Borers that feed under the bark of trunks and branches are one of the most serious problems of peaches both in commercial orchards and home fruit plantings. These borers also attack cultivated plums, cherries, nectarines, and apricots, and wild cherries and plums. There are two species of borers: the peachtree borer (Synanthedon exitiosa), which is sometimes referred to as the greater peachtree borer, and the lesser peachtree borer (Synanthedon pictipes). The peachtree borer is common in young nonbearing trees or in unmanaged plantings, while the lesser peachtree borer is common in large managed orchards. See Extension factsheet, HYG-2032-94 for information on peachtree borer. In this fact sheet, information that distinguishes lesser peachtree borer from peachtree borer is italicized.
The lesser peachtree borer infests the upper parts of the trunk and scaffold branches and is most troublesome on injured or weak trees. Borers feed on the growing inner bark of trees, and tunnel between the inner bark and the sapwood. The bark eventually peels off of damaged areas. Damage weakens the tree and predisposes it to attack by other pests and diseases. A gummy mass mixed with sawdust is usually found on the outer bark at the place where a borer started an attack. Entries are often found where there are cankers or wounds caused by other factors such as pruning or winter injury.
The adult borers are moths that looks more like wasps than moths. The male of lesser peachtree borer has a body that is blue-black, marked with narrow yellow bands on the abdomen, thorax, head, and legs; its front wings and hind wings are clear but the edges and veins are outlined with blue-black scales. The male is 15 to 23 mm long, its wings have a slight yellow tinge, and it usually has only two narrow bands of yellow visible on the abdomen. The female lesser peachtree borer is very similar to the male except for features of the antennae and tip of the abdomen.
Eggs are small, oval, reddish brown, and hard. The larva is dull white with a brown head and three pairs of short jointed legs. Larvae are 0.6 mm (1/32 inch) when first hatched, and 23 mm (7/8 inch) when fully grown.
Empty pupal case (A) and cocoon under bark (B).(from Grote and Robinson, 1917, OH Agric. Experiment Station Bull. 307) Lesser peachtree borer: adult female.
Lesser peachtree borer usually has two generations per year in Ohio, with adult emergence in May and June, then again in August and September. In some years they may have only one generation. The lesser peachtree borer overwinters as an inactive larva under the bark. The larva resumes feeding and completes its larval stages in the spring. When fully grown, the larva pupates under the bark then emerges as a new adult. The adult is the only stage that leaves the tree. Soon after emerging, the female moth lays her eggs under bark scales or on rough bark. Each female lays about 400 eggs. Eggs hatch in eight to ten days into larvae that bore into the tree.
While pruning in early spring, growers should look for symptoms of borer activity on the scaffold branches. If symptoms are found, then a more intensive control strategy is needed than if symptoms are not found.
In order to determine the most appropriate time to apply insecticide, a sticky trap or bucket trap baited with a pheromone lure can be used to monitor activity of lesser peachtree borer in the adult stage. Pheromones are synthetic products that mimic the natural sex attractant emitted by female moths in order to attract mates. Only male moths are attracted to pheromone traps. Traps for lesser peachtree borer should be hung 4 to 5 feet above ground and set up in late April. It is important to notice when emergence begins (when the first moth is trapped) and when emergence reaches a peak (when the number of moths trapped per week is highest). At peak emergence, there may be about 75 lesser peachtree borer moths per trap per week.
The pheromone lure for lesser peachtree borer attracts lesser peachtree borer and should repel the peachtree borer, but sometimes nontarget species also get caught in traps. Trapped moths thus should be examined carefully to be sure the correct species is being counted. If you have a trap for peachtree borer as well as a trap for lesser peachtree borer, the two traps should be separated by at least 60 feet (20 meters) to minimize trapping of nontarget species.
Natural Control Several wasp species are known to parasitize eggs or larvae of lesser peachtree borer. Ants, spiders, and lacewings prey on larvae in exposed locations, and birds feed on larvae and adults. These natural enemies are not capable of adequately controlling borers.
Cultural Control Avoid improper pruning, mowing, fertilizing, or harvesting operations that injure bark and thus attract borers. Any cultural practices that promote healthy trees will also make borer attacks less likely. Trees should be trained so that branches form wide angles rather than narrow angles.
Mechanical Control In small plantings, borers can be effectively controlled by killing larvae mechanically. In the spring at the time buds are bursting, insert a knife or wire into holes that indicate where borers are located, with the intention of smashing the larvae. This can also be done in late fall.
Behavioral Control Mating disruption is the name of a new strategy that will soon be marketed for borer control. Small dispensers filled with lesser peachtree borer pheromone are attached to all trees in the orchard, and they cause the atmosphere throughout the area to be filled with the scent of the borer's sex attractant. Male moths are then unable to locate female moths, mating is prevented, and no fertile eggs are laid. This strategy is effective only in large (>5 acre) plantings.
Chemical control is preventive when insecticide is applied to trees before borer eggs hatch, so that small borer larvae contact a toxic residue as they crawl into trees. Control may also be achieved by fumigant action of the insecticide, which can kill larvae already in trees at the time of application. An insecticide with long residual action gives the best control of borers. Thorough coverage is necessary. Insecticide should be applied as a bark drench to the trunk and scaffold branches at a rate of at least one-half to one gallon of spray mix per tree.
The best time to treat and the number of insecticide applications needed for lesser peachtree borer control depend on whether trees are known to be infested with this pest.
In orchards where trees show little or no sign of infestation by lesser peachtree borer, one treatment is adequate; it should be applied at the time that the second adult flight is peaking, usually in early September, usually as a post-harvest application.
In orchards where trees do show signs of infestation by lesser peachtree borer, then an earlier application is needed to target the first generation in June, as well as the early-September application that targets the second generation. The first treatment should be applied 10 days after adults begin to emerge, which will probably be in mid-May.
Lindane or multipurpose orchard pesticide may be used, and some brands of chlorpyrifos (Dursban), endosulfan, and carbaryl (Sevin) are labelled for borer control in home peach plantings. Insecticide should be applied to the bark by a paint brush or a hand sprayer.
Insecticide cover sprays applied by conventional air-blast sprayers will help suppress light infestations of lesser peachtree borer, but a bark drench with a high-volume, low-pressure handgun is required for good control. Chlorpyrifos (Lorsban 4E) or endosulfan (Thiodan 3EC or Thiodan 50WP) may be used. One application of chlorpyrifos is effective for about 12 weeks; one application of endosulfan is effective for about six weeks. Lorsban must be applied to the bark and must not be applied to the fruit; it may be applied only once per year on peaches and nectarines or three times per year on cherries, and it may not be used within 14 days of peach or nectarine harvest or within six days of cherry harvest. Thiodan may be used two times per year and it may touch the fruit. Thiodan should not be used within 21 days of cherry harvest or seven days of plum harvest; for peaches, nectarines, and apricots, the pre-harvest restriction is 21 days if used only on the bark or 30 days if used on the fruit.
This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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