Cover Story

Unprecedented Fall Armyworm Pressure in the Mid-Atlantic in 2021

By Mike Goatley, Ph.D., Professor and Extension Turfgrass Specialist — Tom Kuhar, Ph.D., Professor and Entomologist Alejandro Del Pozo, Ph.D., Assistant Professor and Entomologist — Virginia Tech

Fall armyworms have been a statewide/regional problem on turfgrass systems across the Mid-Atlantic and upper South in 2021. Although it is of little consolation, if your turf has been attacked, we can assure you that you are not alone this year. Dr. Tom Kuhar, Professor of Entomology at Virginia Tech, details that in his 20+ year career at VT that he has never seen as much pressure from fall armyworms as he has this year. Here are some key points to share with your team and with your clientele for why the problem is so extreme in 2021.

We never quite know what each year has in store for us and our best guess this year is that fall armyworm pressure has been particularly high because of tropical weather systems/hurricane activity. The moths migrate northward every year, typically reaching the mid-Atlantic in early to mid-September (hence their common name of fall armyworm). This year, the moths arrived as early as we might see them. This is also of importance since it likely increases the number of generations of Fall armyworms we will likely have this year… normally 2–3, but maybe more than 3 this year? The reason they arrived early is likely linked to the number of named storms that have in some form or fashion either directly or indirectly influenced the mid-Atlantic region weather patterns in 2021. The moths are pushed along in the air streams of these major weather makers; in 2021 Danny, Elsa, and Fred have all had impacts in the mid-Atlantic. It might even be that Henri was a contributor to pushing moths further north and in greater populations than normal. Then there was Ida that tracked through the upper mid-Atlantic and Northeast. Ida almost assuredly brought moths along for the ride. This suggests we are NOT done with fall armyworm pressure for 2021 and that the problem with these pests will likely persist and possibly expand (although likely not as large in numbers as the first waves of the pest).

What else is in play with their numbers this year? The populations grow not from just moths arriving from the south, but those that are here are mating and laying eggs after they have arrived. A single moth can lay between 100–200 eggs at a time (usually on the underside of leaves) and lay up to 1500 eggs in their lifetime. During the summer, the life cycle can be completed in as little as 30 days. So, consider the pure scope of numbers of worms that are possible in this situation, and these numbers for a pest that essentially will feed on almost any type of aboveground plant material, while knowing that lawns, corn, and forage crops are usually favored targets. We have recently added an extension publication about managing fall armyworms in lawns to the VCE educational resources website (www.resources.ext.vt.edu).

Are the fall armyworms only attacking turfgrasses? A quick survey of fall armyworm feeding activity that was conducted by both the Virginia Turfgrass Council and agents with the Virginia Cooperative Extension indicates that fall armyworms have caused significant damage to tall fescue and bermudagrass in turf settings, but also to agricultural plants such as alfalfa, orchardgrass, and millet. In general fall armyworms have avoided crabgrass, sedges, and other broadleaf plants (things like dandelions, plantain etc.) in the lawns. There have been no reports of damage to corn, cotton, ornamental plants or vegetables.

What can be done as treatment? This greatly depends on your situation and the clientele you are serving. Lawn care providers have simply been overwhelmed by the sheer number of problems they encountered this year and there was no way to quickly service all of their clients. Insecticides recommended for control include most pyrethroids (such as bifenthrin, lambda-cyhalothrin, Mustang Max, Baythroid XL, etc..). Virginia Tech field trials on turfgrasses indicate very good control of larvae with the pyrethroids, which are also one the cheaper insecticide options available. Please note that control of large larvae is sometimes difficult with any insecticide. In surveying Virginia turfgrass managers, almost all that used the product reported that as a rapid, inexpensive, and highly effective knock-down fall armyworm treatment, granular formulations of bifenthrin have done an excellent job. However, these products are very short-lived in duration, and while the bifenthrin addresses the immediate control of the caterpillars, it does very little for long-term (i.e. residual) control if further generations of the insect emerge.

FIGURE 1. Fall armyworms can be identified by the inverted “Y” on their head (photo from Tom Kuhar).

The carbamate, Lannate LV, and many of the more selective (lepidopterantargeting) insecticides such as the diamides (Prevathon, Coragen, Acelepryn, Besiege), or indoxacarb products like Steward, Avaunt eVo, Provaunt, spinosad (trade names of Blackhawk, Tracer, Matchpoint), Radiant, Intrepid Edge, as well as others have strong activity on fall armyworms. Our surveys suggest that many Virginia turf managers that had applied clorantraniloprole (ai in Acelepryn) earlier in the year received very good residual control of fall armyworms. Chlorantraniloprole is a more costly product than any of the pyrethroids, but is an exceptional caterpillarcontrol product, offers an extended control period, and also serves as a very effective grubicide. Do note that chlorantraniliprole may take 2–3 days to actually kill larvae, but provides immediate feeding cessation, and thus stops damage right away even though the larvae are not dead. And remember that one of our most commonly applied insecticides for late summer grub control in lawns, imidacloprid, is essentially useless as a fall armyworm control product.

FIGURE 2. In just a few days fall armyworms have essentially defoliated this area of a tall fescue lawn

Consult the relevant Virginia Cooperative Extension Pest Management Guide for specific recommendations (https://resources.ext.vt.edu). Remember THE LABEL IS THE LAW and labels vary for products, pests, and the plants being treated.

Will the grass recover? Possibly. If the worms have not damaged the crowns (i.e. the growing points) the turfgrass will likely recover, especially with appropriate seasonal nitrogen fertility. The turfgrass recovery should be fairly evident as cooler temperatures and fall rains arrive. If the damage is extreme, regrassing (either by seeding or sodding) will be necessary. At this time, there are no varieties of tall fescue that are proven to be ‘resistant’ to fall armyworm pressure. However, it is always desirable to use the most improved genetics available and those cultivars can be found on the Virginia Turfgrass Variety Recommendation List (www.resources.ext.vt.edu). You can also find publications specifically devoted to lawn establishment and renovation on the website.