Iowa's mild winter has accelerated insect development across the state this spring. Here's an update for early June. Recent sightings include soybean aphids, Japanese beetle adults, black cutworm, European corn borers and corn earworm.
"During the last week of May, I heard about a few insect sightings in Iowa," says Erin Hodgson, Iowa State University Extension entomologist. "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 aphids every year."
Winged females of soybean aphid deposit a few nymphs per day in May and June. You may need a hand lens to see first instars on small plants (see photo). "Often I confirm early-season colonies in soybean by looking for ants and lady beetles," says Hodgson, who provides a look in with a second photo that accompanies this article.
"Japanese beetle adults are starting to show up in central Iowa, as of the first few days of June," adds Hodgson. "Kelly Gill, ISU entomology graduate student, saw them destroying rose buds near the library on the ISU campus in Ames, Iowa (see photo). "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 nearby to Iowa, such as Illinois. They could be pests in corn and soybeans later in the 2012 growing season, but I am recommending that Iowa farmers keep an eye on their population densities of this pest already in June."
Black cutworm was still causing damage to corn in some parts of Iowa the first week of June. There were reports of significant stand loss due to feeding and clipping in young corn (see photo accompanying this article). Mark Carlton, ISU Extension and Outreach field agronomist at Albia in south central Iowa, reported some late-planted corn fields were being replanted in southeastern Iowa this past week due to stand loss by black cutworm. ISU's Hodgson recommends scouting for black cutworm until corn reaches V5 stage of growth. Read this ICM News article online at the ISU ICM newsletter website for more scouting information regarding black cutworm on corn.
Some other caterpillars are already showing up in corn. First generation European corn borer eggs and young larvae can be found on corn leaves (see accompanying photo). 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 in southern Iowa, also found a few corn earworm caterpillars in young corn last week. "This is a little early to see corn earworm in Iowa, but most insects are showing up 1 to 2 weeks earlier than normal this year," says Hodgson.