Released: April 03, 2007

Unusually Early Alfalfa Weevil Activity Reported in Kansas

MANHATTAN, Kan. – Alfalfa weevils have already been extremely active throughout Kansas this spring, a Kansas State University entomologist said.

“Reports of alfalfa weevil activity have been pouring into K-State Research and Extension offices around the state,” said Jeff Whitworth, who is a 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 attributed 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 percent of the larvae were already in the 2nd instar stage and about 20 percent were in the 3rd instar. The others were 1st instars.

“From a practical standpoint, this means the majority of the feeding will occur over the next 10 to14 days, if the mild weather conditions continue,” Whitworth said.

Wet weather has been delaying much-needed insecticide applications, he said. 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 said. But, producers in central and southern Kansas would need to give the idea some thought, because larval development will be proceeding rapidly.

“As one consideration: When scouting for weevils during the first week or two of April, be sure to watch for pupae,” he advised. “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 said that samples from central Kansas taken the week of March 26-April 1 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.”

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Mary Lou Peter-Blecha
mlpeter@oznet.ksu.edu
K-State Research& Extension News