Skip to Main Content

Invasion of Fall Armyworms

The hot topic at the Extension office this past week has been fall armyworms. Farmers are finding fall armyworms in their pastures and hay crops, and homeowners are seeing alarming damage to home lawns.

The attack by fall armyworms this year may be a once-in-a-lifetime event. We rarely see this level of damage from fall armyworms in fields or in lawns.

Let’s start with farmers.

Dr. Keith Johnson, Purdue forage specialist, recently wrote that taking time to scout crops is very important, and those that did this “best management practice” had an opportunity to control the fall armyworm before extreme devastation occurred.

“Extreme defoliation of the forage is somewhat equivalent to a close grazing or machine harvest,” he said. “Availability of many approved insecticides with varying harvest restrictions was important to meeting the varying needs of producers.”

Dr. Johnson encouraged continued scouting of fields. “Do not take another machine harvest from damaged fields,” he said. “We are at the time of year anyway when the last growing season harvest should be completed.”

Dr. Johnson said if fertilizer is recommended by soil test, apply now as this may help weakened forages. “Avoid grazing extremely defoliated pastures for the rest of the year unless growth is abundant after plants are dormant,” he added. “If grazing occurs in the late fall, do not overgraze.”

Find Dr. Johnson’s article in the current Purdue Pest & Crop newsletter, Find a related article by Christian Krupke and John Obermeyer entitled, “Fall Armyworm Problematic in Late Growing Crops.”

Likewise, homeowners may have noticed recent damage to home lawns by fall armyworms. The damage may have first appeared as spotty, but affected areas can coalesce and move across the lawn in a slow wave (like an advancing army, hence the namesake).

Dr. Timothy Gibb wrote a recent article where he described fall armyworm. “Mature fall armyworms measure 1½ inches long with a body color that ranges from green to brown or black with distinct longitudinal stripes on their body,” he said. “They can be distinguished from similar caterpillars by the presence of a prominent inverted white ‘Y’ on their head.”

“Armyworm feeding usually is from the margins of the leaf toward the midrib,” he said. “This gives turfgrass a ragged appearance.” Gibb said that when infestations are high, most of the plant may be consumed.

“The key to controlling fall armyworm is early detection because infestations of fully mature larvae feed voraciously and can very quickly damage turfgrass,” he said. “Thresholds are not well developed for fall armyworm in turfgrass, but we suggest treatment when average counts reach two or three ½-inch larvae per square foot.”

While in a meeting with Purdue entomologists this week, they recommended applying insecticides very early in the morning, or very late in the day for best effect. Gibb had written in his article, “Be sure to apply insecticides only when periods of dry weather are expected so that the insecticide is not washed off of the leaves.”

Find Gibb’s original article at

Is there hope for recovery of turfgrass? Well, it depends. Time will ultimately tell.

A Purdue Extension publication by Douglas Richmond entitled, “Integrated Management of Turfgrass Insects,” states of armyworms, “Because they often go unnoticed while they are small, turf may seem to disappear almost overnight once these insects reach a larger size. Small patches of brown and overall ragged appearing turf are more typical symptoms. Fortunately, unless the turf is severely stressed by drought, it generally recovers well with irrigation or rainfall and adequate fertility.”

(Banner photo credit: Jeff Burbrink)

To Top