The ABC's of Greater Peachtree Borer

For the latest control information, go to http://utahpests.usu.edu/

This information is from that web site.

Growers in the Wasatch Front region should begin treatment next week on peach, nectarine, and apricot. (Cherries and plums are rarely attacked in Utah.)

Greater peachtree borer (sometimes called trunk, root, or crown borer) is a day-flying moth that resembles wasps. You may see them (thin, metallic blue-black body with clear wings) resting on leaves. Adults lay eggs on the lower 12" of the tree trunk or on nearby soil, and larvae bore their way into the wood and remain there for the next 9-11 months.

Sprays only need to be applied to the lower 12-18" of trunk and any exposed roots. The residual material of the insecticide on the bark will kill the eggs and newly hatching larvae.

The greater peachtree borer (Order Lepidoptera, Family Sesiidae) is native to North America where wild cherries and plums are its native hosts. It is a sporadic pest in Utah stone fruit orchards, but if left unmanaged it can be severe enough to cause tree loss.

The adults are clearwing moths. The larvae are pinkish-white caterpillars that bore into the trunks where they feed just under the bark in the cambial tissue. There is one generation per year, but some larvae may require 2 years to complete development.

Extensive larval feeding can girdle and kill trees. The larvae primarily attack tree trunks just at or below the soil line, but may enter trunks up to 12 inches above the ground. Other tree problems that are confused with peachtree borer injury include winter freeze and mechanical injury, and infection by canker-causing fungi such as Cytospora. All of these problems can cause copious sap or gum to exude from holes or cracks in the bark. Key symptoms of peachtree borer infestation are the presence of sawdust and frass mixed with the gummy exudate near the base of the trunk.

Prevention is the most effective approach to management. Pheromone-based mating disruption and trunk sprays with synthetic insecticides are the primary management tactics. Adult peachtree borers become active in mid to late June in northern Utah and trunks should be protected from tunneling larvae beginning the first week of July (3-4 weeks earlier in southern Utah) through late August to early September.

Adult - Monitoring Stage • Color and Appearance: Similar in appearance to wasps with a metallic-blue body and clear wings; however, the female's forewings are covered with blue scales. The female has a distinct orange band on the abdomen (Fig. 1); the male has three or four narrow, yellow-white abdominal stripes. • Size: Female is about 1 inch long, and male is slightly smaller, with a narrower abdomen.

When: Moths begin flying in early summer, approximately mid June through early September. They are active during the day, especially between 10 a.m. and 2 p.m. • Mating occurs immediately after emergence; females can lay eggs within 30 minutes of mating and each female can lay 200-1200 eggs over her 6-7 day life-span; the majority of eggs are laid in days 1-3. Egg • Size and Shape: Approximately 0.03 inch long, oval, and hard. • Color: Reddish brown. • Where: Female lays eggs on the lower tree trunk under bark scales, on rough bark, or on nearby soil. • Hatch occurs in 7-10 days.

Larva - Damaging Stage • Size and Color: Newly hatched larva is approx. 0.06 inch long; fully grown larva is up to 1.25 inches long; pinkish-white with a brown head (Fig. 2). • Where: Larva bores through the bark immediately upon hatching and feeds on inner bark and cambium of the tree, forming galleries. • Feeds under the bark all summer, and moves down to the base of the tree to overwinter. • Resumes feeding in the spring when soil temperature reaches 50º F; causes the most damage at this time; pupates in May to August.

Larva - Overwintering Stage • Size and Color: Can overwinter as 1st to 4th instars; larva size depends on what stage it is in when overwintering begins; pinkish-white with brown head. • Where: Overwinters under the bark at the base of the tree, usually below ground level.

Pupa • Size and Color: 0.75 inch long; light brown; held within a cocoon made of silk, gum, and chewed wood fragments. • Where: Pupate in the top layer of soil, within a few inches of the host tree, or in the tree near the bark surface. • When: In the late spring through summer. • 2 to 4 week development period depending on temperature; soil moisture encourages emergence. • Pupal skin is left at the base of the tree or in the soil after the adults emerge.

Greater peachtree borer larvae attack only the lower 12 inches of the host trunk, and usually enter at or just below ground level. Larvae will occasionally feed in larger roots near the soil surface. Larvae tunnel between the inner bark and sapwood in the cambium, and can girdle and kill young trees in one season. Older trees may withstand the damage, but will be predisposed to attack by other insects and diseases, and can be killed after several years of infestation.

Visual symptoms include loose, dead bark and masses of gummy sap mixed with frass exuding from entry and exit holes. Leaves on a portion of the tree may turn yellow and wilt, and the tree canopy will eventually die back. Similar-looking gummy deposits on the upper trunk or limbs are likely caused by winter or mechanical injury or fungal pathogens, and do not indicate infestation by peachtree borer. The presence of peachtree borer can be confirmed by the skins of pupae left attached to the bark of the lower trunk or in the soil near the trunk base, or by a larva and/or larval tunnel under the bark.

Look for injury symptoms when pruning trees in the spring and early summer. If symptoms are found, a more intensive control program is needed. Determine the timing of first adult emergence with pheromone traps. Monitoring adults with traps throughout the summer in stone fruit orchards will provide information on the occurrence and severity of the insect.

Protection of host trees from peachtree borer is the most critical during the first 3 to 5 years after planting. There are few registered insecticides with adequate longevity to protect trunks from egg-laying and hatching larvae. Mating disruption is the recommended control for commercial stone fruit orchards. For orchards less than 1 acre, or for home yard trees, preventive trunk sprays is the primary control.

Apply insecticides as a bark drench at a rate of 1/2 to 1 gallon of spray mix per tree. Thoroughly cover the lower 12 inches of trunk and soak the ground at the base of the tree. Do not allow the sprays to contact fruit. Remove prunings, debris, or weeds at the base of trees to avoid interference with spray coverage.

Cultural and Mechanical Controls • Select appropriate fruit tree species for the site to avoid stressed and unhealthy trees. • Use good cultural practices (i.e., fertilization, irrigation, etc.) to maintain trees in a healthy and vigorous state. • Paint trunks with a 1:1 dilution of white latex paint to water, or apply white tree wraps in the winter to prevent bark damage from sunscald. • Do not leave wraps on trees during the summer. This has been shown to increase borer attack. • Avoid mechanical and rodent-caused injuries to trunks. • Certain rootstocks have been found to result in fewer emerging adults. ‘Siberian C' peach rootstock had 40% fewer emerging adults than ‘Lovell' rootstock in one study. • Larvae inside trunks can be killed by inserting a wire into entry holes. Kill larvae in the late summer and fall before they spend the winter and inflict their most extensive feeding damage the following spring. • Keep the base of trees free of vegetation. Heat and dryness reduce the survival of eggs and larvae.

Written by: Larry A. Sagers Extension Horticultural Specialist Utah State University Thanksgiving Point Office