–by Dr. Jeff Whitworth and Dr. Holly Davis
In 2017, thistle caterpillars caused considerable concern and some defoliation all around the state, especially in double-cropped soybeans. Thistle caterpillars are the larval stage of the painted lady butterfly.
Thistle caterpillars have been a perennial concern in commercial sunflowers, but in 2017, there were significant infestations in soybeans, causing enough defoliation to require many acres to be treated with insecticides. The painted lady butterflies then migrated south, out of KS, last fall as they don’t overwinter here. However, they are now migrating back into the state and are depositing eggs on sunflowers and soybeans. Thus, thistle caterpillars will soon be webbing together, and feeding on, leaves. In 2017, there were two generations and there is no reason not to expect the same this year.