Brown rot is the most important disease affecting all stone fruit (peaches, nectarines, plums, and sweet and sour cherries). However, other diseases such as peach leaf curl, Cytospora canker, plum black knot and cherry leaf spot also should be considered. Borers, catfacing insects (plant bugs, stink bugs) and the oriental fruit moth are usually the most destructive among insect pests that attack peaches. The peachtree borer also attacks other stone fruit trees. The plum curculio can destroy an entire plum crop and is harmful to other stonefruits, as well.
Cultural and Mechanical Practices for Disease and Insect Control Sanitation Measures
Cytospora canker. Delay pruning any stone fruit trees until March or April. Be alert for any evidence of Cytospora cankers. These cankers are dark, sunken areas on limbs and shoots with gum protruding through the bark, often with a raised callus margin. The canker pathogen often enters major limbs through old wounds, broken limbs and weak shoots that are killed by low winter temperatures. Therefore, pruning thin, willowy water sprouts in the center of the tree during the late summer (early August) helps prevent the establishment of cankers within the main tree structure. Small cankers on shoots and limb tips should be removed completely during the pruning operation; little can be done once the cankers grow larger or become established in the crotch or on the trunk. Do not use commercial wound paints on pruning cuts. Make cuts so that only the small, raised branch collar remains on the supporting branch, and allow them to heal naturally. Limb damage that occurs during the growing season should be repaired immediately; never wait for the dormant season.
Black knot of plum. On plums, in addition to Cytospora cankers, look for symptoms of black knot disease at the time of pruning. These are rough, black tumors or overgrowths that develop on shoots and limbs. They should be pruned out completely. Remove the knots from the orchard and destroy them. If possible, remove wild plums and wild cherries near the planting.
Cherry leaf spot. The cherry leaf spot fungus overwinters on old dead leaves on the ground. Rake the area under the tree thoroughly and destroy all old leaves to control cherry leaf spot disease. Do this in the fall as soon as leaves drop or in the early spring, before bloom. This procedure can be very effective for small plantings isolated from other cherries.
Oriental fruit moth. The first symptom of infestation by oriental fruit moth is wilting shoot tips. As soon as wilting tips are noticed, prune the shoots and destroy them to prevent the larvae from reaching maturity.
Plum curculio. Promptly collect and destroy any fruits that fall prematurely.
Yellowjackets, bees and wasps. Plan on harvesting stone fruit over a period of one to two weeks. Regularly pick fully ripened fruits, and remove any that have fallen or any of those showing decay. This discourages the buildup of yellowjacket, bee and wasp populations around and in your trees so that special insecticide treatments are not necessary.
Traps for oriental fruit moth.
Oriental fruit moth can not be controlled by traps, but the oriental fruit moth population can be monitored by traps so that the best time for an insecticide spray can be determined. The trap uses a sex pheromone lure that attracts only male oriental fruit moths. The lure should be placed in a sticky cardboard trap or a bucket-style trap. The trap should be set up at bloom (Table 13). A rough rule for the best time to spray to control the first generation is about 6 days after the catch of moths in the trap reaches a peak; this is usually around the time of the first cover spray. A rough rule for the best time to spray to control the second and third generations is about 3 days after the moth catch reaches a peak. A more refined rule is to calculate degree days (base 45F) after sustained trap catch begins for each generation, and spray after 200 degree days have accumulated and spray again after another 200 degree days. Each day, the number of degree days is the average temperature minus the base temperature. For a base of 45F, daily degree days = [(maximum temperature + minimum temperature) / 2 ] - 45.
Special Problems on Stone Fruit Peachtree Borers
The peachtree borer works beneath the bark at or near the ground level; it is primarily a pest of young peach trees but populations can build up and cause the decline and death of older trees. The lesser peachtree borer is a similar pest that attacks trees at wounds anywhere in the lower few feet of the trunk and scaffold limbs rather than at ground level. The presence of borers is indicated by masses of gum that contain small brown particles of bark at the base of the tree, or the occurrence of frass and empty pupal cases protruding from tree wounds. Adults (moths) of peachtree borer begin emerging in early June in southern Ohio, and late June in northern Ohio. Adults of lesser peachtree borer begin emerging about one month earlier than peachtree borer, and the lesser peachtree borer has a second generation in late summer.
Avoid mechanical injuries to the trunk and limbs, which attract borers. If evidence of borers is found, borers can be killed mechanically using a knife or flexible wire to puncture the larvae through the bark where fresh frass is found. It is important to prevent peachtree borer damage by protecting the base or trunk of the tree with an insecticide. New trees can be dipped in insecticide solution before planting. Insecticide solutions are effective when applied with a paint brush to the affected area on the trunk. The best time to apply a trunk treatment is at the time of peak emergence of adult peachtree borer, which is usually in early August.
Mites
Where spider mites are a problem, the best control strategy is to use several tactics. First, a thorough spray of horticultural oil at green tip will reduce the overwintering population. Second, use insecticides only when most needed, to encourage survival of natural enemy insects that feed on mites. Third, select insecticides that have at least some mite activity, such as diazinon, malathion, or rotenone. Finally, use insecticidal soap either alone or mixed with any insecticides to be applied for control of pest insects.