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Armyworms are here....arm yourself

Fall Armyworm Egg Masses in Iowa

Perhaps you have seen the social media posts from those in southern states over the past couple months about fall armyworms on their yards, golf courses or athletic fields. The populations in those states have become greatly elevated compared to normal years. Occasionally, when this happens a storm can bring these pests to Iowa. Dr. Donald Lewis, entomologist at Iowa State says he can count the number of armyworm outbreaks in his career for Iowa on a single hand.

The winds will blow the adult moths up into an area and they will lay eggs. A single female moth can lay 500 eggs in a single grouping. Typically, these eggs can be found on or near a food source like a stand of turfgrass, or tree leaves overhanging turfgrass. The next step in the life cycle is the damaging one, the caterpillar stage. The caterpillar stage will devour a stand of turfgrass. Often they eat the blades down to the crown; the crown can desiccate and dry out without the shade of the blades. Fall armyworms do not overwinter in Iowa, so the upcoming cooler temperatures at night could help lessen damage in the state.

The first reports of egg masses were on Monday from turfgrass managers. Most of the egg masses seen so far have been on flagsticks, buildings, trashcans, and houses. The moths are depositing the eggs where they are landing. Eggs that are deposited on buildings and other non-turfgrass areas can be scrubbed off to remove. Many of the caterpillars will die before making it to the turfgrass to feed. There are differing reports on how long from the egg stage to the caterpillar stage with some saying as little as two to five days and other say five to seven days. Field crop agronomists have reported seeing damage from fall armyworms in alfalfa fields as well as in some cornfields in southern Iowa. It is not uncommon for fall armyworms to move from crop fields to turfgrass stands. Some suspected damage has occurred in the Burlington area of the state so far in turfgrass. As of writing this, I still have yet to see a caterpillar and that is why I have don’t have a picture of an adult included. If you do see one please send me a picture at The moths are drawn to light, so check in areas near lighting for egg masses and first signs of damage.

As always, we encourage you to identify a pest before treating for it. If chemical control is warranted, you would only treat during the caterpillar stage. Also, be aware that some agricultural producers have reported poor control with pyrethroid insecticides due to suspected resistance. If you have experienced damage, applying a fertilizer and keeping the area supplied with proper water will help speed up recovery.

For more information, please visit the Iowa State University Home and Horticulture Pest News link, as well as the Ohio State University link that has excellent pictures of the moths and caterpillar stages.

I will try to keep updates coming as warranted. Please do not hesitate to reach out with any questions- 515-294-1957.

Adam Thoms, Ph.D.

Turfgrass Extension Specialist

Iowa State University

Pictured 1 is Armyworm egg castings on a golf course flagstick in Central Iowa, Picture 2 is suspected damage to a lawn in SE Iowa, Picture 3 is a flag from the same golf course, Picture 4 is another view of the lawn damage

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