By Erin Hodgson, Department of Entomology
During the last week of May, I heard about a few insect sightings in Iowa. The first was a report by ISU Extension and Outreach Field Agronomist Brian Lang in northeastern Iowa. He saw a soybean aphid on VC soybean in his small research plot near Decorah on May 28. I wasn’t surprised, given that part of the state is where we usually first see soybean aphid every year. Winged females deposit a few nymphs per day in May and June. You may need a hand lens to see first instars on small plants (Fig. 1A). Often I confirm early-season colonies in soybean by looking for ants and lady beetles (Fig. 1B).
Figure 1. Soybean aphids start migrating to their summer host in May and June. A) Winged females deposit nymphs on expanding trifoliates. B) Colonies often will be tended by ants and can help with early-season detection while scouting. Photos by Brian McCornack, Kansas State University.
Japanese beetle adults are starting to show up in central Iowa. Kelly Gill, ISU entomology graduate student, saw them destroying rose buds near the library in Ames, Iowa (Fig. 2). We don’t typically see adults until mid-June in Iowa, but our mild winter has accelerated insect development. Japanese beetles have also been reported in other states like Illinois. They could be pests in corn and soybean later in the season, but keep an eye on their population densities in June.
Figure 2. Japanese beetles are strongly attracted to roses and other ornamentals. Eventually, they can be pests in corn and soybean. Photo by Erin Hodgson.
Black cutworm is still causing damage in some parts of Iowa. There are reports of significant stand loss due to feeding and clipping in young corn (Fig. 3). Mark Carlton, ISU Extension and Outreach field agronomist, reports some late-planted corn fields are being replanted in southeastern Iowa this week due to stand loss by black cutworm. I recommend scouting for black cutworm until corn reaches V5. Read this ICM News article for more scouting information.
Figure 3. Black cutworm can significantly damage young corn plants. A) Larvae often enter young corn plants above ground by making an entry hole. B) Cutworms curl up when disturbed. Photos by Jon Kiel.
A few other caterpillars are showing up in corn, too. First generation European corn borer eggs and young larvae can be found on corn leaves (Fig. 4). Older, non-traited corn should be scouted now to estimate densities. A dynamic threshold calculator.xls is available here. Tracy Cameron, an agronomist near Creston, also found a few corn earworm caterpillars in young corn. This is a little early to see corn earworm in Iowa, but most insects are showing up 1-2 weeks earlier than normal.