Can mid-season pest management improve soybean seed quality?

Soybean (Glycine max) producers in North Carolina have shifted to using early-maturing varieties to increase yield. This shift has coincided with high rates of seed damage and purple seed stain (PSS), sometimes resulting in dockage at the elevator. To better understand how pest management strategies affect seed quality, field trials were conducted in three environments across North Carolina during 2021-2022. When treated with fungicide and insecticide at growth stages R3 (beginning pod) and R5 (beginning seed), one out of six fields had a statistically significant reduction in both seed damage and PSS. At this location, stink bugs had exceeded the treatment threshold. As neither a fungicide treatment at R3 and R5 nor an insecticide treatment at R3 decreased the damage and PSS, the late-season insecticide application may be contributing to the reduction in seed quality issues.

As highly polyphagous feeders, stink bugs have been shown to transmit various pathogens to a wide variety of economically valuable crops across the United States. In North Carolina, the southern green stink bug (Nezara viridula L.) has the greatest potential to cause damage to soybeans. The causative agent of purple seed stain, Cercospora kikuchii, is spread incidentally to soybeans from the environment. At this time, direct transmission of C. kikuchii by stink bugs has yet to be investigated. In 2023, laboratory trials will investigate the potential of the southern green stink bug to mechanically transmit C. kikuchii to developing soybean pods, resulting in increased purple seed stain and reduced soybean seed quality.