Fall armyworms (Spodoptera frugiperda) are periodic turf pests - they may not cause major damage every year, but occasionally, weather patterns (think hurricanes, severe wind and rain storms, and associated flooding) will create the perfect setting for a severe fall armyworm outbreak. And once these caterpillars get to munching, they can annihilate a lawn within a matter of days. So, how do you go about identifying, preventing, and managing fall armyworms?
Knowing your enemy – and knowing how to prevent and mitigate damage – starts with proper pest identification. The damaging stage of the armyworm, and the stage you’re most likely to notice and ID, is the “larvae” or the caterpillar.
Photo Credit: Blake Layton, MSU-ES, Alabama Cooperative Extension System
Adult armyworms are moths!
You may see armyworm moths flitting around between spring and fall. The moths are nocturnal, and are attracted to lights at night.
Photo Credit: Lyle J. Buss, University of Florida, UF | IFAS, Entomology
There will likely be multiple fall armyworm cycles, as larvae can hatch, feed, pupate into moths, and lay more eggs every couple of weeks in many regions!
Fall armyworms are often confused with other armyworms and various cutworms.
True armyworm (Pseudaletia unipuncta)
Photo Credit: True True Armyworms | University of Arkansas Extension.
Black cutworm (Agrotis ipsilon)
Photo Credit: Black cutworm on soybean | UMN Extension
Fall armyworms are most common in the southern and transition zones. Adult moths will lay hundreds of eggs on the undersides of leaves (especially those overhanging turf), or on light posts, fences, signs, patio or lawn furniture, and even on walls. Larvae will hatch and fall to the tuf below, where they will begin to feed. They prefer bermudagrass, but will also feed on fescue, ryegrass, bluegrass, bentgrass, and occasionally zoysiagrass. They can also feed on clover, veggies and crops, if nearby.
Fall armyworms are most active in summer and early fall. Adult moths can travel 500+ miles within 24 hours if there are large storms that blow moths along jet streams. This is why large fall armyworm outbreaks are often associated with above average rain and wind storms. Once the larvae hatch, caterpillars feed most actively mid-morning or late evening, but can often be seen feeding mid-day.
Fall armyworms are unique in their feeding pattern. As their name suggests, armyworms move across the turf en masse – much like an army marching across the lawn. The caterpillars wage war on the lawn by feeding on leaf blades, occasionally leaving a “windowpane” behind, but more often completely defoliating the grass within a matter of days. This leaves the crown (growing point) of the grass exposed to the elements, leading to heat and moisture stress, and even death. There will be a clearly defined line of damage that moves across the lawn rapidly, leaving a dead, defoliated yard in their wake.
Unfortunately, fall armyworms are difficult to control, partly because they act so quickly and can have multiple life cycles throughout the year. There are a few steps you can take to prevent damage, though:
Photo Credit: Grace Christopher, NBC | WFMJ
How to conduct a soapy water flush:
If your lawn does sustain some damage from fall armyworms, help it bounce back. Irrigate damaged areas to keep the crowns from drying out, and see if that helps the grass repair itself. Reseeding or patching bare or dead spots will also help bring some green back to the lawn.
Header Image: Pat Porter, Texas A&M Agrilife Extension, Alabama Cooperative Extension System
Alabama Cooperative Extension System. Controlling Fall Armyworms on Lawns and Turf.
North Carolina State Extension. Fall Armyworms in Turf.
North Carolina State University. Fall Armyworm Q&A.
The Ohio State University. Fall Armyworms March Across Ohio.
Purdue University. Managing Black Cutworms in Turfgrass.
Texas A&M Extension. Armyworms in Turfgrass.