Fruit Insect Focus for August, 1997

Lesser Peachtree Borer, Synanthedon pictipes (Grote & Robinson)

Lesser peachtree borer adultI. Introduction: Lesser peachtree borer (LPTB) is a native insect that was first reported in Pennsylvania in 1868 and is now widely distributed in eastern North America. It is the most important indirect pest of peach and nectarine in the mid-Atlantic region, where injury associated with Cytospora canker, pruning wounds, winter injury, and mechanical damage results in significant loss of production in older orchards.

II. Hosts: Peach and nectarine are the preferred hosts, but all stone fruits may be attacked. It may be common in black knot galls on plum.

II. Description: Adults are 1/2 inch (13 mm) long, clear-winged moths that resemble wasps (photo 1-120). The wingspan is 5/8-1 inch (16-25 mm). Females are somewhat larger than males. Both sexes are metallic blue-black with pale yellow bands on the second and fourth abdominal segments. Eggs are oval, cinnamon colored and <1 mm in size (photo 1-121). Mature larvae (photo 1-122) are 3/4-1 inch (19-25 mm) long, with a yellowish-brown head and creamy white body. The pupal stage is light brown and about 1/2 inch (13 mm) in length. Cocoons, in which pupation occurs, are constructed of pieces of bark and frass (larval excrement) held together by silk. Initially yellowish-brown in color, cocoons become rust brown as they age.

IV. Biology: LPTB overwinters in galleries under the tree bark as a larva in various stages of development, ranging from young to nearly full-grown. In the spring, larvae resume feeding and complete their development beneath a thin layer of the bark surface from pink to shuck fall. Following construction of a cocoon, the larva changes to the pupal stage. In 3-4 weeks the pupa pushes through the cocoon and the thin bark surface, the pupal case splits open, and the moth emerges. Empty pupal cases remain protruding from the bark (photo 1-123). Moth flight begins around shuck split or shuck fall and continues for 6-8 weeks. A second generation occurs from July through September (fig. 1, at bottom). Moths are active during the day, with mating and egg-laying occurring soon after emergence. Female moths are attracted to damaged and previously infested trees, and deposit eggs in cracks or under bark scales of wounded sites. Eggs hatch in 7-10 days and larvae burrow, feed and develop in the inner bark and cambium tissue for 40-60 days.

V. Injury: Infestation is almost always associated with previously damaged trees. The problem tends to be more severe in older orchards that have a greater incidence of Cytospora canker, winter injury, and pruning and other mechanical wounds. LPTB infestation occurs in these damaged bark areas from the ground to a height of 8 feet (2.4 m), with the majority in the upper trunk and scaffold limbs (photo 1-124, 1-125). Older wounds appear dark due to the exudation of gum which oxidizes. Larval feeding enlarges the wounded area which eventually results in complete girdling of the trunk or limb. The primary and earliest impact is a gradual decline in production on damaged limbs, which when girdled will break under a fruit load. With time, tree loss will occur from trunk girdling. LPTB feeding can also afford entry for disease organisms, eventually resulting in limb and tree death.

VI. Monitoring: Use pheromone traps to monitor male moth (photo 1-120) emergence. Inspect wounded areas (photo 1-124) on the upper trunk, scaffold limbs and branches when moth flight is increasing to determine the average number of empty pupal cases/tree observed protruding from the bark (photo 1-123). Begin inspecting wounds for fresh gum mixed with wood borings and sawdust-like frass (photo 1-125) approximately 3-4 weeks after the start of moth flight for each generation. Clear gum without wood borings or frass is not the result of borer injury. A management strategy should be implemented if there are more than a total of 2 larvae or empty pupal cases per tree for each generation.

VII. Management: Maintaining tree health is important for the management of LPTB since only previously damaged trees become infested. Pruning at the proper time of the season with the correct technique will help to keep LPTB populations low by reducing the incidence of Cytospora canker. Care should also be taken to avoid damage to trees by equipment used in orchards. LPTB may be controlled in either the first and/or second generation. Good control of adults can be achieved with an airblast sprayer application of a pyrethroid insecticide (Ambush, Asana or Pounce) when moth flight is peaking as determined with pheromone traps. Blocks that receive a pyrethroid application should be monitored closely for mite outbreaks. An alternative, and more effective strategy, is to either control larvae of the first generation in June with endosulfan (Thiodan), or the second generation after harvest with Lorsban. Both treatments should be applied in high pressure situations where wounds are numerous. Sprays targeted against the larval stage should be applied with a handgun directed at all wounds on the trunk, scaffold limbs and small branches.

Peachtree Borer, Synanthedon exitiosa (Say)

I. Introduction: Peachtree borer (PTB) is a native North American pest that has been known since colonial times. It is generally not as important as LPTB in the mid-Atlantic region, however, localized severe infestations have occurred. Unlike LPTB, PTB can become established in a healthy tree and can cause death of young trees in a single season.

II. Hosts: PTB is a most serious threat to peach and nectarine, but all commercial stone fruits and wild plum, cherry, and related plants are susceptible to injury.

III. Description: Adults are clear-winged, metallic blue-black moths that resemble wasps. The male is similar to LPTB, but larger and with narrow yellowish bands on the third through the fifth or sixth abdominal segments (photo 1-126). The female is slightly larger than the male, with a broad orange band on the fourth and fifth abdominal segments (photo 1-126). The female has dark blue and opaque forewings and clear hindwings, whereas both wings are clear with dark borders and a transparent amber sheen in the male. The wingspan is 3/4-1 1/4 inches (19-31 mm). Eggs are oval, cinnamon to rust brown, and <1 mm in size (photo 1-121). The larva is cream to dirty white with a yellowish-brown to dark brown head, and may be >1 inch (25 mm) long when full-grown (photo 1-127). The pupal stage (photo 1-127) is brown and 5/8-3/4 inch (16-19 mm) long, with the orange band visible on the female just before emergence. A rust-brown cocoon is constructed of frass, wood and soil particles held together with silken threads.

IV. Biology: PTB overwinters as various larval stages in burrows under the bark at or near ground level. Larvae resume feeding and complete their development in the spring and early summer. A cocoon is constructed in an upright position just beneath the soil at or near the tree trunk. After a 3-4 week pupation period, the adult emerges, leaving the empty pupal case protruding from the cocoon. Moth flight occurs during June to September, there being one generation per year (fig. 1, at bottom). Moths are active during the day, with females mating and beginning to lay eggs on the day of emergence. Each female deposits an average of 400 eggs within a few days on the trunk and on weeds and soil around the base of the tree. Adult females live only for about 1 week. Eggs hatch in about 10 days and larvae enter the tree through cracks or wounds in the bark near the soil line. Larvae feed and develop in the cambium layer until winter.

V. Injury: Larvae feed in the inner bark and cambium tissue of trees within a few inches above to below ground level. Feeding may also occur on large roots near the soil surface. Evidence of infestation consists of frass and fine wood borings mixed with gum at the base of trees (photo 1-128). Young trees may be completely girdled in a single season, resulting in death. Older infested trees are less vigorous and productive, and often succumb to other insects, diseases or winter injury before girdling causes death.

VI. Monitoring: Use pheromone traps for monitoring male moth (photo 1-126) emergence. Inspect the base of trees for an exudation of gum containing frass and sawdust (Photo 1-128). Determine the average number of cocoons and empty pupal cases in the soil at or near the base of the tree. A management strategy is recommended for trees up to 3 years old if any evidence of PTB infestation is detected. In older orchards, an average of more than 1 cocoon and/or empty pupal case per tree would warrant treatment. Experience has shown that populations seldom need treatment when trap catches peak at less than 10 moths/trap/week.

VII. Management: The postharvest treatment specified above for LPTB will also control PTB. The spray should be directed at the base of the tree to thoroughly wet the top few inches of soil.

Credits: Text prepared by H. W. Hogmire, modified from the original text in the Mid-Atlantic Orchard Monitoring Guide (original texts by H. W. Hogmire and D. F. Polk).

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