Army Worms on a haybine.

Thanks to a hurricane and an unseasonably warm September, alfalfa fields across the Midwest have become infested with army worms.

These worms are capable of destroying an alfalfa field in less than 24 hours. Pioneer Seed representative Troy Deutmeyer has been keeping a close eye on the infestation and reported that it has been affecting most of what is know as the “corn belt,” including Indiana, Ohio, Wisconsin, Minnesota, large parts of Iowa, and possibly even into Nebraska, although those reports are yet unconfirmed.

According to Deutmeyer, the army worm isn’t native to these areas, but is instead from the deep south and was brought to the Midwest by a hurricane. As the insects prefer lush green vegetation, many of the developed crops like corn were unattractive to the moths for egg-laying. Instead, they went for lawns, football fields, alfalfa, and possibly some cover crop fields.

He said, “There was a massive moth flight that got carried up into the Midwest with Hurricane Ida around a month ago. The moths came here and essentially started looking for the most green and lush vegetation to lay their eggs in. With the crop being so developed locally this time of year, that was primarily the alfalfa field.”

Deutmeyer said one of the biggest challenges in combating the pest is how quickly they reproduce, with moths laying up to 500 eggs at a time and the eggs only taking five to six days to hatch. Once hatched, they feed for approximately two weeks.

“Within several days of hatching they took some of those fields down to nothing,” he said.

While repelling efforts have been largely successful at keeping the population down, Deutmeyer said the recent warm temperatures might be fostering a second round of army worms.

“The insecticide application has been working fairly well. We’re getting maybe 75% killed, so it seems like it’s been enough to reduce the population to where the alfalfa is now staying ahead of the insects and growing faster than they can eat it. The army worm can complete its life cycle in 30 days in warm weather. Due to the unseasonably warm temperatures we’ve been having, I’ve had calls from customers who have fields with very small army worms, so we might be seeing a second generation or second hatch occurring. It’s something we need to keep our eyes on locally.”

Farmers are encouraged to keep an eye on their crop height for signs of stagnation due to the worms. Deutmeyer explained that if growth continues, it’s a good sign the army worm population isn’t high enough to cause significant damage. However, lack of growth may be a sign the fields need to be treated.

“They’ll be targeting the fields that were harvested seven to 10 days ago, and some of the cover crops that are starting to emerge, especially where people took silage off. I’ve had calls where some of those crops were four to five inches tall and have now been completely defoliated. If we are experiencing a second-generation, those are the fields likely to be targeted. What we’re telling guys right now is that if it looks like the alfalfa is staying ahead of the worms, you can probably let it go. If it looks like the alfalfa is just sitting there doing nothing or going backward, we need to treat. We’ve already had fields we needed to treat twice.”

While the army worms pose a legitimate threat to the alfalfa crops, Deutmeyer said they aren’t likely to have a major economic impact, although the exact future of the infestation remains unclear.

“The chances of economic damage on this second round are unlikely, but we’ve never seen this height of infestation. To be honest, we’re unsure what’s going to transpire here until we get a killing freeze that’s going to take care of these things. The reason we’re so concerned about the alfalfa fields is because this is the time of year where farmers are trying to prepare for winter and we want at least six to eight inches of regrowth. If the army worms aren’t allowing that to happen, we need to spray them.”

Luckily for farmers, infestations like this are rare occurrences due to the insects’ inability to survive Midwest winters. Deutmeyer said there should be nothing to worry about for next year’s crops, as the first major freeze should kill the entire population.

“They don’t winter here in Iowa. Once you have a freeze, they’re all going to be dead. Even the eggs can’t survive in the soil when it gets cold. They’ll be done for the year and have to travel from the deep south back into the state next year. That’s why we don’t see these insects in Iowa often. It’s rare years we see damage like this.”

Farmers are encouraged to reach out to professionals for inspection and treatment recommendations if they see signs of army worms in their fields.

Deutmeyer said, “Farmers can contact their local Pioneer sales representative, agronomist or Iowa State Extension and have them come out to look and see the extent of damage and if the crops are going to be able to outgrow it. A lot of us have been looking at a lot of these fields and have a better feel for what’s going on compared to if you’re just looking at it for the first time.”