Extension Bulletin E-1439, January 1981, FILE COOPERATIVE EXTENSION SERVICE MICHIGAN STATE UNIVERSITY

Transcription

1 Extension Bulletin E-1439, January 1981, FILE COOPERATIVE EXTENSION SERVICE MICHIGAN STATE UNIVERSITY

2 by Adele M. Childress Department of Botany and Plant Pathology This bulletin should aid the homeowner in identifying diseases most ommonly found in home orhards. Disease desriptions and photographs are limited to those symptoms the home orhardist is most likely to enounter. A listing of the diseases inluded in the bulletin and their relative importane is given in Table 1. Proper orhard maintenane praties (pruning, fertilization, et.] are always essential to the suess of disease ontrol programs. Cultural ontrols are suggested in the text onsult with your loal ounty extension agent for updated hemial ontrols. No one hemial an ontrol all diseases, but some are available in ombinations to inrease the range of disease protetion while reduing the number of appliations. These multipurpose sprays are available at most nursery and garden supply stores. Chemials must be handled with extreme aution; be sure to follow diretions arefully for storage, handling and rates of appliation. Apple Sab Sab is the most ommon disease of apples; it must be ontrolled annually if high quality fruit is desired. The sab fungus auses brown to blak velvety spots or lesions on leaves and fruits (Fig. 1, 2). On leaves, spots develop on either side but are more onspiuous on the upper surfae. TABLE 1. Relative Importane of the Tree Fruit Diseases Found in the Home Orhard. Disease Problems Apple Sab Cedar-apple Rust Powdery Mildew Sooty Bloth and Flyspek Sooty Mold Fire Blight Pear Sab Brown Rot Peah Leaf Curl Peah Sab Blak Knot Cherry Leaf Spot Apple v v TREE FRUIT CROP Peah & Sour & Nee- Plum & Sweef Pear tarine Prune Cherry v v v v v v v = very ommon disease requiring annual ontrol measures = ommon disease but often limited to ertain varieties or restrited to ertain loalities. Annual ontrol measures required where the disease is a problem. Leaf yellowing followed by defoliation may our where sab is not ontrolled. Large sab spots may distort and rak apple fruits. The sab fungus overwinters in apple leaves on the ground. Spores (seeds] of the fungus are released from overwintered leaves about the time apple buds begin to open in spring. Infetion to leaves and fruit may our during wetting periods from rains of nine or more hours depending on temperature. Fig. 1. Apple sab on leaves and fruit. Cover photos: (ounter lokwise, top left to right): apple sab infetion of alyx end of fruit, Stanley prune infeted with brown rot fungus; blak knot on limb of plum; edar-apple rust gall on edar.

3 Fig. 2. Apple sab developing on underside of leaves. Fig. 3. Cedar-apple rust gall on red edar. To ontrol sab, remove leaves and fruit on the ground every fall. Sab resistant varieties suh as Prima, Prisilla, Sir Prize, Liberty, and MaFree are ideal for the home orhard beause they eliminate the need for a sab fungiide spray program. However, these varieties will need spraying for inset and mite ontrol. To ontrol sab on suseptible varieties, a series of fungiide sprays must be applied to protet the developing foliage and fruit. Two or three sprays will not ontrol sab. Apply fungiides on a 7- to 10-day shedule beginning at the green tip stage in April and ontinue through early June. In June, July, and early August, use a 14-day shedule. Seven to ten sprays will be required eah season for good results. Fungiides will not harm honeybees and may be applied during bloom. Insetiides do harm honeybees and should not be ombined with fungiides during bloom. Cedar-Apple Rust Cedar-apple rust infets both apple and red edar trees. Infetion to edar is neesary for the fungus to survive from season to season. On edar, the fungus produes brown to reddish-brown galls that are inonspiuous until spring, when warm moist onditions ause long, orange, gelatinous horns to protrude from the galls (Fig. 3). On apple, small, pale yellow spots develop on the upper leaf surfae shortly after bloom. These spots enlarge to about one-quarter inh, beome bright orange, and ontain small blak Fig. 4. Apple leaves and fruit with edar apple rust (ourtesy, J. D. Moore, U. of Wisonsin.) speks (fungal fruiting bodies) in their enter (Fig. 4). Lesions on young fruit may ause dwarfing and distortions. Resistant apple varieties should be planted sine the destrution of red edars is often not pratial for the homeowner. Suseptible varieties should be sprayed with an effetive fungiide on a 7- to 10-day shedule from the pink stage of bud development to about 30 days after petal fall. Powdery Mildew of Apple Powdery mildew suseptible apple varieties inlude: Jonathan, Rome Beauty, Cortland, Monroe, and Idared.

4 Diseased leaves have a white-to-grayish appearane due to the growth of the mildew fungus over the leaf surfae and may beome distorted and brittle with age. Shoots beome overed with white fungal growth, have a withered appearane, and are often stunted in growth (Fig. 5). The mildew fungus overwinters in dormant buds and infets the leaves and shoots as they emerge in spring. Pruning out severely infeted shoots and spurs is usually adequate for ontrolling powdery mildew in the home orhard, partiularly if mildew suseptible varieties are avoided. If many trees are involved, a fungiide may be applied at 5-7 day intervals from early pink stage to petal fall, then at a day inter- Fig. 5. Powdery mildew infeted apple shoot. val until terminal growth eases. A mildewide may be inorporated into the regular sab ontrol program, or selet a fungiide that ontrols both diseases. Sooty Bloth and Fly Spek Sooty bloth and fly spek usually our together on apple and pear fruits (Fig. 6). These fungi do little damage to the fruit, but the market value (appearane) of the fruit is redued. Sooty bloth develops as olive-green-to-brown irular spots. Several small spots may oalese and over large areas of the fruit. Fly spek appear as groups of 10 to 20 shiny blak dots or speks on the fruit. Both diseases our in the latter part of the growing season. Where sooty bloth and fly spek have been destrutive, apply a fungiide through the summer months to within 30 days of harvest. Periodially utting the grass and weeds so they will not ome in ontat with the fruit will also help ontrol these diseases. Sooty Molds Sooty molds are fungi that grow on the honeylike seretion (honeydew) produed by insets suh as aphids, leafhoppers, and pear psylla. Fruit and leaves affeted by sooty mold beome overed by a blak myelial mat of the fungus.that results in redued yield and vigor of the tree. Problems with sooty mold an be prevented by ontroling the insets that produe the honeydew. Fig. 6. Sooty bloth and fly spek on the surfae of apple (ourtesy, K. D. Hikey, Pennsylvania State U.) Fire Blight of Pear and Apple Fire blight is a baterial disease of pears and apples. The disease kills blossoms, fruiting spurs, terminal growth, and sometimes entire trees. Infeted fruiting spurs and shoots suddenly wilt and turn dark brown or blak (Fig. 7). Often, tips of blighted stems have a rooked appearane. Heavily infeted trees take on a sorhed, "fireblight" appearane (Fig. 8). During warm, humid weather droplets of a stiky ooze may exude from diseased tissues. Infeted fruit develop a brown-to-blak deay, then shrivel into dark, leathery, mummies that persist on the trees.

5 Fig. 7. Diebak of fruit spurs from fire blight. Fig. 8. Fire blight on apple, note severe diebak of spurs and shoots. The bateria live over the winter in infeted wood (ankers) and ooze from raks in the bark in the spring and early summer. Insets and splashing rains arry the bateria from ankers to sites of infetion. To ontrol fire blight, prune out infeted spurs, shoots, and branhes inhes below the infetion during the winter months. If growth has started, disinfet all pruning tools between eah ut with a 10% Chlorox solution. If possible, selet less suseptible varieties for the home orhard. All ommon pear varieties are suseptible. Suseptible apple varieties to avoid inlude: Yellow Transparent, Jonathan, Idared, Fenton (Beaon), and Paulared. Relatively safe varieties inlude Golden Deliious, Deliious, and Mlntosh. Where the disease is serious or the trees are quite valuable, onsider using a spray program with antibiotis. The blossom stage is the most effetive time to spray, and several appliations at this time may be neessary to prevent disease establishment. Pear Sab Pear sab is most notieable on the fruit. Initially, sab lesions appear as velvety, lightgreen spots whih beome blak with age. As the fruit enlarge, the spots may inrease to the size of a quarter; they often distort and rak the pear. Greenish-blak spots may also develop on the lower leaf surfae and on young twigs (Fig. 9). Pear sab overwinters in infeted twigs and fallen leaves. Spores (seeds) of the fungus are produed in the spring starting at the green tip Fig. 9. Pear sab on fruit and leaves. stage of bud development. Rain and several hours of leaf wetness are required for infetion to our. To ontrol pear sab in the home garden: 1) avoid highly suseptible pear varieties suh as Flemish Beauty, Winter Nelis, Sekel, and Anjou; 2) plant and prune trees so they have good air irulation and are not rowded by other trees; and 3) remove the fallen leaves in late fall. If the disease beomes serious, a series of fungiide sprays should be applied during late April at green tip and ontinued through till petal fall. Additional sprays may be neessary during seasons with heavy infetion periods. Brown Rot Brown rot of apriots, herries, netarines, peahes, plums and prunes is a ommon and

6 destrutive disease in the home orhard. It is primarily a disease of mature fruit, although immature fruit and blossoms may beome diseased under ertain onditions. The first symptom of disease is the development of a small, irular, light brown area of deay on the surfae of the fruit (Fig. 10, 11). Diseased areas expand rapidly, often enompassing fruits in one or two days. Under humid onditions, ash-gray tufts of fungal growth develop along the surfae of the deayed area. The presene of these fungal masses helps distinguish brown rot from other disease problems. Rotted fruit may fall to the ground or dry up like a mummy and persist in the tree. To ontrol brown rot, fungiide sprays are needed every 4 to 6 days during bloom and weekly beginning 3 to 4 weeks before harvest. Fungiide sprays are needed partiularly during periods of warm, wet, humid weather. Removing fruits, mummies, and blighted twigs from trees and the ground after harvest makes ontrol easier. Good ontrol of insets that injure the fruit also helps to ontrol this disease. Peah Leaf Curl This disease is a ommon problem on peah and netarines. Symptoms of leaf url appear about the time the shuks fall from the fruits that have set. Leaf url is first reognized by a pukering and urling of the leaves (Fig. 12). Infeted leaves are thikened and often flushed with red or purple. In dry weather, the leaves die and drop off. Young shoots and fruit may also beome infeted. The swollen tissues often have a grayish appearane from spores of the peah-leaf url fungus developing along the surfae. Leaf url an be ontrolled by a single fungiidal spray applied in autumn after leaf fall or in the spring before bud break. Sprays applied after bud break are generally ineffetive. Peah Sab This disease ours on apriots, netarines and peahes. Infeted fruit exhibit small irular, dark green to olive spots (Fig. 13). These spots may oalese to over large areas on the Fig. 10. Brown rot on peah fruit. Fig. 11. Deay of sweet herries from brown rot. Similar symptoms are produed on prunes and sour herries. fruits. Severely infeted fruit are redued in size and may have raked or withered skin. A series of fungiide sprays may be applied beginning days after the petal fall stage of bud devlopment to 40 days before harvest. Sprays for brown rot may help redue peah sab infetion. Blak Knot of Plum and Prune Blak knot ours on both wild and ultivated plums and prunes. It auses elongated swellings or knots on twigs, saffold limbs, and sometimes the trunk (Fig. 14). The knots are usually 6-12 inhes in length but only 2 or 3 inhes wide. Young knots are greenish and soft but beome blak and hard with age.

7 Fig. 12. Peah leaf url. To ontrol blak knot, remove infeted twigs and branhes in late fall or early spring (by Marh 15). Cut the branhes off about six inhes below the base of the knot. Also, remove severely infeted trees and wild seedlings in the viinity of the home orhard. Sanitation measures usually ontrol the disease adequately, but may be supplemented with a fungiide program if the disease is unusually diffiult to ontrol. The most effetive times to spray are green tip, bloom, petal fall, and shuk fall. Additional sprays until terminal growth stops may be neessary under severe onditions. Cherry Leaf Spot Cherry leaf spot is a disease of tart and sweet herries and some prune varieties. It is more ommon in orhards than on isolated trees in the bakyard. Infeted leaves turn yellow and fall off (Fig. 15). When examined losely, small (about 1/8 inh in diameter), irular, purple spots are visible on the upper leaf surfae and light pink to white masses are visible in the enter of the Fig. 13. Sab on peah fruit. Fig. 14. Blak knot on branhes of prune. Fig. 15. Tart herry tree defoliated from leaf spot.

8 Fig. 16. Tart herry leaves with leaf spot. spots, on the lower leaf surfae (Fig. 16). Often the enter of the spots will fall out giving the leaf a "shot-hole" appearane. Control measures inlude removing infeted leaves from around the trees in autumn or early spring. Fungiide sprays may be applied, starting at petal fall or when the first leaves have unfolded, 10 days after petal fall, 24 days after petal fall and the last soon after harvest. Appreiation is expressed to A. L. Jones for assistane in preparing this publiation and for use of his olor slides and of olor separations from North Central Regionai Extension Publiation No. 45 "Diseases of Tree Fruits". The help of Frank Laemmlen, Mihigan State University, Paul C. Peknoid, Purdue University, and T. J. Burr, New York State Agriultural Experiment Station, in reviewing the text of this publiation is aknowledged. MICHIGAN STATE UNIVERSITY MSU is an Affirmative Ation/Equal Opportunity Institution. Cooperative Extension Servie programs are open to all without regard to rae, olor, national origin, or sex. Issued in furtherane of ooperative extension work in agriulture and home eonomis, ats of May 8, and June 30,1914, in ooperation with the U.S. Department of Agriulture. Gordon E. Guyer, Diretor, Cooperative Extension Servie, Mihigan State University, E. Lansing, Ml This information is for eduational purposes only. Referene to ommerial produts or trade names does not imply en- I C O O P E R A T I V E dorsement by the Cooperative Extension Servie or bias against those not mentioned. This bulletin beomes publi proppytpmq (~)M erty upon publiation and may be reprinted verbatim as a separate or within another publiation with redit to MSU. ^ ^ LlNOIV-'lN Reprinting annot be used to endorse or advertise a ommerial produt or ompany. I SERVICE 1P-15M-1:81-V.P., Prie 50