Thistle Caterpillar in Soybeans

Jul 14, 2020

Thistle Caterpillar in Soybeans
Thistle caterpillar, known as the larvae of the painted lady butterfly, is a sporadic pest of soybean that feeds on leaves causing defoliation in the upper canopy of the soybean plant. Here are some insights to keep in mind as migration begins. 

  • The eggs are white to light green and in a barrel shape.
  • The larvae are around 1 & ¼ inch long and brown/black with yellow striping on both sides with branched, spiny hairs covering the body.
  • The adults look similar to the monarch butterfly. And are known for their unique black and orange “splatter” pattern. 

Life Cycle of the Thistle Caterpillar
Painted lady butterflies do not overwinter in Minnesota, but migrate from the south each spring. When they arrive, they lay their eggs on soybean plants. The eggs hatch and the thistle caterpillars can feed anywhere from 2-6 weeks. After that they form a chrysalis and then the butterfly emerges. Each season usually has 1-2 generations.

Scouting and Management
According to the University of Minnesota Extension, if thistle caterpillars are present in your fields, it is warranted to consider treatment at these guidelines- Examine a minimum of 10 plants:
  • Vegetative plants: treat if caterpillars are present and defoliation reaches 30%
  • Reproductive plants: treat if caterpillars are present and defoliation reaches 20%

Observed feeding from thistle caterpillar on soybean leaves - 35% defoliation on the left and right; 25% defoliation in the middle: Iowa State University Extension, Marlin E. Rice.

If you come to the conclusion that you need to treat for thistle caterpillars, bifenthrin and chlorpyrifos products will provide effective control. Tundra Supreme offers two modes of action for resistance prevention and outstanding control. With flexible application options; can be applied by ground, air, or chemigation. And effective, season-long control with long-lasting residual protection.

Be sure to get out and scout for thistle caterpillar and please contact your Central Counties agronomist with any questions or with help identifying pests and treatment options.


Read More News

Oct 25,2021
Learn more about Central Counties Producer of The Month, Chad Willis
Oct 13,2021
Get a headstart on your 2022 season and start planning- a good place to focus your efforts is revisiting your nutrient management program. While the season is still fresh in your mind, think about what you’ll need to do ensure that your crops have what they need to thrive next year. Soil sampling is essential for developing an effective fertility plan for your operation. Take advantage of these benefits of fall soil sampling to help your fields thrive in 2022. 
Sep 03,2021
Planting a cover crop for nutrient and erosion benefits can make a lot of sense. However, nutrient management can be tricky. Here are some factors to consider to determine if growing a cover crop is practical for you.