Fall Armyworms in Pastures, Alfalfa, Small Grains, Cover Crops, and Lawns

Fall Armyworm

Fall Armyworms in Pastures, Alfalfa, Small Grains, Cover Crops, and Lawns

We continue to receive questions on management with the unprecedented number of fall armyworms experienced in Nebraska this fall. See this previous Crop Watch article for more information. The following is a Q/A to address the specific questions we’ve received.

Q: I’m seeing browning in my crop, pasture, or lawn situation that happened within the past few days, but I don’t see any insects. Could this be fall armyworm?

A: It’s very possible as browning of leaf tissue from feeding does occur quickly with fall armyworms. It’s important to look for the fall armyworms near the soil line and also on the edges of patches where the plants go from browning to green. You may not always see them on the plants themselves in the brown areas, but typically people have found them both at the soil line and on the brown/green edges of fields/lawns when they looked.

Q: What is the threshold for fall armyworm?

A: A reasonable treatment threshold is finding 3 or more caterpillars per square foot within a field, pasture, or lawn. When considering a chemical treatment option, keep in mind caterpillars ¾ inch or longer are close to maturity and can be harder to control with an insecticide.

Q: My new seeding of alfalfa looked amazing and now it’s essentially gone. What should I do?

A: We’ve heard a number of reports of this and it’s hard to see this happen. If the armyworms are still present and feeding, there are a number of control options: active ingredients including the pyrethroids, Alpha-cypermethrin, Beta-cyfluthrin, cyfluthrin, Gamma-cyhalothrin, Lambda-cyhalothrin, permethrin and Zeta-cypermethrin, organophosphates, chlorpyrifos, and carbamates, carbaryl and methomyl. Organic options include Entrust SC and Neemix and products with Bt; these will work slower but are less likely to impact beneficial insects. This CropWatch article has more specific information.

It's important to watch regrowth. If reseeding is necessary, it may be wise to wait for reseeding till the spring with it being so late in the season.

Q: My established alfalfa stand is now sticks due to fall armyworms. I plan to get it cut off now, but should I also treat it?

A: We’ve heard several reports where the alfalfa was cut but the armyworms survived and are feeding on regrowth. It will be important to watch the regrowth and treat with the products listed in the previous question if necessary.

For those choosing between cutting and applying an insecticide, being this late in the season, it may be wise to hold off on cutting until the plants have had time to winterize and won’t try to regrow.

Q: In the past few days, I’ve gotten brown patches in my pasture. I’ve found armyworms and I currently have cattle grazing. Is there a product I can use that will save my pasture and not hurt my cattle?

A: Warrior II, Mustang Max, Beseige, Prevathon have 0 day grazing restrictions. You can see additional active ingredients, grazing, and haying restrictions at this website from Auburn Extension.

Q: I plan to plant wheat, rye, triticale for grain or a cover crop this fall. Should I seed now or wait to seed?

A: We’d recommend waiting to seed wheat till after the Hessian fly free date for your area. With the cooler weather, our hope is the armyworms will begin moving south. We unfortunately don’t know for sure when this will happen. One could wait till early October to seed small grains for grain or cover crop if you’d like to take a wait and see approach for the armyworms.

If you’d prefer seeding sooner, be sure to scout newly emerging plants. Insecticide options include products with active ingredients including pyrethroids, alpha-cypermethrin, beta-cyfluthrin, cyfluthrin, gamma-cyhalothrin, lambda-cyhalothrin, permethrin and zeta cypermethrin, organophosphates, chlorpyrifos and carbamates, carbaryl and methomyl. Organic options include products with Bt.

Q: My cover crop was obliterated due to armyworms. What can I treat it with and should I reseed?

A: This is the harder question to answer as cover crops aren’t listed on many insecticide labels. One approach is to look at a product you’re considering and see if any of the species in the mix, such as small grains, are listed on it. Also look for any grazing restrictions if you plan to graze the cover crop. Regarding reseeding, at this point in the season, we wouldn’t recommend anything other than small grains such as rye, wheat, triticale, barley for seeding due to the length of time the cover has before establishment and fall frost.

Q: My fescue lawn has rapidly turned brown and I’m finding armyworm in it. What can I use to treat it?

A: There are a number of products available in lawn/garden/farm and box stores. Read the label to see if fall armyworms are listed for control. Sevin is a commonly used product that is becoming harder to find in towns where fall armyworms are more severe. Organic options include products with Bt such as Dipel. Products should be watered into lawns to move the granules off the leaf surface down to the soil. Fescue lawns may need to be reseeded in the impacted patches. In lawns that are solely bluegrass or a bluegrass/fescue mix, the bluegrass should spread to help cover the impacted areas, so reseeding may not be necessary depending on the severity.

Q: Where can I find more information?

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