Fuzzy Brown Moths Abundant in Iowa

AMES, Iowa — The Iowa State University Plant and Insect Diagnostic Clinic said it has been the week of the fuzzy brown moths, or FBMs – the not-so-technical term entomologists use to refer to hundreds of moth species that fit this description. Many moth species can be called FBMs and several species have been flitting around Iowa in abundance.

The diagnostic clinic received numerous moths for identification this week. “Homeowners get concerned when there are so many moths around their home and crop producers have reason to be concerned because several crop pests fall into the FBM category,” said Laura Jesse, clinic director. “So far no serious crop pests have been among the specimens submitted for diagnosis.”

One FBM that crop producers watch for is the black cutworm. Jesse and others are monitoring black cutworms and made scouting recommendations to corn producers this week. 

“Pictures and reports submitted so far have been determined to be army cutworm moths and lucerne moths,” Jesse said. While the moths are a nuisance, Jesse does not recommend treating for them, for several reasons:

1. They don’t cause plant damage. If they eat, they only feed on pollen and nectar.
2. Spraying foliar insecticides is not a cost-effective option for these night-flying moths. Field applications are particularly not effective because the adults are not feeding on young corn.
3. Moth species that do not eat as adults will die in less than a week. This is expected to be a short term annoyance.
4. Reducing outdoor lighting near homes at night is the best way to keep the masses away from homes. They are attracted to windows as well, but as long as screens are in good repair they will not get indoors.
5. There appears to be a variety of species active right now so it is difficult to determine where they will lay eggs and whether or not the caterpillars will become a pest. At this point, it is just have to wait and see.

Lucerne moth caterpillars feed on a wide variety of plants and grasses including alfalfa. They are not considered pests in Iowa. Army cutworm moths also are commonly called “miller moths.” The adult moths are migratory and well known for gathering around homes and accidentally getting inside.

Normally the army cutworm moth migration is more noticeable in states to our west — Kansas, Nebraska and Colorado — but it seems that this year Iowans have the pleasure of more moths than normal, and earlier. Army cutworm moths are annoying, but harmless.

“We do not expect an increase in damaging caterpillars because moths are abundant,” Jesse said. “We will have to wait and see if there is more caterpillar activity than normal, but there is no need for preemptive treatments.”

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FBM PHOTO: Army cutworm moths can be variable in size and color. Photo by Whitney Cranshaw, www.ipmimages.org.