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New England Blade – 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 (warm- and 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 redish brown cocoon), then emerges as a moth. Some moths will remain in the region, deposit eggs to become the 2^nd 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 3^rd-4^th 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 later instars… we can assume that the moths entered the region sometime around the end of July. Years where there are large storms/hurricane activity in mid-summer would allow for ample time for the moths to arrive in the north and develop to larvae where their feeding is very apparent. It’s possible that FAW do frequently make it to Pennsylvania but arrive too late in August to develop to large larvae (i.e. cause massive turf loss) before experiencing freezing temperatures. 

What should I be aware of next year?

I do not think that FAW is a pest that we can expect to be an annual issue in Pennsylvania. However, with changing climates and increased storm activity (and power), it is possible that we could see more consistent dispersal of FAW moths into Pennsylvania on annual basis. At this point in time, I don’t think FAW is a pest where preventive measures should be put in place prior to arrival (in Pennsylvania). However, there are opportunities where prevention of other pests will reduce the likelihood of FAW damaging turf stands. Those managers that used chlorantraniliprole (Acelepryn) for preventive white grub control were sleeping well at night during the FAW scourge of 2021. This preventive measure continues to provide exceptional control of white grubs and caterpillars when applied in spring. I received many photos of distinct lines between Acelepryn-treated and damaged turfgrass lawns or golf course fairways in 2021.

There are numerous curative control options for those that do not experience white grub issues or who have higher tolerances for insect damage in general. This approach can be effective but must combine scouting with timely interventions. Hindsight is always 20/20 and with turf loss to FAW still fresh in our minds, Pennsylvanians should be on the lookout for early arrivers in mid to late July rather than waiting until damage occurs in late August (or even later as observed in previous years). Caterpillar control in general is pretty simple and we live by a few tenets: 1) treat them early in their development, 2) apply contact insecticides to the foliage 3) don’t water it in or mow it off and 4) apply late in the day so the caterpillars acquire the residue while foraging. Pyrethroids are probably the most efficacious contacts available, but spinosads and indoxacarb are “softer” chemistries. Entomopathogenic nematodes are a great biological (non-toxic) option, but require some attention with storage, handling, application, and post-application care. If you have a weedy lawn like me- then doing nothing is also a viable alternative. Although FAW damage can be severe, the recovery on mature turfs is surprisingly good with light and frequent watering and a little fertilizer.