Every once in a while, soybean grain quality is down across a broad region, and yields are off, too. Elevator managers point to off-color soybeans and disease issues. But when specialists track down the cause, stinkbugs are the true culprit. Diseases develop once insects open pods to invading pathogens, even if it is only through tiny holes.

Don’t let 2024 be one of those years. Steve Gauck, a regional agronomy manager for Beck’s, based near Greensburg, Ind., says that’s one solid reason to scout soybeans all the way to the end of the season. Beck’s sponsors Soybean Watch ’24.

“We found a few green stinkbugs while scouting at the end of July in the Soybean Watch ’24 field,” Gauck says. “They were few and far between. However, insect populations can shift, based on weather shifts and other factors. Even if you have only found a few stinkbugs or other insects so far, I recommend continuing to scout soybean fields to make sure insects don’t show up in the latter part of the growing season.”

Know your stinkbugs

“Know your enemy” is the first rule of crop scouting. According to the Purdue Corn and Soybean Field Guide, green stinkbugs are typically bright green and shield-shaped when fully mature. Until then, color may vary. Nymphs can take on various colors and coloration patterns. Adults possess a straw-like mouthpart that can penetrate soybean pods.

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“That is how stinkbugs do the most damage to seeds,” Gauck explains. “They penetrate pods and sink that mouthpart into individual soybean seeds, sucking out fluids. That lowers yield potential at the same time. After damage, beans are often small and deformed.

“Plus, the pod is then open and vulnerable to disease pathogens. Remaining soybeans inside damaged pods often become infected with these secondary infections. That is why seed quality often deteriorates.”

Sometimes, brown marmorated stinkbugs show up in soybean fields as well. Mottled-brown in color, this species also uses straw-like mouthparts to penetrate pods and remove juices — and yield — from individual beans.

Purdue entomologists have set thresholds for spraying for green stinkbugs and recommend applying them to brown marmorated stinkbugs, too. Generally, brown marmorated stinkbugs tend to stay along field edges.

For green stinkbugs, consider treatment if you find 40 stinkbugs per 100 sweeps with a sweep net, assuming pods are still green. That works out to 0.4 stinkbug per sweep. In soybeans raised for seed, treat if you find 0.2 stinkbug per plant, or 20 per 100 sweeps.

From the field:
Soybeans head toward maturity

Crop condition ratings are reasonably good as soybeans enter the home stretch across the Midwest. Maturity is a mixed bag, behind normal in some states and ahead in others. Here is a closer look:

In Iowa. “Soybeans in southeast Iowa are deep green and healthy, as beans are at R6 and filling their pods. We are lacking moisture but have been enjoying moderate temperatures, although the week of Aug. 26 heated up. We could really use a rain to increase the size of those beans. Some shorter relative maturity fields have moved to R7, where at least one pod has turned color, and leaves are beginning to turn as well.” — Greg Shepherd, Beck’s field agronomist

In Minnesota. Condition of the crop is rated at 63% good to excellent, with 89% setting pods. That is eight days behind both last year and the five-year average. About 5% were turning color, compared to 21% in ’23 and 14% on average. — USDA National Agricultural Statistics Service

In Iowa. Soybeans setting pods reached 90%, nine days behind last year and three days behind average. And about 5% are turning color, vs. 12% and 9% for last year and the five-year average, respectively. Crop condition was rated at 77% good or excellent. — USDA NASS

In Nebraska. Soybeans are rated at 71% good to excellent, with 96% setting pods, compared to 89% last year and 92% for the five-year average. About 8% are dropping leaves, vs. 7% in ’23 and 6% on average. — USDA NASS