Trees severely affected by anthracnose for sev- eral successive years may have many branches killed. Such affected trees should be given plant food to stimulate vigorous growth, as described in the section “Feeding.” Two applications of an organic mercury spray, table 1, will control anthracnose. The first spray should be applied when the buds are swelling and Fig. 92.—The second type of sycamore anthracnose leaf injury appears as small to large, irregular brown areas along the veins and midribs of mature leaves. This type of injury seldom causes serious defoliation. CARTER: ILLINOIS TREES: THEIR DISEASES 97 before the leaves unfold; the second spray should be applied 10 to 14 days later. Canker Stain.—Canker stain, caused by the fungus Cerato- cystis fimbriata f. platani, is a deadly stem disease of London Fig. 93.—The sycamore anthracnose fungus frequently spreads from leaves into twigs and branches and forms cankers on the branches around the bases of the diseased twigs. plane. Known principally in the eastern and southeastern parts of the United States, it has been reported in Missouri but not in Illinois. However, it could easily spread into the East St. Louis area from St. Louis, Missouri, where it has been known to occur. This disease has been reported on sycamore, which appears to be much less susceptible than London plane. It may affect either branches or trunks of trees. On London plane trees, it produces dark brown or black cankers on smooth bark. On old rough bark, diseased areas appear first as elongate depressions or furrows. Beneath these areas the inner bark is blackened and dead. The diseased areas continue to enlarge in succeeding years. The wood beneath the diseased bark is stained reddish brown or bluish black. The discoloration is most conspicuous in the wood rays and frequently penetrates to the center of the stem. Stems girdled by cankers die beyond the diseased areas. Special care must be exercised when pruning is done to con- trol this disease, since the fungus can be transmitted by pruning 98 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 tools, wound dressings, and any other agencies or operations that make contact with the fungus on diseased trees and then with wounds on healthy trees. Pruning should be done during the win- ter when the fungus is least active. All pruning tools should be carefully disinfected before being used on healthy trees. Dena- tured alcohol, 70 per cent, is a satisfactory disinfectant. Climb- ing ropes contaminated with the fungus can be disinfected by ex- posure to formaldehyde vapors for 3 hours (one-fourth pound formaldehyde in a 10-gallon closed container). Since the fungus can be carried in the ordinary types of wound dressings, gilsonite- varnish type of paint which has 0.2 per cent phenylmercury nitrate mixed in it should be used on wounds of trees being treated for this disease. WILLOW Willow is susceptible to leaf and stem diseases. Trees are not killed by the leaf diseases but may be killed by the stem dis- eases. Tar Spot.—This leaf disease is caused by the fungus Rhy- tisma salicinum, which produces jet black, thick, tarlike, raised spots on the upper surfaces of leaves. The spots caused by this fungus on willow are usually much smaller than the spots caused | by the tar spot fungus on maple, fig. 72. In Illinois, willow is |. usually not severely damaged by tar spot. The disease can be controlled by sprays of organic mercury or copper sulfate and hydrated lime, table 1. Two applications are recommended, the first application when the buds are opening; the second 3 weeks after the first. Raking and burning of leaves affected with tar spot will destroy the overwintering stage of the fungus. Leaf Rust.—In Illinois, willow is affected occasionally by two fungi which cause leaf rust. One fungus, Melampsora bige- lowti, has larch for its alternate host and the other fungus, M. abieti-capraearum, has fir for its alternate host. Leaf rust caused by either fungus produces golden yellow to orange, powdery pus- tules on the lower surfaces of leaves during the summer. By late summer and autumn, these pustules become dark brown or black. They may be scattered or so closely crowded that the entire lower surface of an affected leaf appears powdery. Leaf rust on willow usually causes insufficient damage to warrant treatment for its control. CARTER: ILLINOIS TREES: THEIR DISEASES 99 Cytospora Canker.—This stem disease, caused by the fungus Cytospora chrysosperma, produces cankers on branches and trunks of willow similar to the cankers described on poplar. The treatment given for the control of this disease on poplar is effec- tive on willow. Species of willow resistant to this disease should be used when available. Black willow and peach willow are re- ported as resistant to Cytospora canker. Crown Gall.—This stem disease, caused by the bacterium Agrobacterium tumefaciens, produces swellings or warty, tumor- like galls on many species of trees and shrubs, fig. 24. On most trees the galls are confined mainly to the bases of the trunks or the roots. However, on willow and poplar the galls may appear on the branches also. Severely affected trees are retarded in growth, and affected roots and branches may die. Crown gall usually causes very little noticeable damage on large trees, but it has been known to kill young trees. Young trees affected with galls should be destroyed. Affected branches on large trees should be removed. In nursery plantings where crown gall occurs, all diseased stock should be destroyed. Wounding of stems and roots of healthy plants should be avoided, since infection occurs through wounds. Susceptible stock should not be planted in soil infested with the crown gall organism. TREES RELATIVELY FREE OF DISEASE Many native and naturalized trees in Illinois are relatively free of diseases. Some of these trees grow large and are used for shade as well as for ornamental purposes. Others grow as large shrubs or small trees and are used mostly for ornamental pur- poses. The group of large trees includes ailanthus, bald cypress, beech, black locust, ginkgo, hackberry, hickory, honey locust, Kentucky coffee tree, larch, magnolia, mulberry, Osage orange, sweet gum, tulip tree, tupelo, and walnut. The group of small trees includes dogwood, hop hornbeam (ironwood), hornbeam (blue beech), pawpaw, persimmon, plum, sassafras, shadbush (serviceberry), and water elm. Some of these trees, as walnut, are subject to frequent attacks by insects, and some have habits of growth or other characteristics that make them undesirable in some situations. Some Publications of the Wu1INois NaruraL History SURVEY BULLETIN Volume 26, Article 4.—Efhciency and Selec- tivity of Commercial Fishing Devices Used on the Mississippi River. By William C. Starrett and Paul G. Barnickol. July, 1955. 42 pp., frontis., 17 figs., bibliog. Volume 26, Article 5.—Hill Prairies of IIli- nois. By Robert A. Evers. August, 1955. 80 pp., frontis., 28 figs., bibliog. Volume 26, Article 6—Fusarium Disease of Gladiolus: Its Causal Agent. By Junius L. Forsberg. September, 1955. 57 pp., frontis., 22 figs., bibliog. Volume 27, Article 1.—Ecological Life History of the Warmouth. By R. Weldon Larimore. August, 1957. 84 pp., color frontis., 27 figs., bibliog. Volume 27, Article 2.—A Century of Biological Research. By Harlow B. Mills, George C. Decker, Herbert H. Ross, J. Cedric Carter, George W. Bennett, Thomas G. Scott, James S. Ayars, Ruth R. Warrick, and Bessie B. East. December, 1958. 150 pp., 2 frontis., illus., bibliog. $1.00. Volume 27, Article 3.—Lead Poisoning as a Mortality Factor in Waterfowl Populations. By Frank C. Bellrose. May, 1959. 54 pp., frontis., 9 figs., bibliog. 50 cents. Volume 27, Article 4.—Food Habits of Migra- tory Ducks in Illinois. By Harry G. Ander- son. August, 1959. 56 pp., frontis., 18 figs., bibliog. 50 cents. Volume 27, Article 5—Hook-and-Line Catch in Fertilized and Unfertilized Ponds. By Donald F. Hansen, George W. Bennett, Robert J. Webb, and John M. Lewis. August, 1960. 46 pp., frontis., 11 figs., bibliog. 25 cents. CIRCULAR 48.—Diseases of Wheat, Oats, Barley, and Rye. By G. H. Boewe. June, 1960. 159 pp., frontis., 56 figs. Single copies free to Illinois resi- dents; 25 cents to others. BIOLOGICAL NOTES 33.—A New Technique in Control of the House Fly. By Willis N. Bruce. December, 1953, 8 pp., 5 figs. 34.—White-Tailed Deer Populations in Illi- By Lysle R. Pietsch. June, 1954. 24 nois. pp., 17 figs., bibliog. 35.—An Evaluation of the Red Fox. By Thomas G. Scott. July, 1955. (Second printing.) 16 pp., illus., bibliog. 36.—A Spectacular Waterfowl Migration Through Central North America. By Frank C. Bellrose. April, 1957. 24 pp., 9 figs, bibliog. 37.—Continuous Mass Rearing of the Euro- pean Corn Borer in the Laboratory. By, Paul Surany. May, 1957. 12 pp., 7 figs, bibliog. ‘ 38.—Ectoparasites of the Cottontail Rabbit in Lee County, Northern Illinois. By Lewis Ji Stannard, Jr., and Lysle R. Pietsch. June, 1958. 20 pp., 14 figs., bibliog. { 39.—A Guide to Aging of Pheasant Embryos. By Ronald F. Labisky and James FP¥ Opsahl September, 1958. 4 pp., illus., bibliog. 40.—Night-Lighting: A Technique for Cap turing Birds and Mammals. By Ronald F_ Labisky. July, 1959. 12 pp., 8 figs., bibliog 41—Hawks and Owls: Population Trend From Illinois Christmas Counts. By Richar( R. Graber and Jack S. Golden. March, 196¢ 24 pp., 24 figs., bibliog. a 42.—Winter Foods of the Bobwhite in Souther) b Illinois. By Edward J. Larimer. May, 196( 36 pp., 11 figs., bibliog. MANUAL 3.—Fieldbook of Native Illinois Shrubs. B Leo R. Tehon. December, 1942. 307 pp 4 color pls., 72 figs., glossary, index. $1.7! 4.—Fieldbook of Illinois Mammals. By Donal F. Hoffmeister and Carl O. Mohr. Juni 1957. 233 pp., color frontis., 119 figs., glo: sary, bibliog., index. $1.75. List of available publications mailed on request. Single copies of ILt1Nois NATURAL HisTory SuRVEY publications for which no price is liste will be furnished free of charge to individuals until the supply becomes low, More than one copy of any free publication may be obtaine educational institutions and official organizations within the State of Illinoi nominal charge may be made. without cost by after which prices to others on quantity orders of these publications will be quoted upon request. Address orders and correspondence to the Chief, TLLINOIS NATURAL History Survey, Natural Resources Building, Urbana, Illinois Payment in the form of money Springfield, order or check Illinois, must accompany requests for those publications on which a price is Ss! made out to State Treasurer of Illino | A 4 , : . _: | iP i it} . % i¢ Lt Pe pa a ake