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Plum Curculio

The plum curculio, Conotrachelus nenuphar (Herbst), is a weevil (a type of beetle). It is dark brown, 1/4 inch long, and has four humps on its back and a long (one-third of the body length) snout projecting forward and downward from its head.

The beetles overwinter as adults under debris in the woods or field margins and migrate into the fields at about petal fall. They migrate more heavily when temperatures exceed 75°F and are slowed significantly when the weather is damp and cool (below 70°F). Plum curculio is usually more prevalent on plants adjacent to woods, fence rows, and trashy fields.

Females lay eggs in shallow pits excavated on the surface of green berries. Usually, a single egg is laid in each berry, and a crescent-shaped scar develops on the surface at this site. Upon hatching, larvae burrow into the fruit where they feed on the pulp for about 2 weeks, many times causing the fruit to drop. Infested berries sometimes remain on the plant, however, and can contaminate harvested flats. Fully grown larvae leave the fruit, burrow into the soil, and pupate within an earthen chamber. The adults emerge about 4 weeks later. Most of these adults enter diapause after several weeks of feeding, but if green berries are still present, a few will mate and produce a second generation.

Infestations of plum curculio usually can be detected by examining green berries for the typical oviposition scar. These berries are usually the first to turn blue. Adult curculio are nocturnal, but they can be found early in the morning or late in the evening by shaking the branches of a bush over a white cloth that has been placed on the ground. Adults disturbed in this manner drop onto the sheet and feign death by folding their legs tightly against their body and remaining motionless. They can be easily mistaken for debris.

Because the weevil spends much of its life cycle on the ground under the bushes, frequent cultivation can facilitate its control. Effective control can be obtained by postpollination applications of broad spectrum insecticides. Make sure flowers have dropped from treated blocks so bees will not be killed.

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Plum Curculio

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