While in westcentral Iowa yesterday setting up some small plot experiments, I got distracted by a long stretch of grass alongside a cornfield. I noticed some “deadheads” among the green plants and decided to dig a little deeper.
I pulled up some of the dead head plants and noted holes about half-way down the plant.
I was recently asked about an alien-looking caterpillar from central Nebraska. I occasionally see silver-spotted caterpillars in Iowa and wondered if you were seeing any in soybean?
The caterpillars are definitely a unique species because of the body coloration! The bodies are yellow-green in color and the head is brownish red. The caterpillars can make webbed nests similar to thistle caterpillar. They like to feed on locust trees, legumes, and wisteria.
After visiting several ISU Research and Demonstration Farms this week, our summer crew started seeing caterpillars in soybean plots. Many species are possible at once, but rarely do they cause economic injury in Iowa. Defoliation must exceed 20% after bloom to justify a rescue foliar treatment.
Thin Lizzy predicted it in 1976. Actually, the boys and girls are back in town. Over the weekend, the first painted lady butterflies were spotted in Iowa. Why care about this beautiful butterfly? It seems like a distant memory, but remember the thistle caterpillar bonanza on soybean last summer? They are one in the same species.
Corn earworm (Photo 1) is common in Iowa corn. It is a migratory pest, migrating from the southern and southeastern U.S. every summer. There are two general fights to the Midwest every summer, but the first flight is not of economic concern. Iowa’s corn is more vulnerable to infestation of the second flight, arriving in late July. Yield losses can occur in late-planted cornfields, where caterpillars can infest >50% of plants. It is more common to see corn earworm issues in sweet corn, white corn, popcorn, and seed fields.
Today in our corn efficacy evaluation trial, Ashley and our undergraduate team found small corn earworm caterpillars infesting ears (Figures 1 and 2). Caterpillars have a light-colored head but vary considerably in color from light green, tan, pink, maroon, and nearly black. However, they almost always have alternating dark and light lines running lengthwise down the thorax and abdomen and distinct tubercles (bumps) along the side of the body. They also have many black microspines on the body unlike most caterpillars with “smooth” skin.
Today for the first time this summer, I started to notice a few thistle caterpillars that didn’t look quite right. Some were very dark, some look deflated and some were kind of “slimy” in appearance. This happens to insects occasionally as a result of infection of an entomopathogen. That’s just jargon for “insect-killing pathogen.” There are several examples of these naturally-occurring pathogens, like fungi, bacteria, nematodes or viruses. Sometimes infected insects look discolored, puffy, or powdery.
After visiting several ISU Research and Demonstration Farms this week, it was evident the abundance and diversity of caterpillars in soybean is ongoing. These species represented several insect families. We easily found 8 species while looking at and sweeping early-reproductive soybean. Of course, thistle caterpillars were easy to find, but the interesting part is we saw a range of ages – from small to big caterpillars. I think it is a combination of first and second generation here in Iowa.
This year I’ve had a few people ask for tips on scouting for common stalk borer. The larvae are moving from brome to corn throughout Iowa and it is a good time to scout for timely management. Thanks to the help of Warren Pierson, coordinator of the FEEL, I have some photos to share.
Within the last week, I have heard about higher-than-normal stalk borer infestations along field margins compared to previous years. According to degree-day tracking of 2019, the caterpillars should be moving from overwintering hosts to corn throughout Iowa this week.
