July 7, 2022
We didn’t apply insecticide on soybeans earlier because we didn’t see insects. Now stinkbugs are here. Should we spray? If so, what? How should we apply it?
This month’s Indiana certified crop advisers include Betsy Bower, agronomist for Ceres Solutions, Lafayette; Shaun Casteel, Purdue Extension soybean specialist; Greg Kneubuhler, G&K Concepts Inc., Harlan; and Bryan Overstreet, Purdue Extension educator, Jasper County.
Bower: Are you just seeing a few? Get a feel for infestation level. Stinkbugs are challenging because they typically arrive a little later than other soybean pests. They feed on pods and affect soybean quality more than yield. Poor quality can result in lots of dock.
To determine infestation level, sweep the tops and middles of soybeans with a net in five areas. If you find 40 stinkbugs or stinkbug larvae in 100 sweeps, apply an insecticide. The threshold is 20 per 100 sweeps on seed beans.
Several pyrethroid insecticides control stinkbugs. Note the preharvest interval. Some have a preharvest interval of 45 days, but most are 21 days. Apply with a ground rig or aerially.
Kneubuhler: Insecticide on soybeans is generally some of the best money spent each year. Stinkbugs are pod feeders, and if the pressure is high enough, it can make a yield impact. However, saying you need to spray simply because you see stinkbugs may not necessarily be the case. If stinkbugs are the ONLY thing you’re seeing, it’s worth buying a sweep net to get a handle on exact pressure.
Typically, if you average about 0.5 stinkbug per sweep, it’s worth spraying. We see stinkbugs almost every year, but pressures vary. Most generally, we like pyrethrin insecticides.
Overstreet: Sample with a sweep net or beat cloth to count stinkbugs. Take at least five samples across the field. The threshold is one bug per linear foot, or eight per 20 sweeps for commercial beans. Several insecticides labeled for soybeans are effective on stinkbugs. Spray by plane or chopper, if available. A high-clearance sprayer would also do a great job but leaves tracks. If an insecticide is warranted, please check the required preharvest interval.
Casteel: Scouting should be the foundation for these decisions. Green stinkbugs and brown marmorated stinkbugs are the two most common stinkbugs in Indiana. By now, soybeans are developing pods and beginning early seed fill. Stinkbugs damage soybeans by piercing pods and sucking out seed “juices.” They can damage soybeans through R5 and even beyond if pods stay green.
The current threshold for green stinkbug during this period is 40 bugs, adults and nymphs, per 100 sweeps, or 0.4 bug per sweep. Take 20 sweeps in five different areas of a field. If your field is above this threshold, apply a pyrethroid to control them. If it’s later in the season, check preharvest intervals.
Scout for other insects of interests as well as foliar diseases that might warrant an application. Applications with ground-based equipment will run over soybean rows, but plan to apply these products in the same pattern as your herbicide spray, or with a boom as wide as possible. That minimizes wheel track damage.
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