658 YEARBOOK OF AGRICULTURE 1953 destructive on quince. Its native host plants include hawthorn, Amelanchier, and wild . It also infects the fruit of some varieties of . The fungus is G. clavipes. The three fungi were studied early in the nineteenth century. At first the forms on the cedar and on the apple Rust Diseases were considered to be different. By 1886, however, more study showed that the spores produced by the fungus on cedar of Apple trees would infect apples and that the spores produced on apples were re- sponsible for new infections on the ce- D, H, Palmiter dar. The rust diseases cannot spread from cedar to cedar nor from apple to Many a fruit-growing district in the apple but must alternate between the East is "a land of red apples and red two hosts. cedars.'' In the Midwest where cedars The fungus that causes cedar-apple did not occur naturally the pioneers rust spends almost 2 years of its life often planted them for windbreaks cycle on the cedar trees. Gedar leaves near orchards. The combination would are infected between July and April be felicitous were it not that some fungi by aeciospores blowm from lesions that require both apples and cedars for develop on apple leaves. Small brown their development. galls, called cedar apples, appear dur- Before our cultivated apples, quince, ing the sumxner but do not mature until and other pome fruits w^ere introduced the following spring, when they may from Europe, three such fungi, natives, be 2 inches in diameter. After a few infected the leaves or fruit of native warm spring rains, about the time crab apples, hawthorn, serviceberry, apple blossoms are in the pink stage, and sorbus, all members of the rose the galls increase in size and extrude family. They could not overwinter on gelatinous tendrils from round de- those hosts, how^ever, and used the ce- pressions on all sides of the galls. The dar trees Juniperus virginianae, J. scopu- tendrils—long, thin, and bright or- ¿orum, J, horizontalis^ and J. communis as ange—form a mass several times that winter hosts. of the original brown galls. The ten- Since three different fungi are re- drils, or horns, consist of many two- sponsible for three different rust dis- celled teliospores, which germinate in eases of apples, we must know some- the tendrils by producing four sporidia thing of their life history and symptoms from each of the two cells. All telio- on both apple and cedar before w^e can spores do not germinate at the same control them. time. With each rain the horns push The best known of the three diseases out farther and expose more spores. is cedar-apple rust. It produces yellow When the supply of teliospores is ex- lesions on the leaves and fruit of wild hausted the galls dry up and may drop. and cultivated apples and is caused by If the twigs bearing the galls are killed, the fungus Gymnosporangium juniper i vir^ the dead galls often remain hanging ginianae, on the cedars through the next year. A similar disease is hawthorn rust. After the small sporidia are pro- Its common native host is hawthorn. duced, a decrease in humidity causes It also infests apple leaves but not the them to be discharged forcibly into the fruit. It is caused by the fungus G. air. Air currents carry them consider- globosum. able distances. Viable spores have been The third disease is quince rust. It is collected by airplane traps several RUST DISEASES OF APPLE 659 miles from redcedars at altitudes up irregular in shape than the apple rust to one-half mile. They may eventually galls. The teliospores are extruded as settle on apple leaves or fruit. If a film dark-orange, wedge-shaped protru- of moisture is present and the temper- sions during spring rains. Sporidia may ature is between 56° and 61° F., the be discharged for 2 or 3 days while sporidia germinate quickly and pene- the galls are drying. Unlike the apple trate the host tissue in i to 3 hours. rust galls, they persist and produce Little germination occurs at tempera- spores again another year. tures below 47° or above 85°. Either The hawthorn rust fungus does not leaf surface may be infected. Fruit le- cause lesions on apple fruit. The lesions sions are usually near the blossom end. on the upper surface of apple leaves The yellow rust spots appear on the are similar to those of the apple rust upper surface of the apple leaves in i fungus but smaller. On the lower leaf to 3 weeks, depending on the tempera- surface, the two fungi look quite dif- ture and the susceptibility of the ferent. With the hawthorn rust the variety. As the spots increase in size, a aecia are relatively few in number and sticky exúdate containing pycniospores are at the center of the lesion and sur- appears. The true function of this rounded by a region of orange-col- spore stage was not known until 1933, ored leaf tissue. The peridial tubes, in when investigations by J. G. Liu at which the spores are formed, are per- the University of Wisconsin showed sistent and long and spread apart to that insects are attracted by this ex- release the aeciospores. They do not údate. They carry spores from one curl back, as do those of the apple rust spot to another and thus fertilize rust fungus. the fungus. Thus it continues growth The aeciospores of the hawthorn rust and completes its life cycle on the are mature in the fall. The wind dis- apple tree by producing the final spore tributes them. They do not germinate stage. well until cold weather approaches. After fertilization, the fungus grows Some spores perhaps do not germinate through the leaf and produces fruiting until the following spring, when new bodies, called aecia, on the lower sur- galls on the cedars are started. If no face of the leaf. Fruit of susceptible apple orchards are nearby or if or- apple varieties also may be infected chards are well sprayed, aeciospores and spores may be produced. Aecio- from infected hawthorn trees may spores are produced in thin-walled serve to reinfect the cedars. tubes. In July and August the spores mature and are released by the split- THE QUINCE RUST fungus infects ting of the tube walls. They are carried twigs, branches, or trunks of the cedar, about by the wind. Those that land on but not the leaves. It produces elon- cedar leaves may germinate at once to gated, swollen, rough cankers, which start galls or may remain dormant turn red as the teliospores begin to until the following spring, when they form in the spring. Jellylike masses of germinate to infect the new growth. yellowish-orange teliospores later are Now that better control methods are exuded during the spring rains about available, few spores are produced on the time apple trees are in bloom. orchard trees. Infection of cedar trees The cankers remain active and in- is largely from spores produced on wild crease in size year after year unless the or seedling apple trees growing near twig or branch dies. Spore forms are the cedars. like (but larger than) those of the other apple rust fungi. Infections of THE LIFE HISTORY of the hawthorn apple leaves result in flecks or abortive rust fungus is about the same as that lesions. The fruit of many apple of the cedar-apple rust fungus. The varieties may be infected, but few if galls produced on cedar trees are more any aecia are produced on most 66o YEARBOOK OF AGRICULTURE 1953 varieties. The fungus sporulatcs abun- county. Complaints of severe damage dantly on quince and hawthorn fruits from rust diseases w^ere also reported and twigs, however. They are covered from Iowa, Wisconsin, and New York. by a mass of bright-orange tubes, in Another serious outbreak occurred in which the spores are formed. The 1927 and 1928. Considerable loss of spores formed on infected quince or fruit occurred in New York and Iowa. hawthorn fruit are then able to Rust diseases injure apples in several reinfect cedar trees. ways. The infected fruit is reduced in Many of the apples infected by grade, so that most of them are culls. quince rust drop in June. Those that Quince rust tends to cause a high mature are misshapen and may have proportion of Mclntosh fruit to drop dark-green sunken lesions, usually in June, and fruit of and some near the blossom end. Some varieties, other varieties tends to crack. Con- such as Cortland, tend to crack open. siderable loss from secondary rots may Infection becomes visible 2 or 3 weeks follow rust infection. Fruit size is after bloom, and the lesions often reduced by heavy foliage infection, so appear as dark-green raised areas near that even uninfected fruits have little the blossoxTi end. As the fruit grows, the value. Infected trees are greatly weak- diseased parts develop slowly and ened by defoliation and the reduction finally appear as sunken areas. The of active leaf surface. As few as 10 rust tissue under the sunken area is hard spots on a leaf may cause leaves of some and extends to the apple core. varieties to fall by midsummer. Such trees may suffer winter injury and MOST OF THE APPLE plantings in the often fail to set fruit buds for the United States before 1850 were seed- following season. Young trees in ling trees. No two of them were alike. nursery and orchard may die because If disease or insects were unusually of infection and defoliation. harmful to a particular tree, it was considered a weakling and removed or METHODS OF CONTROLLING the dis- left to its fate. Trees later were eases were considered even before fun- propagated by grafting, and named gicidal sprays were commonly used. varieties were selected for quality of The fact that apple trees can only be their fruit. It soon became evident infected by the spores produced on that certain varieties w^ere subject to cedars suggested the possibility of con- leaf and fruit infections of the rust. trol by removing the cedars—a simple During that period, about a century and practical procedure in places ago, , Rome Beauty, Winter where cedars were not too numerous Banana, Salome, , and York and belonged to the fruit grower. Imperial apples became popular as the This method of control was first re- apple industry expanded rapidly in ported in 1892 following experiments the Eastern and Central States, But by L. R. Jones. Investigations of the those very varieties were highly suscep- effectiveness and cost of removing tible to cedar-apple rust—it is not cedars were made by H. S. Reed and surprising that trouble developed wher- C. H. Crabill in Virginia between 191 o ever they were planted near cedar and 1915. As other methods were less trees or cedar trees were planted effective or more expensive at that near them. time, the removal of cedars became In 1912 the loss in Virginia from the commonly recommended control rust on apples was estimated to be practice. Eight States—Virginia, Ar- more than 500,000 dollars. Besides, kansas, Kansas, Nebraska, West Vir- many trees were greatly weakened and ginia, Pennsylvania, New York, and young trees were killed before they Missouri—passed laws empowering reached bearing age. West Virginia authorities to remove cedars. reported a loss of 75,000 dollars in one In the East, however, many orchards RUST DISEASES OF APPLE 661 were in valleys fringed by cedar- ommended then for and bearing hills on which it was imprac- other diseases. Bordeaux gave good tical to exterminate the cedar. The control of rust when several properly esthetic value of cedars in some estates timed applications were made, but and parks outweighed the value of that was expensive and often caused nearby orchards. severe injury to the fruit and leaves, Another method of avoiding rust lay especially when frequent applications in the differences in the susceptibility were made early in the season. of different trees to rust. But varieties Liquid lime-sulfur, introduced as a reported resistant in one place were fruit fungicide in 1907, was tried on said to be susceptible in another. apples in many States. It gave only We now know that the cause of that partial control unless frequent appli- early confusion was lack of under- cations were made. Inadequate spray standing that three different fungi equipment was no doubt a factor. were responsible for the rust. Paul R. Many spray schedules called for appli- Miller, of the Department of Agricul- cations at 2-week intervals; more fre- ture, pointed out in 1939 that varieties quent applications were considered like Rome Beauty and Wealthy were to be impractical. Because lime-sulfur susceptible to all three rust fungi; proved to be a good scab fungicide, varieties like York, Grimes, , however, and caused less injury than and Jonathan were susceptible to apple bordeaux on certain varieties, it soon and hawthorn rusts but were resistant replaced or supplemented bordeaux in to quince rust; and many districts. and Delicious were infected only by Wettable sulfur products, tested ex- quince rust. D. E. Bliss in Iowa in 1933 tensively following the rust epidemics discovered that strains of the fungi of 1927 and 1928, were found to be exist—the strains may limit or extend commercially feasible in New York the list of varieties usually considered when they were applied on a 5-day susceptible to a given species. schedule or timed to precede rainy The early lack of understanding of periods during and following the the problem meant that progess in the bloom. But despite all the experimen- selection and breeding of apples for tal work on fungicides up to 1940, resistance to rust was slow. Now such growers often failed to get good re- work is going ahead full speed. Vari- sults. The removal of cedar trees near eties resistant to all species of rust may susceptible varieties was still consid- be produced some day. We already ered the best method of controlling rust have some varieties resistant enough to diseases in most States. be grown commercially in places where Of the many fungicides developed more susceptible kinds would suffer between 1940 and 1953 only ferbam severe damage without special appli- has been outstanding for the control cations of fungicides. of all three forms of rust on apples. But changing varieties of apples to It is available for spray purposes as avoid disease is indeed a slow process. a 76-percent active, dry, wettable Orchards already planted cannot be powder. changed without great expense even if The use of ferbam makes unnecessary resistant varieties are available. New the close timing of applications that varieties must be acceptable to proc- are necessary when sulfur is used to essors and consumers of the fresh fruit control rust, because ferric dimethyl before extensive orchard plantings can dithiocarbamate, the active part of be recommended. ferbam, is translocated externally and The use of fungicides to control the internally to such an extent that new diseases was stimulated by the out- growth is protected. J. M. Hamilton, breaks of rust early in this century. L. O. Weaver, and I, working at the Bordeaux mixture was generally rec- New York State Agricultural Experi- 662 YEARBOOK OF AGRICULTURE 1953 ment Station, found that the toxic ele- mentally in combination with the ment in Fermate (ferbam) is taken into phenyl mercury fungicides and with the plant in sufficient amounts to give captan fungicides to control both a degree of protection through systemic rust and scab. action, particularly against the cedar- rust fungus. Consequently even a spot- IF YOU GROVS^ cedar trees as orna- ty coverage of ferbam controlled rust, mentals, it is well to protect them whereas a spotty coverage of sulfur from rust—to keep the rust fungi from failed to control. Ferbam applied to the disfiguring them and to keep the fungi lower leaf surface prevented infection from producing spores that would when the rust spores were placed on infect flowering apples or other orna- the upper leaf surface. mental plants susceptible to rust. Ferbam (76-percent active) used If you plan to make new plantings alone at the rate of i or 1.5 pounds to of cedars, it is wise to consider using 100 gallons of spray at the pink, petal- the cultivated varieties of cedar that fall, and lo-day stages of apple de- are resistant to the rust. For twenty velopment gave satisfactory control of years Anthony Berg selected, propa- the rust diseases in New York over a 10- gated, and tested redcedar trees for year period. When a combination of resistance to cedar-apple rust. In 1941 wettable sulfur and ferbam was used he published his results with a selec- for control of both scab and rust, one- tion from West Virginia that showed half the usual amount of each fungi- outstanding resistance. cide was used, and an extra application In established plantings you can get during bloom was made. Because the partial control by spraying the sur- number and timing of sprays for rust rounding apple or other susceptible control may vary in different sections pome trees with ferbam. That will of the country, owners of apple trees restrict greatly the source of new in- should follow the recommendations is- fection. Commercial orchards sprayed sued by their own county agents or with ferbam produce few rust spores State experiment stations. capable of infecting cedars. Many of The use of 4-percent ferbam dust the cedar infections now come from with sulfur as the diluent, applied be- spores produced on neglected apple fore or during rainy periods, has satis- trees which, as likely as not, can be factorily controlled apple rust diseases. removed. Such dusts can be applied quickly. The direct spraying of cedars with Commercial growers like them partic- bordeaux and sulfur for rust control is ularly when special applications are done sometimes. The usual procedure needed, especially during the bloom is to make one application in July or period. Ferbam dusts applied by plane August to give protection from spores have also given good control. that are discharged in the summer. So far no other fungicides (except Another application in late fall or maybe some other carbamates) have early spring will kill any spores that equaled ferbam against rust diseases, may remain on the cedars until spring. but many commercial orchardists for Such sprays are said to give 80 to 90 whom rust is not a serious problem percent control. use other fungicides, such as wettable Spring applications of sulfur, bor- sulfur, naphthoquinones, and gly- deaux, and dinitrocresylate have been oxalidines. Additional rust protection used on rust-infected cedars to prevent has been obtained by adding one-half the cedar galls from producing viable pound of ferbam to each 100 gallons spores. Rush P. Marshall reported in of spray when those materials are used 1941 the results of tests conducted in during the period of critical rust Connecticut in which one early spring infection. application of bordeaux 180 (a com- Ferbam has also been used experi- bination of copper sulfate, lime, SOOTY BLOTCH AND FLY SPECK 663 monocalciuxn arsenite, zinc arsenite, and fish oil) gave superior control ojf spore formation and greatly reduced the number of new rust galls on cedar trees.

THUS THREE METHODS of controlling the fungi that cause apple, quince, and hawthorn rusts are available. Sooty Blotch In localities where either the cedar or the pomaccous host can be elimi- nated the remaining host will be and Fly Speck unharmed. Resistant varieties of both host plants are available and are recom- A. B. Groves mended if both plants are to be used in the same area. Sooty blotch and fly speck are For most commercial apple or- the common names for two diseases of chards, nurseries, and estates where the apple that can mar the appearance wild cedar trees are abundant, how- of the fruit. ever, the use of ferbam in sprays or Sooty blotch appears as sootlike dusts is the most practical means of spots or blotches. Fly speck makes dark control. spots that look somewhat like fly Susceptible cedars may also be pro- specks. Although the two diseases are tected by one or tw^o applications of not caused by the same fungus (sooty bordeaux 180 in places where it is blotch is caused by Gloeodes pomigena desirable to prevent damage to the and fly speck by Leptothyrium pomi), cedars or to reduce the production of they are so commonly found in spores that would otherwise reinfect association and develop freely under pomes. the same favorable climatic conditions that they are usually described to- D. H. PALMITER has been associated gether. with the New Tork State Agricultural Ex- Sooty blotch is also widely known by periment Station siîîce igß^. He is a the name cloud and less commonly as graduate of Oregon State College and re- sooty smudge, sooty spot, and inky ceived his doctorate in plant pathology at the spot. It appears as dark-brown to University of Wisconsin. In Mew Tork he olive-green spots or smudges on the has investigated methods of controlling surface of mature pomaceous fruits. various fruit tree diseases by means of Fly speck appears as well-defined, fungicide applications. slightly raised, small, dark spots on the surface. The specks commonly occur in Anthony Berg: A Rust-resistant Red Cedar, groups, seldom singly. The two dis- Phytopathology, volume jo, pages Sy6~8y8, 1940. eases cause little or no actual injury to N. J. Giddings and Anthony Berg: Apple Rust, West Virginia University Agricultural Ex- the fruit, but by disfiguring it they periment Station Bulletin /j^, pages /—75, ^9^5- lower its market value. They are most L. R. Jones: Apple Rust and Cedar Apples, troublesome in orchards on low land or Vermont Agricultural Experiment Station Annual in other places where air drainage is Report Number 6, page 83, i8g2. Paul R. Miller: Pathogenicity, Symptoms, poor and the humidity tends to remain and the Causative Fungi of Three Apple high. Both diseases are easily con- Rusts Compared, Phytopathology, volume sg, trolled, but the possibility of their pages 801-811, I939' occurrence cannot be ignored if D. H. Palmiter: Three Rust Diseases of Ap- ples and Fungicide Treatments for Their blemish-free fruit is to be produced. Control, Neu) Tork State Agricultural Experiment Sooty blotch occurs throughout the Station Bulletin y^6, pages 1-26, 1952. humid fruit-producing regions of