Fall Armyworm Management in Pastures and Hayfields

The fall armyworm (Spodoptera frugiperda) is by far the most important caterpillar pest in pastures and hayfields across the state of Georgia. These pests can quickly decimate a field of any forage crop, often selecting crops with greater nutritive value first.

If not controlled, fall armyworms can cause severe economic damage and total forage loss. While fall armyworms can damage many commodities in Georgia, this publication will answer the most common questions about the fall armyworm in Georgia pastures and hayfields.

How Do I Know If I Have Fall Armyworm Damage?

Unfortunately, fall armyworms usually go unnoticed until feeding damage occurs. The moths usually arrive in Georgia in the spring, originating from South Florida and the Caribbean. However, it usually takes several months for the population to build to a level where damage occurs. The damaging infestation does not occur until later summer or early fall in most years.

Damage can appear differently depending on the forage type and conditions. Fall armyworms prefer high-quality, well-maintained forage, and they will select higher-quality pastures and hayfields first.

Most damage begins with ragged leaves or areas with stripped stems (Figure 1). In hayfields or pastures that are ready for harvesting or grazing, damage can be devastating, with nearly all tender green vegetation being removed.

Often misdiagnosed as drought damage in overgrazed pastures, fall armyworm injury may appear as thinned grass and brown spots (Figure 2). The damaged patch will usually increase in size as the fall armyworm population builds. The brown color results from the dehydration of plant tissues following fall armyworm feeding. Often, tough stems will be the only vegetation left in the field after a severe fall armyworm infestation.

How Do I Identify Fall Armyworms?

Small fall armyworms tend to stay down in the canopy during the day, and their feeding is less damaging and harder to see (Figure 3). The youngest larvae do not eat much, but the large larvae (over ¾ in. long) can eat more than all other growth stages put together. Large fall armyworms are fairly easy to find because of their size. They are typically most active in the early morning or late afternoon when temperatures are cooler, but will feed throughout the day.