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Picking Off Pecan Weevils

By Tara Weaver-Missick
October 25, 2000

Agricultural Research Service entomologists are helping pecan farmers devise new strategies to control crop-damaging pecan weevils (Curculio caryae), pests that cost growers $14 million annually to control.

Older pecan trees have alternate years of heavy and light crops, called alternate bearing. Pecan weevils are attuned to trees’ production peaks. They burrow into soil surrounding trees and emerge to reproduce during the year when trees are most productive, every two years.

Researchers at ARS’ Southeastern Fruit and Tree Nut Research Laboratory in Byron, Ga., are studying weevil emergence behaviors to determine how many pests fly into tree canopies and crawl up tree trunks.

To control weevils, growers typically treat the canopy with pesticides, killing beneficial insects that would feed on other pecan pests such as aphids and mites. ARS researchers found that many adult weevils crawl to the trunk after emerging from the ground. If researchers can determine what percentage of weevils fly versus crawl onto trees, growers can use this information to treat specific tree portions, cutting down on pesticide use, which is good news for the environment.

ARS researchers are also working with University of Georgia scientists on developing a naturally occurring fungus, Beauveria bassiana, as a promising weevil control. In a preliminary field study applying a fungal “moat” around a tree, the fungus killed 90 percent of weevils during the first two days. The researchers will study changes in the fungus’ effectiveness and persistence over time.

Another promising weevil control study just starting at Byron focuses on microscopic, insect-killing worms called nematodes. The researchers will evaluate which out of 30 species of insect-killing nematodes is best at controlling pecan weevils.

ARS is the U.S. Department of Agriculture’s chief research agency.

Scientific contact: Ted E. Cottrell and David Shapiro, ARS Southeastern Fruit and Tree Nut Research Laboratory, Byron, Ga., phone (912) 956-6421, fax (912) 956-2929,,