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UW study advises alfalfa growers on managing pesticide-resistant weevils

The UW researchers say that alfalfa weevils are growing resistant to commonly-used pesticides.

Big round bales of alfalfa hay are valuable both as a saleable commodity and as a source of protein for livestock. Inset: A weevil (Tyler Jones via UW; Joao Burini, Wikipedia Creative Commons)

CASPER, Wyo. — A University of Wyoming study conducted in Sheridan helped shape new recommendations for managing the effects of a problematic insect on alfalfa crops.

The study authors say that alfalfa weevils, which skeletonize the foliage of the valuable feed crop, are growing resistant to commonly-used pesticides. Growers should consider early harvests and other pesticides in certain cases, the study says.

“It is important for alfalfa growers to be aware that if they apply an insecticide to pests that are already highly resistant to it, they have wasted their money and increased resistance in that population,” said Scott Schell, UW Extension entomologist and co-author of the new publication.

The authors say growers should first be physically monitoring the weevil populations once the crop reaches 10 inches high to decide whether chemical interventions are warranted. 

Different approaches may be warranted whether the land is irrigated or dry, the study added. 

The researchers recommend tracking harvest quality as well as quantity. Alfalfa that is cut early but untreated can be marketed as higher quality, the study suggests.

The UW study can be found here.