Fruit Crops News

Controlling Leafrollers With Bt

Leafrollers are a large and common family of moths that attack a variety of plants including both tree fruits and small fruits. Common fruit-infesting leafrollers in the Midwest include fruittree, redbanded, obliquebanded, and strawberry leafrollers, as well as others. Many leafrollers feed on a variety of plants, including common cultivated and wild trees and shrubs. Such plants serve as a reservoir for not only the leafrollers but also their natural enemies, all of which are very important in helping reduce the numbers of these pests. However, at times leafrollers will be numerous enough to cause injury to fruit plantings if not controlled. Being caterpillars, leafrollers are susceptible to control with sprays containing the insect pathogen Bacillus thuringiensis (Bt). For optimum control, proper timing of sprays is essential. Leafrollers use silken webbing to roll and tie leaves together, forming a protected retreat within which they feed. Usually these retreats are so tightly formed that sprays do not penetrate. Therefore, sprays have to be applied as soon as possible after eggs hatch, before larvae start to construct their retreats. On fruit trees, egg hatch of first generation leafrollers occurs before or during blossom; trees should be checked during this period and one or more sprays applied as necessary. Remember that Bt has only 1-2 days of residual activity. Egg hatch can extend over a 2-3 week period of time, so multiple applications may be necessary continue to monitor your trees through the petalfall period. Some leafrollers have a second generation (even a third in southern states), usually starting in June. The egg laying periods of most fruit-infesting leafrollers can be monitored with pheromone traps.

- Dan Mahr,University of Wisconsin

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