Armyworms: True and Fall

Posted: June 18, 2012

Sweet corn growers usually deal with fall armyworms. This year we are also seeing problems of another species, true armyworm.
A healthy true armyworm and three killed by a pathogen, likely a virus. Photo by Mike Fournier and text from John Tooker —Penn State Extension

A healthy true armyworm and three killed by a pathogen, likely a virus. Photo by Mike Fournier and text from John Tooker —Penn State Extension

Armyworms: True and Fall

Shelby Fleischer, Penn State Extension, with text from John Tooker and an announcement from USDA Farm Service Agency

Sweet corn growers typically deal with a late summer arrival of fall armyworm (Spodoptera frugiperda).  This year, however, another species in the same insect family, the true armyworm (Pseudaleta unipuncta) has been infesting small grains and corn fields in record numbers.

Dr. John Tooker, Penn State Extension Entomologists reported about a week or ten days ago that “the caterpillars are living up to their names, marching across corn, wheat, and grass hay fields, over roads, into residential yards, and, even in some extreme examples, clogging up swimming pool filters! Activity will have to slow down soon, but these caterpillars feed more as they get bigger…Once caterpillars get closer to 1.5 inches, they will be getting ready to pupate. There are three generations of true armyworm each year and the expectation is that the second generation is rarely a problem and the third even less so. Given the extreme nature of this outbreak, however, I strongly believe there is potential for the second generation to be problematic in corn and grass hay fields. Growers would be wise to walk their fields and be on the lookout for a second generation during early July. For more details on true armyworm, see

We can also forward information that  “Representative Kathy Hochul (NY-26) announced … that the U.S. Department of Agriculture (USDA) Farm Services Agency (FSA) can now file weather-related disaster reports for damage done by armyworms due to the fact that they have arrived earlier than expected and in unprecedented numbers because of the unseasonably warm weather this spring.

“I am pleased to hear the USDA Farm Services Agency will now allow farmers to file weather-related disaster reports for damage done to crops from armyworms," Hochul said. "This is an important step toward the NYS Department of Agriculture and Markets declaring the armyworm infestation a disaster, allowing farmers whose crops have been devastated access to low-interest emergency loans to help in the recovery. I urge farmers that have been affected by armyworms to contact their local Farm Services Agency and report their loss immediately.”

Farmers should report their losses to their county Farm Services Administration to begin documenting the extent of the damage. If the FSA can document a countywide loss of 30 percent or greater for a single crop, they can then submit their data to NYS Department of Agriculture and Markets for a potential disaster declaration – allowing access to low-interest emergency loans.

In contrast to the true armyworm, the fall armyworm tends to arrive much later in the field season – sometimes late July or into August, sometimes not until September.  Part of the PestWatch sweet corn monitoring system using green/yellow/white bucket traps baited with lures to capture fall armyworm.  To date, we have not seen fall armyworm populations in Pennsylvania.  A factsheet on fall armyworm is at