Feature
Looking Back at the
Fall Armyworm Invasion of 2021
By Ben McGraw, Ph.D.
It
would have been difficult to convince me in January 2021 that there would be a bigger insect news story than the emergence of 17-year periodical cicadas. These red-eyed menaces were the talk of the town early in summer with their near constant humming, driving those who work in landscapes to near madness over the course of several weeks. Little did we know at that time that a more insidious pest would be on the verge of invading the Commonwealth and about to cause turfgrass damage on a scale that has not been observed in many years. Here we look back at the Great Fall Armyworm (FAW)(Spodoptera frugiperda) Outbreak of 2021 to discuss what can be done in future years to prepare.
Homegrown problem: The majority of our destructive turfgrass insect pests are introduced species to North America. Invasive insects are believed to be more problematic outside of their native distribution since they are unlikely to occur along with their natural enemies, thus allowing for greater population growth. Unlike the majority of white grubs species, mole crickets, crane flies (leatherjackets), the FAW is native to the Americas. However, they are native to tropical or semi-tropical areas and incapable of persisting year-round in most areas in the United States. This means that no stage is capable of surviving in areas that experience freezing temperatures, limiting permanent populations to southern Texas and Florida. Each spring, moths in these areas deposit thousands of eggs that will hatch and become caterpillars. These voracious eating machines will feed on numerous host plants including corn, soybeans, rice, and turfgrasses (warmand cool-season turfgrasses). The literature would suggest that most turfgrasses are susceptible, including Bermudagrass, fescues, ryes, and blues. The caterpillar develops through six to seven instars, pupates in the soil (forming a reddish brown cocoon), then emerges as a moth. Some moths will remain in the region, deposit eggs to become the 2nd generation of caterpillars. This scenario will play out continuously, making for year-round threats to turfgrass loss in the south. However, some moths will be dispersed on the wind hundreds of miles which then become infestations in northern and western regions. The number of FAW generations a region may experience is largely dependent on the moth’s migration north. The Carolinas might have several FAW generations per year, whereas Pennsylvania and points north may experience one generation per year. Surveillance of moths has shown FAW capable of being dispersed as much as 500 miles in 24 hrs! The Northeast does not typically experience FAW turfgrass damage, but rather observe boom years when southern storm activity is active in mid-summer.
Why were FAW so bad in 2021? I have only witnessed one such destructive outbreak this far north in my career, but it was limited to a much smaller region (western NY). It is unclear as to how FAW populations reached outbreak levels so uniformly across Pennsylvania this year. Some theories are that insecticide failures are becoming more common in the South, leading to larger populations to disperse northward. We don’t expect to see FAW each year, much less such strong insect activity late in summer. Therefore detecting these insects usually occurs when they are 3rd-4th instars and turf is beginning to turn droughty. Given that the majority of the damage we observed in Pennsylvania was in the last week of August... and applying a little back calculations on the larval development time to reach these 16 Pennsylvania Turfgrass • Winter 2022
