Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. * + ae 8 eo Tie) ld Jee a £ yf Se A. ary A es bd 8 “a > = ° st on a ; Ad 3, U.S. DEPARTMENT OF AGRICULTURE. -__- BUREAU OF PLANT INDUSTRY—BULLETIN NO. 144, B. T. GALLOWAY, Chief of Bureau. Jy . 7 >= b ™ ? FAPPLE BLOTCH. SERIOUS DISEASE OF SOUTHERN ORCHARDS. W. M. SCOTT, Patrnotrocisr, AND 3 etaae 5 AMES B. RORER, Assistant PATHOLOGIST, Be Fruir Disease INVESTIGATIONS. . “et ‘. - = > 3 RA IssuED MARCH 6, 1909. ’ : Ls * a ZA ot aS bot Boh a x - Rx a = ae Wo < = 2 Tees Pad == =e - ~ —) —* =) = WASHINGTON: GOVERNMENT PRINTING OFFICE. ; 1909. PLATE |. Bul. 144, Bureau of Plant Industry, U. S. Dept. of Agriculture. AHoen& Co Baltrmore. APPLE BLOTCH ON FRUITS, TWIGS, AND LEAF. U.S. DEPARTMENT OF AGRICULTURE. BUREAU OF PLANT INDUSTRY—BULLETIN NO. 144. B. T. GALLOWAY, Chief of Bureau. Agree, BLOTCH, ~A SERIOUS DISEASE OF SOUTHERN ORCHARDS. BY W. M. SCOTT, Partuotoatsr, AND JAMES B. RORER, Assistanr Parnovoerst, Fruit DIsEASE INVESTIGATIONS. ISSUED Marcu 6, 1909. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1909. , BUREAU OF PLANT INDUSTRY. Physiologist and Pathologist, and Chief of Bureau, Beverly T. Galloway. Physiologist and Pathologist, and Assistant Chief of Bureau, Albert ¥. Woods. Laboratory of Plant Pathology, Erwin F. Smith, Pathologist in Charge. Fruit Disease Investigations, Merton B. Waite, Pathologist in Charge. Investigations in Forest Pathology, Haven Metcalf, Pathologist in Charge. Cotton and Truck Diseases and Plant Disease Survey, William A. Orton, Pathologist in Charge. Pathological Collections and Inspection Work, Yiora W. Patterson, Mycologist in Charge. Plant Life History Investigations, Walter T. Swingle, Physiologist in Charge. Cotton Breeding Investigations, Archibald D. Shamel and Daniel N. Shoemaker, Physiolo- — gists in Charge. Tobacco Investigations, Archibald D. Shamel, Wightman W. Garner, and Ernest H. Mathewson, in Charge. : Corn Investigations, Charles P. Hartley, Physiologist in Charge. Alkali and Drought Resistant Plant Breeding Investigations, Thomas H. Kearney, Physi- ologist in Charge. Soil Bacteriology and Water Purification Investigations, Karl F. Kellerman, Physiologist . in Charge. Bionomic Investigations of Trepical and Subtropical Plants, Orator F. Cook, Bionomist in Charge. Drug and Poisonous Plant and Tea Culture Investigations, Rodney H. True, Physiologist in Charge. : Physical Laboratory, Lyman J. Briggs, Physicist in Charge. Agricultural Technology, Nathan A. Cobb, Crop Technologist in Charge. Taxonomic and Range Investiggtions, Frederick V. Coville, Botanist in Charge. Farm Management, William J. Spillman, Agriculturist in Charge. . Grain Investigations, Mark Alfred Carleton, Cerealist in Charge. Arlington Experimental Farm and Horticultural Investigations, Lee C. Corbett, Horticul- turist in Charge. Vegetable Testing Gardens, William W. Tracy, sr., Superintendent. Sugar-Beet Investigations, Charles O. Townsend, Pathologist in Charge. Western Agricultural Extension, Carl S. Scofield, Agriculturist in Charge. Dry-Land Agriculture Investigations, E. Channing Chilcott, Agriculturist in Charge. Pomological Collections, Gustavus B. Brackett, Pomologist in Charge. Field Investigations in Pomology, William A. Taylor and G. Harold Powell, Pomologists in Charge. Experimental Gardens and Grounds, Edward M. Byrnes, Superintendent. Foreign Seed and Plant Introduction, David Fairchild, Agricultural Explorer in Charge. Forage Crop Investigations, Charles V. Piper, Agrostologist in Charge. Seed Laboratory, Edgar Brown. Botanist in Charge. Grain Standardization, John D. Shanahan, Crop Technologist in Charge. Subtropical Garden, Miami, Fla., P. J. Wester, in Charge. Plant Introduction Garden, Chico, Cal., W. W. Tracy, jr., Assistant Botanist in Charge. South Texas Garden, Brownsville, Tex., Edward C. Green, Pomologist in Charge. Farmers’ Cooperative Demonstration Work, Seaman A. Knapp, Special Agent in Charge. Seed Distribution (Directed by Chief of Bureau), Lisle Morrison, Assistant in General Charge. i ee i aren aS ayo tt a a timc, lic hata Editor, J. ©. Rockwell. Chief Clerk, James E. Jones. FRUIT DISEASE INVESTIGATIONS. * SCIENTIFIC STAFF. M. B. Waite, Pathologist in Charge. C. L. Shear, Pathologist in Charge of Small Fruit Disease Investigations. W.M. Scott, Pathologist in Charge of Orchard Spraying Experiments and Demonstrations. James B. Rorer, Assistant Pathologist. P. J. O'Gara, G. F. Miles, W. A. Ballard, Lon A. Hawkins, Mrs. Anna K. Wood, T. W. Ayres, Clara H. Hasse, and F. V. Rand, Scientific Assistants. F. W. Faurot, Special Agent. 144 Withdrawn 2 FEB7 240 i be | K i= lye iN th : LETTER OF TRANSMITTAL. U. S. DrepartTMENT oF AGRICULTURE, Bureau or Puant Inpustry, OrrFIcE oF CHIEF oF BuREAU, Washington, D. C., November 25, 1908. Str: I have the honor to transmit herewith a paper entitled “Apple Blotch, a Serious Disease of Southern Orchards,” by Messrs. W. M. Scott, Pathologist, and James B. Rorer, Assistant Pathologist, of this Bureau, and recommend its publication as Bulletin No. 144 of the special series of the Bureau of Plant Industry. This paper contains the first full account of the apple blotch, which has recently come into prominence as one of the most serious diseases of the southern portion of the apple belt. The life history of the fungus causing the disease has been worked out and the source of the annual infection determined. It has been conclusively shown by the spraying experiments and demonstrations carried on by the Bureau for the past three years in - the Ozarks that the disease can be successfully controlled at a nom- inal cost, and the results of this work are reported in this paper. The writers wish to acknowledge their indebtedness to the members of the Benton County (Ark.) Horticultural Society for their hearty _. cooperation in connection with the field work reported upon in this paper. Respectfully, B. T. Gattoway, Chief of Bureau. . Hon. James WIrson, Secretary of Agriculture. 9 144 a Cea N WS. ELE ST ee eee ee ee ee ee Peecnowonand Dekavior of apple blotch)... 2... 2-. 22252. ccee-. sec. nese Sener ed etre eta ane, Ra tene A064) ot koe tol cn kee sees nets s Sis eee es ee a eee Ae et ke ES us corn, {oe fee Pee ee ae ae er SO eR Ae hs See OSES ah. CODES ESSE PRES OU AR a Sg rs ay ee ae gee ee Sees Pe PEN M SELOMCR Nyt 18a Ses bei = ee Soe hse Sain osee nce ESE Ce Pe eRe ae ee ee Eue history of the funous.. 352.22... 2 SE le Re, Deeb ee. aa ee «RUN TEN EEN Gs NEA Ey SET She sO aaa IU, Gael aa aa ie a a Inoculation experiments ......-.-.---- 2 eae alg ne i een ope et PER PIO GE UNGR Pte a” isins hs oe Sool oe i oe ee ee eee Speagie cx Pecinemsanmentonville, Ark: 22. 222.6202 ones t see lee Silvie cxperunents ub Aaravetie;, Atks. ..522.-02- 02225-26228 se2+ ee pirencincon bordeaux mixture for apple'blotch -_-..-......-..-..+.---: Eecommendations for the control of apple blotch _.......................-- Combination treatment for apple blotch and other diseases...........------- ESC UGE SS ap a eee a eee Orta eee ater ee eee he een oko nc Sen oases sek See see cw ewes 144 5 Pirate ‘ZT. Oe o08 Iv. V. Wall: [LESTER ATON Ss ; Page. Apple: bloteh om fruits twigs) and leat e222 ses seee seen Frontispiece. Fig. 1.—Orchard of Northwestern Greening apple trees almost destroyed by apple blotch. Fig. 2.—Six Ben Davis apples, show- ing the character of the disease on young fruit.............-..- 26 Microscopic and cultural characters of the apple-blotch fungus. --- 26 Fig. 1.—A Ben Davis apple, showing blotches produced by inocu- lation. Fig. 2.—A Gano apple, showing blotches resulting from natural infection. Fig.3.—A power spraying outfit in operation - 26 Fig. 1.—Crop of Ben Davis apples from a properly sprayed tree. 26 Fig. 2.—Crop of Ben Davis apples from an unsprayed tree-.---- Fig. 1.—Crop of Limbertwig apples from a treesprayed three times, - beginning at the right period. Fig. 2.—Crop of Limbertwig apples from a tree sprayed three times, beginning too late...--- 144 6 al al a bee - i ae. | : B. P. I.—451. APPLE BLOTCH, A SERIOUS DISEASE OF SOUTHERN ORCHARDS. INTRODUCTION. Following the successful treatment of bitter-rot in Virginia in 1905 by the Department of Agriculture, demonstration work for this and other diseases was instituted in the Middle West in the spring of 1906. The demonstrations were primarily intended to show the best methods of controlling the apple scab and bitter-rot, both of which had been reported as very destructive throughout that region in previous years, but as the season progressed it was found that apple blotch was far more destructive than apple scab and bitter- rot combined. The writers, who were in charge of this demonstra- tion work, naturally turned their attention to an investigation of the blotch disease. | The attention of the Department was first called to this disease in 1897, when specimens of it were received from Maryland and Texas. Mr. M. B. Waite photographed the affected fruits and determined the fungus to be a species of Phyllosticta. Since that time specimens of it have been received frequently from various parts of the eastern United States, but in no case was it reported as a serious pest. Upon inquiry, however, it was found that it must have been prevalent to an injurious extent in the Ozarks of Arkansas and Missouri for the past six or seven years. It has been commonly confused with apple scab and the damage done by it attributed to scab, which probably accounts for its serious nature having been overlooked until recently. The disease is well distributed over the eastern half of the United States, having been recorded at the Department of Agriculture from Alabama, Arkansas, Georgia, Illinois, Kansas, Kentucky, Maryland, Michigan, Missouri, Nebraska, New Jersey, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Texas, Vir- ginia, and West Virginia, but it reaches the height of destructiveness - in the southern portion of the Ozark plateau. In northwestern Ar- kansas and portions of southern Missouri 75 per cent of the crop is commonly affected, and the disease is almost as bad in portions of southern Illinois. During September, 1906, the writers visited many of the orchards of Benton County, Ark., and found that fully 50 per cent of the fruit in these orchards was rendered unfit for barreling 66103—Bull. 144—09——2 7 8 APPLE BLOTCH IN SOUTHERN ORCHARDS. by this disease. From these observations it was estimated that the loss to the growers in this county alone amounted to $950,000. The disease was even worse in 1907, and although the crop was lighter the higher price of apples made the loss about the same as in the previous year. In 1908 the loss from the disease was immaterial, owing to the failure of the apple crop; however, the few apples that were pro- duced were as badly affected with the disease as were those in the previous two years. An examination made by one of the writers of orchards at various points in southern Kentucky and in Tennessee, Georgia, and Alabama showed that the disease was very destructive in those localities. Not only was the fruit of susceptible varieties rendered unfit for market, but the trees themselves were badly weakened by the cankers. On account of the disease the growing of several varieties well adapted to the locality has been practically discontinued. In certain sections of Alabama and Georgia the Ben Davis, Red Astrachan, Shockley, and Yates varieties, which formerly did well, have in recent years been almost a complete failure, owing apparently to attacks of this disease. It appears, therefore, that apple blotch is the most destructive disease of the southern half of the apple belt. Occasionally bitter- rot, as in the year 1900, overshadows all other diseases in destructive- ness, but taken year by year apple blotch is more serious. Fortunately the disease is amenable to treatment and can not gain a foothold in well-sprayed orchards. It is not sporadic in its nature and must accumulate on the twigs several years before a serious outbreak on the fruit can occur. The disease as 1t appears on the fruit was first reported in 1902 by Clinton,* who attributed it to an undescribed species of Phyllosticta. In 1903 it was reported by Faurot ® as occurring to a serious extent in. southern Missouri, and in 1906 Crandall,° in connection with his work on liquid versus dust spraying, mentioned a disease which may have been the same thing. Scott and Quaintance,? in 1907, gave a detailed description of the disease on the fruit and the results of its successful control by spraying. Later in the same year Rolfs® pub- lished a description, with recommendations for its treatment. The relation of twig cankers and leaf-spots to the fruit blotch was first reported by the writers? in 1907. Almost simultaneously @Tllinois Agricultural Experiment Station, Bulletin 69, pp. 190-192, plate B, fig. 1, a, b, and e. 5 Missouri State Fruit Experiment Station, Bulletin 6, pp. 7-8. ¢ Tilinois Agricultural Experiment Station, Bulletin 106, pp. 217-218. @U. S. Department of Agriculture, Farmers’ Bulletin 283, pp. 14-18, fig. 2. € Missouri State Fruit Experiment Station, Bulletin 16, p. 5. f Proceedings of the Benton County (Arkansas) Horticultural Society, August 8, 1907. 144 ; r , - FRUIT BLOTCHES. 9 Sheldon * reported observations which had led him to the same con- clusions, and in addition he identified the fungus as Phyllosticta solitaria E. & E. Stevens”? later in the same year recorded the eanker form of the disease from several localities in North Carolina. DESCRIPTION AND BEHAVIOR OF APPLE BLOTCH. Apple blotch occurs on the fruit, branches, and leaves. Although the form on the fruit is by far the most important from an economic standpoint, the twig cankers play an important part in the life cycle of the fungus causing the disease. FRUIT BLOTCHES. The first evidence of the disease on the fruit is a very small, in- conspicuous, light brown blotch which under a hand lens has the appearance of a stellate collection of brown fibers just beneath the epidermis. The blotch, spreading radially, increases in size, attain- ing a* diameter of from one-eighth to three-eighths of an inch, sometimes one-half an inch, and becomes darker in color. The ad- vancing margin is irregular and jagged and has a fringed appear- ance. On very young apples the points of infection occasionally show as small water-soaked areas, and in wet weather there may be a yellowish gummy exudation from the spots. Where the spots are numerous they often coalesce and form large blotches, which may cover half the apple or more. The fungus kills only the superficial cells (the epidermis and outer perenchyma), so that the continued growth of the uninvaded tissues beneath results in a cracking of the diseased areas. The cracks thus formed, though usually about half an inch long, may girdle the fruit and extend to the core. The cracks often intersect, forming a cross. The character of the spots varies somewhat on different varieties. There are all gradations, from those on the Missouri variety, which are quite large, much fringed, and smooth, to those on the Limbertwig, which are small, compact, and often umbonate. An occasional spot somewhat rec- tangular in shape may be decidedly sunken and quite black, with a definite margin. (See PI. I, figs. 1 and 2, and PI. IT, fig. 2.) Within a few days after the spots become visible, black pycnidia begin to develop on the diseased areas. Three or four to many occur on each spot, and they may be scattered promiscuously or grouped on a small blister cracked around the margin. The general effect of the blotches on the fruit is to mar.its appear- ance and render it unfit for packing. Moderately affected ~ fruit, especially if not badly cracked, may be evaporated, but much of it *Science, n. s., 26, No. 658, pp. 183-185, August 9, 1907. > Science, n. s., 26, No. 673, pp. 724-725, November 22, 1907. 144 10 APPLE BLOTCH IN SOUTHERN ORCHARDS. can not be used for this purpose, owing to the difficulty of paring, and is a total loss except where it can be used for vinegar. A large per- centage of the affected fruit drops prematurely, and unless utilized immediately becomes a total loss. TWIG CANKERS. The fungus attacks fruit spurs, twigs, and rapidly growing shoots, producing characteristic cankers. On fruiting branches these cankers are small and rather inconspicuous, being about one-eighth of an inch wide and one-half an inch or more long. (PI. I, fig. 4.) They first appear as small purple or blackish blotches. As they increase in size they become brown in the center, retaining a purple margin, but may finally become gray. The bark soon cracks around the cankers, especially along the lateral edges. On rapidly growing shoots, par- ticularly water sprouts, the cankers have the same general appearance as on fruiting branches, but are much larger, often measuring an inch or more in length and sometimes girdling the stem. (PI. I, fig. 3.) The longitudinal cracks appear not only along the edges but through the cankers, giving them eventually a rough and scurfy appearance. This is especially noticeable on those which are two or three years old. Cankers with spore-bearing pycnidia are first formed on the current year’s growth during the summer and fall. The fungus lives over winter in the canker, and during the following spring extends its growth, enlarging the diseased area, and produces new pycnidia on the advancing margin. This growth may continue for several years, as fresh spores have been found on cankers evidently three or four years old. Frequently, however, the canker is cut off from the healthy tissue by cracks, dries up, and later the wound may heal over. As a rule these cankers do not materially injure the tree, kilhng only a few small branches and water sprouts, but in the case of some varieties they are so numerous and extend so rapidly that they lall the large branches, and even the main limbs as well. A block of 200 Northwestern Greening trees at Lanagan, Mo., has been practi- cally destroyed by this disease. When visited by the writers in the spring of 1907, the fruiting wood, water shoots, and even larger limbs were almost completely covered with cankers, and many of them were girdled, so that the trees presented a very ragged and sickly appearance. (PI. II, fig. 1.) So far as the writers have observed, this is the only case in which trees have been killed by the disease, but frequently Missouri, Limbertwig, and Red Astrachan trees become so badly affected that much of the bearing wood is killed and the trees are materially weakened. , In 1906 Mr. H. W. Gipple, of Bentonville, Ark., called the attention | | of the writers to a disease which often kills a large percentage of 144 LEAF SPOTS. 11 the fruit buds in late summer, especially on Limbertwig, Missouri, and Ben Davis trees, and suggested that possibly the apple-blotch fungus was also responsible for this trouble. An _ investigation showed that both the apple-blotch fungus and the black-rot fungus (Sphaeropsis malorum Peck) were present in the diseased buds. Observations in the orchard and culture work in the laboratory showed that the apple-blotch fungus extended down from diseased leaf petioles into the twigs at the base of the buds, which were soon killed. It was found that Sphaeropsis soon invaded the diseased buds and perhaps assisted.in killing them. This trouble begins to show about midsummer and becomes more. pronounced as the season advances, sometimes injuring the fruit buds of a few varieties to such an extent that the crop the following year is almost a failure. During 1907 a similar diseased condition of Winesap buds was found to be common in Arkansas and Missouri. As this variety is practically immune from the Phyllosticta disease, some doubt was thrown on the conclusion given above. Cultures from these diseased Winesap buds nearly always developed Sphaeropsis malorum, but failed to show the presence of Phyllosticta. It would seem, therefore, that at least in the case of the Winesap the black-rot fungus is capable of killing the buds without the aid of the apple-blotch fungus. However, a further investigation of the cause of this trouble is desirable. LEAF SPOTS. The spots on the leaves caused by the apple-blotch fungus are irreg- war, light brown, yellowish, or whitish, and quite small, measuring one-sixteenth inch or less in diameter. Each spot bears one to several small black pycnidia. These diseased areas are scattered promiscu- ously over the surface of the leaf, and frequently occur on the veins, midrib, and petiole. (PI. I, fig. 5.) They are so minute that several dozen may occur on a leaf without attracting attention and perhaps without material injury, but in severe cases they become conspicuous by their numbers, several hundred frequently occurring on a single leaf. The badly affected leaves may drop prematurely or die and turn brown on the tree. The latter condition results from a girdling of the petiole by the fungus, and often in midsummer such susceptible varieties as the Missouri and Limbertwig show tufts of brown leaves involving half or more of the foliage. This results in a weakening, and in many cases the death, of the fruit buds for the following year’s crop. However, as a leaf-spot disease it is of comparatively minor importance, the common leaf-spot being caused by Sphaeropsis malorum Peck, which produces much larger spots. 144 12 APPLE BLOTCH IN SOUTHERN ORCHARDS. INFECTION PERIODS. The twig cankers in which the apple-blotch fungus passes the win- ter are undoubtedly the chief source of infection. During the warm, moist weather of spring the fungus resumes activity and soon begins to produce spores, which ooze from the pycnidia in enormous quanti- ties. These are readily carried by rain and other agents to the young fruits, twigs, and leaves, producing the first spring outbreak of the disease. According to observations made by the writers in the Ozarks during the past three years, infections begin to take place from four to five weeks after the petals have fallen, and the blotches on the fruit appear about three weeks later. In 1906 the apple petals were off by April 29, and the first spots on the fruit were observed on June 26, two months later, while in 1907 the petals were shed by March 31, a month earher than the previous year, and the first blotches were seen on May 31. Although the most extensive outbreak occurs at this early period, infections continue to take place throughout the season, young spots being commonly found on the fruit up to picking time. As is the case with other fungous diseases, outbreaks of apple blotch are more or less dependent upon weather conditions, although, unlike bitter-rot, it develops in cool as well as in warm weather. Rains or heavy dews are necessary for the germination of the spores and the spread of the fungus from the twigs to the fruit. SUSCEPTIBILITY OF VARIETIES. There is a great range in the susceptibility of different varieties to apple blotch, some being almost immune, while others under the same conditions become badly affected. Of the commercial varieties grown in the Ozarks, the Ben Davis, Missouri, and Limbertwig are most subject to the disease, the entire crop of these, especially in old unsprayed orchards, often being destroyed. The disease is equally bad on other varieties, such as the Northwestern Greening, Smith, and Maiden Blush. On the other hand, the Winesap, Jonathan, York Imperial, and some others, are almost immune. The following is a list of varieties, given in the order of their sus- ceptibility to the attacks of this disease. As this list is based solely upon observations made by the writers during 1906 and 1907, mostly in the Middle West, the arrangement is more or less tentative and will probably have to be changed somewhat when further studies are made: Badly affected—Northwestern Greening, Missouri, Ben Davis, Limbertwig, Red Astrachan, Smith, Maiden Blush, Lawver, Shock- ley, Clayton, Willow, Arkansas Black, and Gano. 144 : LIFE HISTORY OF THE FUNGUS. 13 Moderately affected —Oldenburg, Benoni, Arkansas, Bradford, In- gram, Collins, Minkler, Rambo, and Golden Russet. Slightly or not at all affected—Grimes, Winesap, Jonathan, York Imperial, and Red Reese. In addition to those mentioned in the above lst the writers have observed the blotch in various sections on the following varieties: Sherman, Shannon, Arkansas Pippin, Bough, Baldwin, White Pear- main, Yellow Newtown, Smokehouse, and Northern Spy; also on the wild crab apple (Pirus coronaria) in Pennsylvania. CAUSE OF THE DISEASE. The apple-blotch disease is caused by a fungus belonging to the genus Phyllosticta. Clinton,’ in 1902, after having submitted speci- mens of this fungus to both Ellis and Peck, concluded that it was a new species. However, in 1907 Sheldon @ identified it as Phyllos- ticta solitaria E. & E., which was described in 1895? on leaves of the wild crab apple (Pirus coronaria L.). Sheldon did not examine the type specimens, but found that the spores of the apple-blotch fungus, on the wild crab as well as on the common apple, agreed with Ellis and Everhart’s description. Through the kindness of Dr. W. A. Murrill, assistant director of the New York Botanical Gardens, the writers were able to examine the type collection of Phyllosticta solitaria, and found that the spores were practically identical with those of the apple-blotch fungus (Pl. III, fig. 5) and that the spots on the leaves were of the same character as those described above on the leaves of the common apple. LIFE HISTORY OF THE FUNGUS. In 1906, when the writers first began to study the apple-blotch dis- ease, very little was known of the fungus causing it. It was supposed that this fungus lived over winter in the fruits mummified by the disease and that these mummies furnished the source of infection for the new crop. An examination of a large number of such dis- eased fruits revealed so few spores that they could not be considered an important source of infection. The fungus evidently does live over winter in the mummied fruits and in the spring makes an abor- tive attempt to produce either perithecia or pyenidia, but as yet no ascospores and but few pycnospores have. been obtained from this source. It was necessary, therefore, to look elsewhere for the source of spring infection. SOC: CG. > Ellis and Everhart, Proceedings of Academy of Natural Sciences of Phila- delphia, 1895, p. 480. ‘144 14 APPLE BLOTCH IN SOUTHERN ORCHARDS. In September, 1906, the writers found apple-twig cankers caused by a fungus which appeared to be the same as the apple-blotch fun- ous. The fungus from these twig cankers and that from the spots on the fruit grown in the same kind of medium under the same con- ditions were so similar in all respects that one could not be distin- euished from the other. Moreover, spores from both agreed in color, shape, and size. It seemed evident, therefore, that the two diseases were caused by the same fungus. For like reasons it was suspected that the fungus causing the leaf spots and petiole cankers found asso- ciated with the twig cankers was also the same. (PI. ILI, figs. 2, 3, and 4.) Definite proof of this was obtained by inoculation experi- ments made in the following year. In the spring of 1907 at the time the first fruit infections were taking place spores were found oozing in great quantities from pyenidia on the twig cankers, strongly indicating that these cankers formed the principal source of infection for the first outbreak on the fruit. | Under favorable conditions the spores which are carried from the cankers to the young fruits, twigs, and leaves may germinate in fif- teen hours, giving rise to one or two germ tubes, which soon pene- trate the epidermis and form a much-branched mycelium. In the fruit the growth of the fungus is slow and restricted toa few layers of cells just beneath the skin. The mycelium spreads out from the point of infection in a somewhat stellate manner; the invaded tissues turn brown, producing the characteristic blotches as seen on the sur- face. Ina short time the fungus begins to produce pycnidia, or small receptacles in which spores are borne. . (See Pl. ITI, fig. 1.) These pycnidia develop beneath the epidermis and appear as small, black, raised points. When mature, they rupture the epidermis and emit the spores, which are abjointed from short sporophores, through a small opening called an ostiolum. The spores are ovoid to elliptical ovoid, hyaline, unicellular, and measure 8 to 10 by 5.5 to 6.5 ». They are enveloped in a gelatinous sheath, which is frequently prolonged at the apical end into a thread- like appendage. (See Pl. ITI, fig. 4.) These appendages are as a rule rather inconspicuous, usually difficult to discern on spores from dried material, but readily seen on those that have just reached ma- turity. They vary in length, but are generally about twice as long as the spore. They are apparently of the same nature as the appendages which occur on the conidia of Guignardia vaccinit Shear and G. bidwellu (Ell.) V. & R. as described by Shear. The writers have “U. S. Department of Agriculture, Bureau of Plant Industry, Bulletin 110. p. 15, 1907. 144 a pie CULTURAL CHARACTERS. 15 observed similar appendages on the spores of Phyllosticta minima (B. & C.) E. & E., the fungus which causes the common maple leaf- spot. ‘The pycnospores, which are produced in great abundance on young ereen fruits until nearly midsummer, germinate readily and under favorable conditions may reinfect the fruits, twigs, and leaves. As the fruit approaches maturity spore production ceases, although pyenidia-like bodies continue to be formed. It is possible that this is an attempt on the part of the fungus to produce an ascigerous stage, but an examination of a great quantity of diseased fruits both in the fall and in the following spring has failed to reveal any asci. The conceptacles are filled with irregular cell-like bodies rich in pro- toplasm, which may be abortive asci. The growth of the fungus on the twigs is confined to the bark, where it kills the tissues and forms the cankers previously described. The formation of pycnidia begins soon after the cankers are visible and continues throughout the season as the cankers increase in size. These pyenidia produce spores in great abundance which are similar in all respects to those from the fruit and, like them, as shown by inoculation experiments, may infect fruit and leaves. The fungus is perennial in the cankers, enlarging the diseased areas from year to year. CULTURAL CHARACTERS. The fungus grows well on nearly all ordinary culture media, such as potato, apple, prune, and corn-meal agar, sterilized potato cylin- ders, beans, rice, corn meal, and apple twigs. On agar the vegetative growth is quite characteristic, producing an irregular dark gray mass of mycelium, which in its compact radiating appearance suggests the blotches on the fruit. (PI. IIT, fig. 10.) The fungous growth is very dense but quite restricted. The mycelium is for the most part em- bedded in the agar and is greenish black, but the fungous mass has a grayish appearance on account of tufts of short, hyaline hyphe, which are produced over the surface. On apple wood, rice, and corn meal the growth is more extensive and less compact than on agar. The mycelium is made up of profusely branched, anastimosing, septate, thick-walled hyphz about 2.5 » in diameter. (See Pl. III, fig. 9.) The fungus does not fruit freely on culture media, and so far the writers have been able to secure spore-bearing pycnidia only on ster- ilized apple wood and corn-meal agar. Pyenidia-like bodies are formed in great abundance on all media, but these are for the most part sterile. In apple-wood cultures the fungus generally fruits well, producing little groups of pycnidia rich in spores. 144 16 APPLE BLOTCH IN SOUTHERN ORCHARDS. INOCULATION EXPERIMENTS. To show that the fungus which causes the twig cankers is also the cause of the fruit blotch, a series of cross-inoculations was under- taken during the season of 1907. Owing to the press of other work the writers were unable to devote much time to these experiments, so that the results are not all that could be desired. The first inocu- lations were made on June 26, after the main natural infection period had passed and dry weather had set in. As spores could not be obtained in sufficient quantities from the pure cultures then on hand, fertile pycnidia were carefully picked from thoroughly washed young cankers on the twigs and crushed in sterile water, thus liberating the spores. An examination of drops of this liquid showed that it was rich in spores of the canker fungus, and cultures made from it proved to be free from other fungi, but, as might be expected, were slightly contaminated with bacteria. This fluid, containing spores from young cankers, was applied with an atomizer to the fruit and foliage of a Ben Davis tree in a young orchard just beginning to bear, in which the disease had not yet gained a foothold. The fruit and foliage of another tree in the same orchard were sprayed with sterilized water containing spores obtained in a similar manner from pycnidia on the fruit. A third tree was sprayed with sterile water as a check. Although this experiment was made in a period of dry weather, the effects of the inoculation began to show in about a month. On July 24 numerous small blotches were found on the fruits which had been inoculated with the canker spores, as well as on those inoculated with the fruit-blotch spores. The characteristic spots on leaf blade and petiole were also found on both trees. A careful examination of the check tree, as well as of a number of others in the same orchard, revealed no such blotches or leaf spots. As the season advanced the blotches increased in size, and when the crop was picked on September 3, the following data were obtained : | Tree 1, inoculated with canker spores, gave 34 apples affected with a total of 114 blotches and 52 sound apples. Many of these latter were not inoculated because they were in the top of the tree and could not be reached with the atomizer. (See Pl. IV, figs. 1 and 2.) Tree 2, inoculated with spores from the fruit blotches, gave 14 apples affected with a total of 97 blotches and 4 sound apples. Tree 3, check, gave a total of 59 apples, only one of which was affected, and that with only one blotch. Another adjacent tree bore 61 apples, none of which were affected. No cankers were found on the twigs of either inoculated tree, owing perhaps to the hardened condition of the bark brought about by the 144 ee as lo ee ia tea a alt ad nT oy vee ee oie SPRAYING EXPERIMENTS AT BENTONVILLE, ARK. wi dry weather. However, the writers have not yet determined the con- ditions necessary for twig infection. PREVENTIVE MEASURES. The experiments and demonstrations conducted by the writers in 1906 show that the apple-blotch disease may be controlled by proper applications of Bordeaux mixture,’ and these results were confirmed by similar work in 1907. In order to determine the number of appli- cations required and the time at which they should be made the fol- lowing experiments were carried out at Bentonville and Gravette, Ark. : SPRAYING EXPERIMENTS AT BENTONVILLE, ARK. In the orchard of Mrs. Sneed, at Bentonville, a block of eighteen- year-old Ben Davis trees which were badly affected with the disease the previous year and which are said to have never been sprayed before was divided into seven plots of six trees each and sprayed with Bor- deaux mixture. Twelve trees were selected as checks and left un- treated. The crop, including windfalls, from three trees in each plot and from six check trees was sorted with reference to blotch into diseased and sound fruit and the apples in each class counted. The treatment given and the results from each plot are presented in Table I. TABLE I.—Results of experiments for the control of apple blotch on Ben Davis trees, Bentonville, Ark., 1907. Fruit picked September 12 to 19. . Plot numbers (3 trees of each | Treatment with Bordeaux mixture plot). (5-5-50 formula). 5 sere Blotched fruit. Number. | Number. | Per cent. iS a ee ae Reel eee Apr. 27 | May 22| June 15 | July 5 4, 056 208 4.9 eg Ae Oe ee a ee ot ARES 21 May 22.) Sane 15.2.2 .5.22% 3, 008 115 ey Dr eee eee ae eater Perera. t Nane AON eee be 8 || 283 4,999 606 12.5 SP et ee Se See se AS ceases AES eed Nose Sag ssc June 15} July 5 4, 837 595 11.0 Fe ee CEES aE ae ee he eee ee See ae May 22| June 15} July 5 1, 242 2, 705 68.5 ee ee a met ene ee ne ae oe [as —qseeseos June 15| July 5 2,169 4, 237 66.1 (eR ee ee ee Poe ee eae eee eee July 5 1, 403 3, 346 70.5 $,check (6trees), no treatment.|-.--....-.|-.---..--- | BS ee Pee 1,103 10, 235 90.3 In studying this table it should be remembered that the season was a month earlier than normal and that April 27, the date of the first application, corresponds to about May 27 of the previous year, both dates being respectively about a month after the petals had fallen. Moreover, it should be borne in mind that the weather turned dry about the middle of June, after which the rainfall was very light, so “U.S. Department of Agriculture, Farmers’ Bulletin 283, pp. 17-18. 144 18 APPLE BLOTCH IN SOUTHERN ORCHARDS. that but few infections took place during the remainder of the season. The last two applications, made on June 15 and July 5, were there- fore of little value in the control of the disease; but during a season of ordinary rainfall infections take place throughout the season, mak- ing late spraying necessary for proper protection, as was demon- strated in the previous year’s work. The most striking feature of this experiment, as shown in the table, is the effect of the first application, made thirty days after the petals fell. The disease was successfully controlled in all the plots which received this application, while more than half the crop of the plots on which it was omitted was affected. This will be clearly seen by comparing the results from Plots 2 and 5, both of which received three applications, the only difference being that the treatment of the latter was not begun until three weeks after that of the former. The crop of Plot 2 shows only 3.7 per cent of diseased fruit, while 68.5 per cent of that on Plot 5 was affected. Plots 3 and 6 may be simi- larly compared. The crop of the check trees was almost wholly de- stroyed by the disease, 90.3 per cent of the fruit being affected. This, when compared with Plots 1 and 2, in which less than 5 per cént of the crop was diseased, shows very strikingly the good results from timely applications of Bordeaux mixture. (PI. V, figs. 1 and 2.) This experiment was practically duplicated on a block of Limber- twigs in the same orchard, and the results are given in Table II, which follows. TABLE II.—Results of experiments for the control of apple blotch on Limber- twig trees, Bentonville, Ark., 1907. Fruit picked October 5 to 10. Plot numbers (2 trees of each | Treatment with Bordeaux mixture |—*- plot.) (5-5-50 formula). Saini i eae) Blotched fruit. | Number. | Number. | Per cent. Aes ohare Has Ce Serve eeepeicls wesc Apr. 27 | May 22) June 15| July 5 4, 233 360 7.8 Diath Bde deaths = ctselecsinieet eee Sines Apr 21 |e Miaye 22) |i ey Ds eee see 7,170 386 5.1 Dasa aset ie emacs Pe eee eee Apres 27 || Maly: -22)) apace eee 4, 256 305 6.7 ARR Se SoS ule Sat ea SE ee ee Oe eee ANTS) PAT eigen wheat June 15| July 5 6, 824 646 8.6 Eye yore Seca te ata ne Seca te SVs ISLS sn eer May 22) June 15} July 5 3,115 6, 515 67.7 6,check (4 trees), no treatment.|.......... V's eevoreretecsverel| tenia ctsp erat ene reine eee 3, 158 17, 688 | 84.9 The results on the Limbertwig trees, as shown in this table, were about the same as those obtained on the trees of the Ben Davis variety. Again the importance of the first application, April 27, is emphasized, the disease being controlled on all plots receiving this treatment. Plot 2, which received three applications, beginning on April 27, had only 5.1 per cent of the crop affected, while Plot 5, which re- ceived the same number of treatments, though beginning three weeks 144 SPRAYING EXPERIMENTS AT GRAVETTE, ARK. 19 later, had 67.7 per cent of the crop affected. (Pl. VI, figs. 1 and 2.) This emphasizes the fact that in order to control the disease the treat- ment must be given before infections take place. SPRAYING EXPERIMENTS AT GRAVETTE, ARK. At Gravette, Ark., in the orchard of Mr. P. A. Rodgers, a combined experiment and demonstration was conducted. $4. The Seeds of the Bluegrasses. 1905. Price, 5 cents. 86. Agriculture without Irrigation in the Sahara Desert.* 1905. Price, 5 cents. 87. Disease Resistance of Potatoes. 1905. Price, 5 cents. 4, : 88. Weevil-Resisting Adaptations of the Cotton Plant. 1906. Price, 10 cents. 89. Wild Medicinal Plants of the United States, 1906.~ Price, 5 cents. 90. Miscellaneous Papers. 1906. Price, 5 cents. 91. 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