Alfalfa weevil larvae were first detected this year in north central Kansas on March 3. Chuck Otte, Geary County Agriculture and Natural Resources agent, also reported finding small larvae on March 5 in Geary County and Tom Maxwell, Central Kansas District Agriculture and Natural Resources agent, also reported finding small larvae and pinprick-sized holes in new alfalfa leaves on March 9 in Saline County.
So, ready or not, alfalfa weevil larvae are here and, odds are that many more will be hatching in the next few days to weeks. Alfalfa weevils will continue to hatch and larvae continue to develop any time temperatures exceed 48 degrees F, - and those temperatures have been much more common than usual over the last few weeks. Forecasts for the next 7-10 days also call for warm conditions. Thus, it looks like larvae will be emerging, and damage progressing, relatively quickly.
Whether this warm weather will compress the alfalfa weevil larval feeding period so that the damage is not as stretched out as usual remains to be seen. There are also many lady beetles present in the alfalfa fields we have checked -- as well as a few pea aphids.
Treatment thresholds we use for alfalfa weevil insecticide applications are 30-50% infestation, or 1 larva for every 2-3 stems.
For more information on alfalfa weevils, please visit:
http://www.bookstore.ksre.ksu.edu/pubs/mf2999.pdf
Figure 1. Overwintering alfalfa weevil eggs in stem. Photo courtesy of K-State Department of Entomology.
Figure 2. Early instar alfalfa weevil larvae. Photo by Holly Schwarting, K-State Research and Extension.
Figure 3. Pinprick feeding damage by alfalfa weevil larvae. Photo by Holly Schwarting, K-State Research and Extension.
Jeff Whitworth, Extension Entomology
jwhitwor@ksu.edu
Holly Schwarting, Entomology Research Associate
holly3@ksu.edu
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