— by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa weevils are very active in south central and north central Kansas. We sampled many fields from 14 to 17 March and found small to medium sized (1st and 2nd instar) larvae in every field. Infestation levels ranged from 30% to 100+%.
Cooler weather over the next three days should slow down egg hatch and larval feeding activity. However, it does not look like the predicted low temperatures will be cold enough to harm either plants or weevils. Then, with the return of warmer than normal temperatures next week, the weevils will again become very active. Thus, if the winds are calm enough and fields are at or greater than 30% infested, next week seems like the ideal time to treat for alfalfa weevils. Only pinprick holes in leaves and a little feeding on terminals is evident so far. This, however, will quickly change if weevils are allowed to feed in 65+°F temperatures.