On June 14, Iowa State University extension entomologists put out a Pest Alert to scout for true armyworm because of statewide reports of this pest feeding on crops. In addition, there have been multiple reports, primarily coming out of northeast Iowa, regarding true armyworm feeding in hay and pastures. Now is the time to scout to determine if a treatment is warranted.
Plant Injury
Iowa State University’s IPM Team has monitored field crop pests for a long time. The pests have changed over the years, but the goal is the same: to help inform farmers about pest activity in Iowa. Our moth trapping efforts target migratory moths. Black cutworm monitoring is a long-standing project in Iowa, and true armyworm has been included since 2017. Since the timing of arrival is variable between growing seasons, trapping these pests helps us predict when injury will occur.
Although it has been uncharacteristically cold recently, it is officially springtime in Iowa and many insects are coming to life. One of the first things the field crop entomologists do each year is coordinate the Iowa Moth Trapping Network. Usually, these traps catch the specific species we are interested in, but there can also be a lot of bycatch.
Black cutworm (BCW) and true armyworm (TAW) moths continue to be active in Iowa. Last week, our cooperators in southern Iowa reported 37 total TAW moths. April 24 seemed to be the date with the largest flights: 14 TAW moths were caught around the state on that day alone. BCW moths were more widespread in Iowa compared to previous weeks. 31 BCW moths were caught across the state from April 22-24, but no significant flights have occurred yet (8 or more moths caught in a pheromone trap over 2 consecutive nights).
Despite the cold weather last week (April 12-18), moths were active throughout Iowa. April 13 had the most reports. Our cooperators around the state reported a total of 24 black cutworm (BCW) and 12 true armyworm (TAW) moths on that day alone. Figures 1 and 2 show the total moth captures in each county from April 12 to April 18 for TAW and BCW, respectively.
Moth trapping in Iowa is underway. Each year, we monitor field crop pests to help inform scouting activities in Iowa. In 2020, our moth trapping network includes black cutworm (BCW) and true armyworm (TAW; Figure 1). Both of these pests are migratory, making it difficult to predict where populations will establish year to year.
Each year, Iowa State University’s IPM team monitors field crop pests to help inform farmers and scouting personnel about pest activity in Iowa. This year, our moth trapping network includes black cutworm (BCW) and true armyworm (TAW), two migratory pests of crops in Iowa that are unpredictable year to year and thus require monitoring.
Armyworm feeding has been observed in several fields in northeast and southeast Iowa. Most of the fields with the feeding had cereal rye planted last fall and were terminated this spring.
Now is the time to be scouting for armyworms. Look for feeding on leaves. The larvae will typically begin eating on the lower leaves first. They start on the outer edges of the leaf and work their way in, leaving just the midrib. You may also find their frass pellets in the whorl of the plant.
By Adam J. Varenhorst, Mike Dunbar, Erin Hodgson, Department of Entomology
Scouting for adult true armyworms should occur in May and June in fields that are minimum, no tilled, or contains a cover crop. Feeding occurs on the lower corn leaves and moves upwards, but true armyworms do not bore into stalks.
