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Unusually early alfalfa weevil activity reported in Kansas

Agriculture.com Staff 04/03/2007 @ 9:24am

Alfalfa weevils have already been extremely active throughout Kansas this spring, a Kansas State University entomologist says.

"Reports of alfalfa weevil activity have been pouring into K-State Research and Extension offices around the state," says Jeff Whitworth, crop production entomologist with K-State Research and Extension. "The first calls started coming in from south-central Kansas about two weeks ago, which is three to four weeks earlier than normal."

Whitworth attributes the insect activity to unusually mild weather conditions that evidently caused alfalfa weevil eggs to hatch and larval development to proceed at a very rapid pace. Samples taken March 28 from fields in central Kansas indicated 60% of the larvae were already in the second instar stage and about 20% were in the third instar. The others were first instars.

"From a practical standpoint, this means the majority of the feeding will occur over the next 10 to 14 days, if the mild weather conditions continue," Whitworth says.

Wet weather has been delaying much-needed insecticide applications, he says. So, the next question is: If fields are too wet to treat for another week and the majority of the feeding and consequent damage is done soon after, will it pay to treat?

In the northern part of the state, generally north of U.S. Highway 36, treatment probably would still be worthwhile, Whitworth says. But, producers in central and southern Kansas would need to give the idea some thought, because larval development will be proceeding rapidly.

"When scouting for weevils during the first week or two of April, be sure to watch for pupae," he says. "If you are starting to find pupae and most of the worms are large, robust and maybe even a little sluggish, that probably means feeding activity is about to end naturally. So, you will not help the situation with an insecticide application. Also, if the alfalfa is growing rapidly, it may be prudent to harvest a little early, instead of treating.

"If you do treat, however, please pay close attention to the preharvest interval for the insecticide used."

Whitworth says that samples from central Kansas taken the week of March 26 showed no adults or eggs in alfalfa stems.

"It was a small sample. But, if we´re lucky and it´s indicative for other parts of the state, we may not have another `flush´ of egg-hatching and thus more damage," he said. "Even so, producers need to keep sampling and -- although it sounds crazy -- hope for a little dry weather."

Alfalfa weevils have already been extremely active throughout Kansas this spring, a Kansas State University entomologist says.

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