Fall Armyworm Alert!
Dave Shetlar (BugDoc), Ph.D. & Shaohui Wu, Ph.D.
All summer, we have seen very little evidence of the fall armyworm (FAW) activity that was similar to the outbreak that we experienced in August through October of 2021. This year, our southern colleagues were fairly silent about FAW activities until late July and early August, when folks in Arkansas and North Carolina began to report of damage being observed in managed turf. At that time, we were still not seeing reports of any major numbers of adults being trapped in Ohio pheromone traps. Suddenly, in the first week of August, one of our agronomic crop entomologists reported getting significant numbers of adults in their pheromone traps. This last week another entomologist in the Lima, OH area also reported getting 100 or more adults in his pheromone traps. These reports trigger us to pay more attention to what could potentially happen in our managed turf. And, indeed, this week we began to get pictures from turf managers of FAW egg masses on structures overhanging turf. Therefore, we want to warn you of the potential for damage by FAW yet this season.
A Biological Timeline
FAW eggs, larvae, pupae and adults can’t overwinter here in Ohio. Freezing temperatures will kill all stages. Therefore, the adults that arrive in Ohio must have flown from more southern locations. This normally starts with detections in light traps and pheromone traps in the last week of June into the first two weeks of July. Those few adults will lay eggs on young corn leaves or structures overhanging green turf. The first generation of larvae are rarely noticed in Ohio because of the low numbers. Many of those larvae will be parasitized by tiny wasps that rely on our common armyworms, cutworms and other larger caterpillars as hosts. Each generation of FAW takes about 50-60 days to go through their complete life cycle (egg → five larval instars → pupa → new adult). So, by mid- to late August, we normally begin to capture 40-50 adults per trap per week. This level of adults, again, rarely produce sufficient egg masses to produce noticeable damage to managed turf.
The 2021 activity was very unusual in that we suddenly got 50 to 100 adults per trap in late July. These were obviously blown up to Ohio on storm fronts that occurred at that time. These adults produced sufficient eggs that resulted in visible turf damage in late August into early September. That first generation (in Ohio) then produced another damaging second generation.
With long-term weather predictions indicating that we will continue to have warmer than normal weather for the next two months, we have the potential that this unexpected FAW adult flight would produce sufficient eggs to result in damaging larval populations. This doesn’t mean we are destined for this to occur, but the potential is there.
Here is the possible timeline! The adults that have been noticed over the last two weeks may lay their eggs over managed turf. The adult females seem to be able to determine if their potential food is actively growing (i.e., the turf would be green). Egg masses can contain 100 to 400 eggs and the eggs take 7-10 days to hatch. The first instar larvae, drop to the turf below and feed within leaf folds for several days before molting into the second instar larvae. The second instar larvae then drop to the turf thatch surface and begin feeding, primarily in the evening and through the night. This continues until the larvae become fourth instars. At this time, they become “mowing machines.” This is the time that turf managers may notice that the turf canopy is beginning to thin. The larvae also will eat day and night unless extreme sunlight drives them down during the day. Fourth instar larvae usually take about 25-30 days from egg-laying to show up. The fourth and fifth instar larvae will feed for another week, and they can completely mow the turf down to the crowns. They don’t eat the crowns, but sun-exposed crowns can be desiccated or scalded, which results in their death.
The bottom line, if the recently noted adults have laid sufficient eggs over our turf to cause damage, this damage should begin to appear in the second or third week of September. If you are managing turf that has been kept green through irrigation, your turf is most at risk of a FAW outbreak.
Management
Be on the lookout for egg masses. This can alert you of impending larval activity.
Watch for thinning turf. We recommend doing a detergent flush in such locations to disclose any caterpillars that may be hiding in the thatch during the day. Joy and Dawn Ultra detergents have been commonly used. Mix two tablespoons of the detergent in two gallons of water. An old-fashioned watering can is an excellent tool. Apply this determent water over an approximate one square yard of the turf. Large caterpillars (i.e., armyworms or cutworms) will begin surfacing immediately after the application. Small caterpillars, like the spotted sod webworms, may take 15 minutes to emerge. If you begin to see little striped caterpillars, you are dealing with one of the armyworms. Common armyworm larvae will have distinctly light brown head capsules, but FAW larvae will have dark brown to black head capsules. With a hand lens, the FAW head capsules will have a distinctive, white, Y-mark.
If you have confirmed that you have FAW larvae and there are more than 10 in a square meter, quick treatment is needed. Fortunately, they seem to be susceptible to most of the pyrethroids; so pick your favorite pyrethroid and make the application as needed.
For turf managers that have detected many egg masses and wish to prevent any damage, a half rate of Acelepryn (or other Chlorantraniliprole formulations) should “prevent” damage for the time we have this year for caterpillar activities. We are worried that those who applied Acelepryn back in May may not be protected in September and October. It has been our experience that early Acelepryn applications provide about three months of protection. Hence, May applications have now been exposed to June, July and August weather, and residues may be below what is needed to protect the turf.