Bean leaf beetle
Several types of beetles, mites, and aphids have been active in soybean fields this year.
After bloom, soybean pest activity varies greatly from soybean aphids to numerous types of beetles — bean leaf beetle, Japanese beetle, flea beetles and more. There are also several caterpillars that feed on soybeans, including green cloverworm, soybean looper and thistle caterpillar.
“I’ve seen all these in soybeans this summer, plus a lot of other incidental pests,” Hodgson said. “Soybeans can typically handle quite a bit of leaf defoliation, so we should be paying attention to those pests that feed on the pod and seeds.”
Like most years, she said pest activity in fields is highly variable. Drought conditions can favor certain pests like twospotted spider mites and grasshoppers.
Drought-stressed plants will show visual injury before those fields with adequate moisture. “Bean leaf beetle and Japanese beetle are more abundant this year than in the last couple growing seasons, and they should be a scouting priority to protect fields,” Hodgeson noted.
Determining when to spray — the economic threshold — is based on crop value and control costs. Most thresholds are stable between the growing seasons such as for soybean aphid and Japanese beetle, Hodgson said. Others are based on plant quality and made on a field-by-field basis, such as the threshold for spider mites.
The type of pesticide used to knock down pests is dependent on the target pest and time of year. Usually, coverage
is the biggest issue later in the season as plants as accessing the lower canopy becomes difficult. For insect pests, pyrethroids and organophosphates are the two main options. Several miticides are available for twospotted spider mite and would be appropriate for this pest.
“Proper identification is important to distinguish target pests from accidental invaders or beneficial insects,” Hodgson said. “Use full rates of a single mode of action, like a pyrethroid or an organophosphate, with sufficient volume and pressure to have droplets reach the pests. Continue to scout fields until soybean maturity.”ResourcesSoybean Defoliation
- Plant Management Network (webcast)Visual Guide for Estimation of Defoliation
- University of MinnesotaField Crop Insects
- Iowa Soybean Association and Iowa State University Extension StoreSoybean Insects Guide
- Iowa State University
For specific insect management recommendations - contact your local agricultural Extension office