Kansas State University


Extension Entomology

Alfalfa Weevil Situation

–by Sarah Zukoff


I wanted to update you on the alfalfa weevil situation I’ve been dealing with. I’ve gotten many different calls from farmers and agents across Kansas the last few weeks. After working with Romulo Lollato in Ag; Judy O’Mara and Erick DeWolf in Plant path; Frank Pairs from CSU and Kelly Seuhs from OSU I think we have an idea of what’s going on. 


I received calls of extensive damage in alfalfa fields and multiple field failures of alfalfa weevil sprays-(see pic’s) in May. After visiting over 30 fields across the state and doing lab assays on collected larvae we’ve determined pretty wide spread lambda-cyhalothrin resistance with suspected resistance to Indoxicarb and even Chlorpyrifos. We’re setting up assays to test these later this year. The weevil damage was extensive and after multiple weevil sprays had little mortality. The frost hit after this damage and these very stressed plants died back pretty severely. These plants then experienced soggy spongy roots with some rot that further damaged plants. Larvae seemingly occurred in multiple rounds as the frost interrupted normal development.  I haven’t determined if the different weevil strains play into this story yet. So lots and lots of larvae that are literally STILL active in fields now with many sprays not working. After ten days, the plants are slowly bouncing back with yellowed regrowth. Farmers are struggling to find anything that works in some of these fields, consultants are being blamed for not doing their job, and agents are being pressured to find SOMETHING to help the farmers with… Therefore, I now need to quantify resistance to the other AI’s and ponder this delayed expanded hatching over two months.



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