Return Of The Fall Armyworm?

JONATHAN L. LARSON 

LEXINGTON, KENTUCKY

In 2021, Kentucky was one of many states that were impacted by a historic outbreak of fall armyworms. That year marked perhaps the worst year for the pest since the 1970s and has inspired fear and dread about these hungry, hungry caterpillars rearing their head again. In the past week, reports from western and central Kentucky have indicated that some folks are seeing fall armyworms in turfgrass areas. It doesn’t seem to be at the same levels we experienced in 2021 but it doesn’t hurt to review how this pest works and what can be done about it.

Fall Armyworm & Kentucky

Fall armyworms do not overwinter in this state. They are a tropical species, and they typically overwinter in southern Florida and southern Texas. These spots stay warm enough for them to persist and then mate to start the generations that will migrate northward. They usually move from these toasty states into states like Mississippi and Alabama in April and May, arriving next in Tennessee by May or June. Typically, they start to appear in Kentucky by June.

In the Bluegrass State, fall armyworms are usually associated with issues in pastures and crops. In this state and others, they will cross over into the home landscape to feed on turf in lawns. Initially when they feed, the tips of the blades of grass will have windowpane-like damage. As the caterpillars grow, they will progress into consuming whole blades of grass. The term “armyworm” also comes from the fact that these pests move in a group across the grass, creating a distinct line of damage opposed to undamaged grass. Newly planted sod is more susceptible to being killed by these pests than established turf areas.

What should you do now?

If you live near pastures or agricultural production fields that have been affected by fall armyworm damage, it might be a good idea to check your lawn for initial signs of damage. Additionally, if you noticed large numbers of egg masses, it would behoove you to check in with your lawn. Infested stands of turf will appear thinned out, often with exposed crowns or soil where caterpillars have completely consumed the plant.

Some folks won’t have to worry. If you have a yard that was treated with Acelepryn or Scott’s GrubEx in the spring/early summer for grub control, you likely won’t get fall armyworms. These systemic products last through the whole summer and are effective against both beetle grubs and moth caterpillars.

If you haven’t had your yard treated, though, and are seeing a concerning amount of damage, you can minimize fall armyworms and their feeding with pyrethroid products like bifenthrin, cyhalothrin, and others. Bt and spinosad, which are organic options, will work when caterpillars are smaller and might be effective if another generation of armyworms develops here.

No insecticide will make grass green again though! If you have seen part of your lawn destroyed, you can salvage what is left, but prepare to reseed or resod in the near future.  ∆

JONATHAN L. LARSON: University of Kentucky