Chemically treating for alfalfa weevils in early November may help reduce infestations the following spring – but it won't replace spring treatments.
That’s what Kansas State University (KSU) researchers are finding in trials evaluating whether insecticide applied after weevils lay eggs in fall will cut down on spring infestations.
“We’re not trying to eliminate the weevils in the fall,” says Jeff Whitworth, KSU research and Extension entomologist. “We’re just trying to reduce egg laying so that it will help out in the spring.”
Researchers are looking at alternatives to the traditional spring weevil treatment. Unpredictable spring weather makes it difficult for growers to spray before pests start doing damage. Adult weevils feed, mate and lay eggs in fall, but do much of their damage in a three- to six-week period in spring.
Whitworth's research began in 2012, after chemical companies received registration approval for fall applications of Stallion and Cobalt insecticides (see "Alfalfa Weevil Pesticides Get Special Registration").
He and colleagues began applying insecticide in early October, about two weeks after they detected the first adult weevil. Insecticides were applied to different test plots on Oct. 9, Oct. 23, Nov. 6 and Nov. 20.
The KSU team checked the alfalfa plots for weevils twice in April. The Nov. 6 application showed fewer alfalfa weevils per stem compared to the other applications.
While it was significant, the reduction was not large enough to prevent damage without a spring treatment, Whitworth cautions.
KSU’s team is continuing the research this fall and will evaluate fields again in 2014.
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