Agronomy Library

Thistle Caterpillar

Paul Gaffney
June 26, 2019

Thistle caterpillars migrate north annually and have two generations. The painted lady butterfly will lay eggs individually on soybeans where they will develop in about 7 days. Caterpillars will feed for 2-6 weeks until pupation, which will last about 7-17 days.

  • Most injury damage will occur during V3-V4 soybean stages.
  • Larvae will web together the leaves of soybeans and consume about 37.5 inĀ² of tissue per larva.
  • Thistle caterpillars produce profuse amounts of dark brown frass pellets inside the webbed leaves.
  • Treatment recommendations would be warranted if fields reach 30% defoliation.