It’s that time of year when tassels are popping, soybeans are flowering, we’re making hay, and soaking up the sun – all the good things! Some insects love this time of year as well. I have collected some information on two corn and two soybean bugs to be aware of.

Japanese Beetles

An article published by University of Nebraska Lincoln stated, “Similar to corn rootworm beetles, Japanese beetles will scrape off the green surface tissue on corn leaves before silks emerge, but prefer silks once they are available. Japanese beetles feed on corn silks and may interfere with pollination.” University of Illinois Extension recommends: “An insecticidal treatment should be considered during the silking period if:

1. there are three or more Japanese beetles per ear,
2. Silks have been clipped to less than ½ inch, AND
3. Pollination is less than 50% complete.”

University of Nebraska Lincoln also suggested to be aware that Japanese beetle numbers are often highest on field margins, so scout across the whole field before making a treatment decision.

Western Bean Cutworm

Western Bean Cutworm infestation average one cutworm per ear, resulting in a loss of about four bushels per acre. Colorado State University published an article in 2014 stating that “Newly hatched western bean cutworms move to one of two places on the corn plant, depending on the stage of development of the corn. If silk feeding persists during pollen shed, pollination may be poor. Plant to plant movement is common and larvae from a single egg mass may infest nearby plants within a six-to-10-foot circle.”

“Once the ear has formed, it becomes the major feeding site for western bean cutworms, which feed on developing kernels. They reach the kernels through the silk channel or by chewing through the husks.”

Soybean Gall Midge

The most damaging stage of the soybean gall midge is the larvae as they feed on tissues within the soybean stem, disrupting nutrient and water movement within the plant. At this time, there are no research-based effective management strategies to suppress larvae. Anecdotal observations show early-planted fields are more susceptible to infestations and subsequent severe plant injury.

Signs that soybeans have been affected by soybean gall midge include darkening and discoloration near the soil line, followed by a gall forming (appearing as swelling, discoloration or outgrowth of the stem). Infested plants will quickly wilt and die or break off at the site of feeding.

To determine whether your plants are affected, look at the base of the first few rows of plants, checking for discoloration at or above the soil line. Carefully peel back the layers of the discolored potion of the stem with your fingernail to look for white or orange larvae. A hand-held can aid in seeing larvae inside stems.

Thistle Caterpillar

Thistle caterpillars are a sporadic pest of soybean, causing defoliation in the upper canopy of the soybean plant. Simply put, eggs are laid on the upper side of leaves of host plants, the caterpillars hatch and form webs by tying leaves together with silk. After two to four weeks, they form a chrysalis, which hangs from the host plant. Seven to 10 days later, the butterfly emerges.

Sources and more information:

University of Nebraska – Lincoln
Colorado State Extension
Iowa State University Extension and Outreach