James V. Robinson, Extension Entomologist
Texas Agricultural Extension Entomologist
Extensive damage to peaches and plums is caused by the plum curculio. Holes appear in the fruit as the adults feed and deposit eggs. These holes provide entry for the brown rot fungus and produce catfacing on peaches similar to that caused by stink bugs. The larvae tunnel in the developing fruit.
The adults are snout beetles, about 1/4 inch long, gray to black with lighter gray and brown mottling. Their wing covers are roughened and bear two prominent humps and two smaller ones.
The larvae are curved, slightly white to yellow- white, legless grubs with brown heads. They measure about 3/8 inch long when full grown.
Adult plum curculios overwinter in protected places in woodlands, along fence rows and under ground debris. They begin to leave hibernating quarters before wild bush plums bloom and migrate to wild plum thickets and plum orchards and to a lesser extent to peach trees. They feed on the foliage and flowers until the small fruits form.
Shortly after the shucksplit stage on plums, plum curculios begin to lay eggs, but the peak of egg-laying is not reached until a month later.
Plums and nectarines are chosen as egg-laying sites by the overwintering generation more frequently than are peaches. However, peach varieties which mature in late May and during June also are attacked.
The females eat holes in the fruit and deposit their eggs. After having placed the eggs, they cut a crescent-shaped slit under each egg cavity.
The larvae complete their development in the fruit in 2 to 4 weeks. When full grown, they crawl out and drop to the soil where they construct an earthen cell, usually 1 to 3 inches below the surface, in which they pupate and transform to adults. These first generation beetles emerge from the ground in 3 to 4 weeks. The life cycle from egg to emerged adult requires 5 to 8 weeks.
Plum varieties that produce large fruit are more satisfactory as a host for the larvae than the wild bush plum. Twice as many curculios develop to adults in these varieties as compared to the small bush plums.
Most plum varieties are harvested by the time the first generation is completed and many of the adult curculios migrate to peach orchards.
Here, they deposit their eggs in the developing early to mid season peaches. The second generation larvae may be found in the peaches at harvest time.
After the second generation larvae have completed development, they pupate in the soil and appear as adults in July and August. They join the first generation adults in feeding on foliage until the advent of cold weather, at which time individuals from both generations seek hibernating quarters.
Annual variations in this life cycle depend on climatic conditions. During hot, dry seasons, fewer individuals of the first generation reach maturity and the second generation rarely gets large enough to inflict economic injury to peaches. The overwintering population, following a hot, dry season, is composed almost entirely of first generation adults.
Suggested Control of Plum Curculio in Peaches and Plums
Satisfactory control of the plum curculio depends on the careful application of effective insecticides. Normally, applications should begin at the petal fall stage of peaches and plums. Since economic damage occurs only to the fruit it is usually not effective to apply insecticides before this time. However, if the orchard has in previous years suffered heavy curculio damage or wild plum thickets are immediately adjacent to the orchard, an application of an insecticide at pink bud could be effective in reducing curculio numbers.
Regardless, three applications of an insecticide are needed for early curculio control. Apply the first spray at 75 % petal fall and make 2 additional applications at 7 day intervals. After this, follow up with cover sprays at 10-14 day intervals
Commercial producers may refer to TAEX publication B-1689 Insects and Disease Control on Peaches, Apricots, Nectarines and Plums for insecticide, rates and remarks. Homeowners please refer to TAEX publication B-5041 Homeowner's Fruit and Nut Spray Guide.
References to commercial products or trade names are made with the understanding that no endorsement is implied and no discrimination is intended by the Texas Agricultural Extension Service. Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socio-economic level, race, color, sex, religion or natural origin.
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Last modified: June 23, 1998 by Andrew Perrone