This has been the week of the fuzzy brown moths or FBMs (as entomologists not-so-technically call the hundreds of moth species that fit this description). There is a wide variety of species that can be called FBMs and it seems we are experiencing several.
Some crop pests fall into the FBM category, and the sight of so many moths can cause concern. So far no serious crop pests have been among the specimens submitted to the clinic for diagnosis. "We already are monitoring for black cutworms and have recommended when to scout for caterpillars in corn," says Iowa State University Extension entomologist Erin Hodgson.
ISU specialists don't recommend treating these moths with an insecticide
Another ISU Extension entomologist, Donald Lewis, says "In addition to concerns about crop damage from these insects, there are questions about using insecticides to keep FBMs away from homes as they are bothersome. We do not recommend treating these nuisance moths for several reasons." He cites them as follows:
- Adult moths can be a nuisance, but do not cause plant damage. If they eat, they only feed on pollen and nectar.
- 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.
- Moth species that do not eat as adults will die in less than a week anyway so we expect this to be a short term annoyance.
- 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.
- There appears to be a variety of species active right now so we are uncertain where they will lay eggs and if the caterpillars will become a pest. At this point we just have to wait and see.
Pictures and reports submitted so far have been determined to be army cutworm moths and lucerne moths. Lucerne moth caterpillars feed on a wide variety of plants and grasses including alfalfa. They are not considered pests in Iowa.
Iowa has more moths than normal this year, and they're appearing early
Army cutworm moths are also commonly called "miller moths." (Fig 1) 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 the west of Iowa (Kansas, Nebraska, Colorado) but it seems that this year Iowans are experiencing more moths than normal and they are early this year. Army cutworm moths are annoying, but harmless.
The ISU entomologists add: "We do not expect an increase in damaging caterpillars because moths are abundant. Army cutworms and lucerne moths have such a broad host-range they often end up feeding on weedy plants in ditches and other areas. We will have to wait and see if there is any more caterpillar activity than normal, but there is no need for preemptive treatments."