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Fall armyworms have been showing up in pastures and alfalfa fields across the region this fall, and producers are asking: what does this feeding really do to our forage, and what kind of recovery can we expect?
When infestations are heavy, armyworms can strip leaves quickly, leaving brown or stubble fields almost overnight. In fact, what often alarms producers most is how sudden the damage looks. A pasture that seemed fine one evening can look scorched by morning. The caterpillars feed mostly at night or early in the morning, then hide at the soil surface during the day.
In grasses, this defoliation reduces fall growth and weakens stands headed into winter. Most established pastures will regrow if the crown and growing points remain intact, but yield losses are likely. With damage coming so late in the year, recovery can take a while, and productivity often lags next year. Bare or thinned spots can also open the door for weeds next spring.
Alfalfa is another favorite target of armyworms. Established stands can generally recover if they have time and moisture, however new seedings are at much greater risk. Essentially armyworms act like a late cutting, so previous stand stress will impact survival and risk of winterkill. For new stands however, fall armyworm feeding can completely wipe out seedlings, leaving little option but to reseed next year. For producers who invested in new alfalfa this season, careful scouting is critical.
Worms will stick around until we start to get some cold temperatures this year, so active scouting now can catch infestations early and limit potential damage. But what can you do once the caterpillars are gone? First, evaluate the stand. If plants are actively putting out new growth, giving them rest from grazing or harvest can help rebuild root reserves before winter. In pastures, this might mean adjusting rotations to allow a recovery period. In alfalfa, cutting high and removing the stripped stems can stimulate regrowth, but again we have to be careful of timing at this point in the season. Second, think about moisture and fertility. Just like after drought stress, plants coming back from defoliation need every advantage. Adequate fall moisture is the biggest factor, but in some cases, a light fertility boost may help speed recovery.
Finally, watch for weeds. Thinned areas left behind after armyworm feeding are prime spots for winter annual weeds to sneak in. Monitoring those areas and addressing weeds early will help prevent long-term stand decline.
The bottom line? Most established pastures and alfalfa will recover, though fall growth and winter readiness may be set back. New seedings are much more vulnerable and often need to be reseeded. Careful scouting, timely harvest and grazing decisions, and post-infestation management all play a role in protecting forage stands from long-term damage.
-Ben Beckman is a beef systems Extension Educator serving northeast Nebraska. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 254-6821 or email: ben. [email protected] mailto:[email protected]
