Hot, Dry Weather Raises Soybean Pest Threat and Yield Risks

By Scout Nelson

Hot and dry weather is placing stress on soybean crops and increasing the risk of insect pests. University of Minnesota experts say current conditions are affecting both soybean yield potential and pest activity across many growing areas.

Moisture stress causes soybean plants to close their stomata, reducing photosynthesis and limiting energy available for plant growth and seed development. Leaves may also flip to expose their lighter undersides, which is a common sign of heat and drought stress.

The R4 to R7 growth stages are critical for soybean yield development. Although drought has reduced top-end yield potential in some fields, timely rainfall during pod and seed fill could still help improve final yields.

Hot and dry conditions favor twospotted spider mites by increasing their reproduction and making drought-stressed plants more susceptible to damage. Dry weather also reduces the activity of naturally occurring fungi that help keep mite populations under control.

Farmers are encouraged to scout fields regularly, especially around field edges where spider mites often appear first. Checking the undersides of leaves for mites, webbing, and feeding injury can help detect problems before they spread.

Soybean aphid populations have remained relatively low this season, but cooler temperatures may encourage their growth. Experts recommend using established treatment thresholds before applying insecticides to avoid unnecessary costs and protect beneficial insects.

Researchers warn that resistance to pyrethroid insecticides is widespread in soybean aphid populations. In some cases, using these products on resistant aphids can worsen infestations by eliminating natural predators that help control aphid numbers.

Regular scouting through the R5 growth stage remains important for managing both spider mites and soybean aphids. Careful monitoring and informed treatment decisions can help protect soybean yields while reducing unnecessary pesticide applications.

Photo Credit: istock-oticki