– Christine Gelley, Agriculture and Natural Resources Educator, Noble County OSU Extension
Fall armyworm damage can appear to simply be the affect of drought. Closer inspection is warranted.
We have had numerous reports of fall armyworm egg masses in lawns, pastures, and hayfields in Kentucky and Ohio beginning in mid-August and now significant damage is occurring from the caterpillars throughout the state. Therefore, we must keep a close watch on pastures, hayfields, lawns, and gardens over the next few weeks. There is enough time left before winter that another generation of moths could lay eggs, hatch, and consume exponentially more greenery that this generation is consuming right now. Whether you were aware of fall armyworms before or this is the first time you’ve heard of it, you likely have some questions. Let’s address them:
How do I know if I have fall armyworms?
Treatment may be warranted when finding 2 or 3 worms per square foot.
Fall armyworm larvae are usually detected after someone notices extreme defoliation of plants that spreads across a space very quickly leaving waves of brown plant tissue in their wake. Once defoliation is apparent, you can usually walk into the damaged area and find the caterpillar larvae crawling on the plant material or on the ground. Depending on the stage of the caterpillar, they may be anywhere between an eighth of an inch long to one inch. They may be green or brown with yellow stripes and an inverted Y atop their heads. If you suspect that you have armyworms, but can’t see them yet, you can scout for them by pouring a bucket of warm soapy water on the suspected area to flush the worms out of the plant cover.
How did they get here?
Fall armyworm is a significant agricultural and turf pest in the Southern United States. Fall armyworm is rarely seen in Ohio, but many entomologists believe that adult moths from southern outbreaks were picked up in the storm front that came from the south recently. The adults of these moths have been known to travel 500 miles, even more, in 24 hours. They can get into the jet stream and move vast distances, then drop down to find suitable places to lay their eggs. We happen to be in the area where they dropped.
How long will they be here?
Fall armyworms will die after our first hard frost. As far as we know, they are not adapted to survive in Ohio. They will likely be a problem for the rest of the fall because there is enough time for another generation to hatch. After a female moth lays her eggs near a good food source, the larvae hatch out within two to three days. They stay in the larval stage (caterpillars) for two to three weeks while they munch on the leaves of over 100 different crops. Then they pupate for one to four weeks before hatching out as adult moths.
At what point should I treat for fall armyworms?
Large, 1 inch + fall armyworm is difficult to control. Treat them when still tiny.
If you have two to three caterpillars per square foot or more, then you should consider using an insecticide for treatment, because you will likely have considerable damage to late summer/fall growth in your pastures, hayfields, lawns, or gardens.
What can I treat with?
A variety of insecticides are labeled for use on fall armyworm. Your ability to secure and use them will depend on two factors: One- if the retailers around you have insecticides in stock. Two- if it is a restricted use pesticide or not. If the pesticide is labeled for restricted use, you must have a pesticide applicator license to purchase and use it. A list of recommended insecticides (active ingredients and brand names) for fall armyworm are listed below (referenced from Chris D. Teutsch, PhD- Extension Associate Professor and Forage Specialist at University of Kentucky). Take this list with you when you investigate products on the market and always read the label completely before use. There are restrictions for use and specific safety guidelines. In all cases, fall armyworm larvae are most susceptible to pesticide application when they are small. Few insecticides are effective on larvae that are an inch long.
- carbaryl ‐ Sevin XLR, Sevin 4F, etc.
- malathion – Malathion 5EC
- b‐cyfluthrin ‐ Baythroid XL
- g-cyhalothrin – Proaxis EC
- l-cyhalothrin – Warrior II
- a-cypermethrin – Fastac EC
- z-cypermethrin – Mustang Maxx
- methomyl – Lannate
- methoxyfenozide – Intrepid
- permethrin – Ambush, Permethin 3.2 AG
- pyrethrins ‐ PyGanic
- Bt products ‐ Agree WG, Biobit HP, Dipel DF, Javelin