Late Season Vegetable Visitor: Fall Armyworm

Reports are coming in from across the Midwest and now Minnesota that the region has received a late season influx of Fall Armyworm.  This pest only makes it to Minnesota from southern regions when we have just the right conditions and south to north airflow (similar to corn earworm).  

Fall armyworm caterpillars can be best identified by looking for a Y shape on their head.  They are often found clustered together in groups.

Fall armyworm feeding on grass. Note the upside-down Y going down the forehead and between the eyes. Gif: Marissa Schuh, University of Minnesota Extension.

Fall armyworm as a vegetable pest

Fall armyworm can be a pest of a few vegetable crops, though extension hasn’t gotten any reports of it feeding on vegetables this fall.  

It is most likely to be a pest of sweet corn, where it feeds on the leaves of pre-tassel corn, then moves to the tassel, and finally into the ear once it develops.  Most sweet corn production is wrapping up, so this isn’t a great threat.

Fall armyworm foliar feeding is often found in discrete areas of an infested field.  Affected areas will have lots of feeding. Photo: Marissa Schuh, UMN Extension.

Fall armyworm is also capable of feeding on peppers and tomatoes, though this isn’t common.

Fall armyworm in cover crops

The fall armyworm strain that appears to have landed in Minnesota is one that prefers to feed on grasses. As such, the place you may be seeing it is in cereal rye.  Signs you have fall armyworm include feeding, which can make grass look ragged or even expose the soil if feeding is extreme.  You might see extra birds attracted to the juicy caterpillars in infested areas.  If you suspect fall armyworm, visit the field in the early morning or as night falls, as fall armyworm is nocturnal. 

Fall armyworm often feed in groups, leading to clusters of damage. Photo: Chazz Hesselein, Alabama Cooperative Extension System, Bugwood.org

If you find fall armyworm, how much does it matter?

Depending on where you are in the state, you may have minimal growing season left.  Larger caterpillars are harder to treat, so depending on what size of caterpillars you are seeing, spraying may be futile for multiple reasons.

The growing point of the cereal rye should still be protected below ground, meaning the fall armyworm feeding matters very little.  Maybe plants will have slightly less biomass come spring.  Other grasses should survive, but may be weakened.

Fall armyworm cannot survive Minnesota winters, so save your worry for other end of season tasks. 

If you have pasture or hay and are concerned about fall armyworm, see Iowa State’s Fall Armyworm Management Considerations in Alfalfa and Cover Crops.