LINCOLN — Fall armyworms are continuing to be a problem in the eastern half of Nebraska causing significant damage to pastures and alfalfa fields. Unfortunately, the story is the same, producers watching a nice pasture or field nearly completely eaten down or turning brown in a matter of a few days by these pests. This is creating concern about newly seeded alfalfa, newly seeded small grains, and emerging cover crops.

We have seen a large population of Fall armyworm caterpillars this year, feeding on a wide host of crops and forages, doing most of their feeding and damage in the last 4 days of their larvae development. Because of this, it is very important to scout fields and pastures regularly in the early morning and late afternoon, when caterpillars are most active, to spot them when they are small. Once caterpillars are ¾ inch, they can do considerable damage in a few days. With winter around the corner, we want to make sure our pastures and winter crop fields have adequate time to prepare for a freeze. Severe damage now could impact the plant’s ability to winterize, leading to yield and stand issues next year. You also might consider delaying planting your winter wheat till early October.

Remember a reasonable treatment threshold is finding 3 or more caterpillars per square foot within a field or pasture. There are several insecticides labeled to control this pest. Mustang Maxx, Besiege, and Sevin can be used on pastures, alfalfa, small grains, and cover crops, but always read and follow the label. For forage crops be sure to check the grazing restriction and post-harvest interval. 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.

With cooler temperatures Fall armyworms feeding should slow down and the adult moths will eventually migrate south as they can’t survive Nebraska winters. Sadly, we don’t know for sure when that will happen. In the meantime, be sure to keep an eye on your pastures and newly seeded fields.

— Melissa Bartels, Nebraska Extension

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