Browse by title articles:

Peachtree Borer

by Celeste Welty    

Borers that feed under the bark of peach trees are one of the most serious pest problems in commercial peach orchards and in home peach plantings. 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 fact sheet, HYG-2033-94 for information on the lesser peachtree borer. In this fact sheet, information that distinguishes peachtree borer from lesser peachtree borer is italicized.

Damage

The peachtree borer attacks healthy bark near the soil line, usually just below the ground line or in the lower 30 cm (12 inches) of the trunk. (Fig.1.) Borers can kill young trees when trunks are girdled by feeding. 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 winter injury.

Figure 1. Peachtree borer larva (1), cocoon (2), empty pupal case (3), and cocoon with pupa emerging (4). (from Gossard & King, 1918, Ohio Agric. Experiment Station Bulletin 329)

Appearance

The adult peachtree borers are moths that looks more like wasps than moths. The adult female peachtree borer has a distinctive appearance; she has a dark blue-black body with an orange band on the abdomen, dark blue front wings, and clear hind wings. The adult male is blue-black, marked with narrow yellow bands on the abdomen, thorax, head, and legs; front wings and hind wings are clear but the edges and veins are outlined with blue-black scales. The male is 18 to 33 mm long, the transparent portions of his wings are strongly tinged with yellow, and at least 3 to 4 narrow bands of yellow are usually visible on 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 1.5 mm (1/16 inch) when first hatched, and 30 mm (5/4 inch) when fully grown.

Figure 2. Peachtree borer adult female (A), adult male (B), fully grown larva (C), female pupa (D), male pupa (E), and cocoon with pupa skin protruding (F).

Life Cycle

Peachtree borer has only one generation per year. It overwinters as an inactive larva under the bark, and resumes feeding and completes its larval stages in spring and early summer. When fully grown, the larva pupates under bark or in the soil near the tree base, then emerges as a new adult. The adult is the only stage that leaves the tree.

In central Ohio, peachtree borer adults start to emerge in mid-June; emergence peaks in midsummer and extends into September. Emergence is greater on days after a rain. Soon after adults emerge, the female moths lay 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.

Monitoring

While pruning in early spring, growers should look for symptoms of peachtree borer activity at the base of the tree. 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 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 peachtree borer should be hung three feet from the ground and set up in late May. 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 50 peachtree borer moths per trap per week.

The pheromone lure for peachtree borer attracts peachtree borer, as it should, but unfortunately it can also attract the lesser peachtree borer and other common species such as the lilac-ash borer. Trapped moths thus should be examined carefully to be sure the correct species is being counted. If a trap for lesser peachtree borer is set up in the same planting as a trap for peachtree borer, the two traps should be separated by at least 20 meters (60 feet) to minimize trapping of nontarget species.

Non-Chemical Control

Natural Control 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.

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 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

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 peachtree borer. Protection from peachtree borer is most critical during the first three to five years after planting. When new trees are planted, the roots and crowns should be dipped in insecticide before planting; this will protect them from borers during their first year. In established plantings, insecticide should be applied as a bark drench at a rate of one-half to one gallon of spray mix per tree. Thorough coverage is necessary. The insecticide should run down the trunk and soak the ground at the base of the tree. Any prunings, debris, or weeds at the base of trees should be removed so that they do not block the treatment.

Timing

The best time to treat and the number of insecticide applications needed for peachtree borer control depend on whether trees are known to be infested with this pest. One insecticide treatment is adequate in orchards where trees show little or no sign of peachtree borer infestation; the best time to treat is at the time of peak adult flight, which is usually in early August. In orchards where borer injury is found on most trees, two treatments should be made: the first about 10 days after adults begin to emerge (late June) and the second at peak emergence about six weeks later (early August). If trees are infested by both peachtree borer and lesser peachtree borer, then insecticide application should be delayed until early September.

Insecticides in Home Fruit Plantings

Lindane or multipurpose orchard pesticide may be used, and some brands of chlorpyrifos (Dursban), endosulfan, and carbaryl (Sevin) are labelled for this use in home plantings. Insecticide should be applied to the bark by a paint brush or a hand sprayer.

Insecticides in Commercial Orchards

Insecticide cover sprays applied by conventional air-blast sprayers will do little to control peachtree borer; a bark drench with a high-volume, low-pressure handgun is required for good borer 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.

Traditional Remedy

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.


-----------------

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-1868