Armyworm caterpillars scalping turf in some places

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

The big flight of armyworm moths into Michigan back in mid-June has resulted in enough caterpillars to cause turf injury in a few places. Outbreaks are often found in turf under or near bright lights. What happened is the moths were attracted to the lights and settled nearby. Some of the female moths deposited eggs in the turf near the lights, resulting in hundreds or thousands of hungry armyworm caterpillars in early July. By the second week of July the caterpillars were nearly full grown, eating much more than they did when they were small.

Elly Maxwell at Dow Gardens found 5 to 10 armyworm caterpillars per square foot at one place in the gardens, and sent a few photographs of the turf injury. Heavily infested turf turns brown because all the green grass blades are eaten down to the ground, causing the “scalping” damage. Although it looks bad, the scalped area usually recovers quickly after the armyworms are gone. The armyworms have started pupating, so the feeding damage is almost over for this year.

Don’t worry about continuing problems with the armyworm. Elly said 75 percent of the caterpillars had little white eggs stuck to their bodies. These are the eggs of a tachinid fly parasite. The female fly glues eggs onto armyworms. When the eggs hatch, the fly larvae tunnel into the caterpillar eventually killing it. Several other parasites also help keep the armyworm under control. 


Armyworm damage.


Armyworm damage.

Dr. Smitley's work is funded in part by MSU's AgBioResearch.


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