UMN Experts Advise Growers on Aphids and Crop Diseases

By Scout Nelson

University of Minnesota Extension specialists recently shared updates on soybean aphids, crop diseases and pest management strategies during the Aug. 12 Strategic Farming: Field Notes program. Experts Anthony Hanson, Extension Educator in Integrated Pest Management, and Dean Malvick, Extension Plant Pathologist, discussed current field conditions and key issues affecting Minnesota growers.

Soybean aphid populations have remained relatively low across the state, although some fields have experienced localized increases. Cooler temperatures may encourage population growth, but as soybeans approach the R6 growth stage and aphids begin migrating back to buckthorn, the need for insecticide applications declines.

Extension specialists reminded growers to follow established economic thresholds before applying insecticides. Treatment is generally recommended only when aphid populations reach an average of 250 aphids per plant and continue increasing.

The program also addressed alternative pest-control methods often promoted online. Researchers noted that claims about using sugar to control aphids are not supported by scientific evidence and encouraged growers to rely on independent research and field trial results before adopting unconventional practices.

Hydrogen peroxide has also been promoted as a low-cost option for managing white mold in soybeans. However, research has shown that properly timed fungicide applications provide better yield protection, while hydrogen peroxide treatments offer limited benefits.

Malvick said the optimal window for managing white mold with fungicides has largely passed because most soybean fields are beyond the recommended growth stage for treatment. He also reported that Sudden Death Syndrome (SDS) has appeared in fields with adequate rainfall, making resistant varieties and effective seed treatments important management tools.

Another disease drawing attention is red crown rot, which was identified in Minnesota for the first time last year and has continued spreading in neighboring states. Growers are encouraged to scout fields carefully and submit suspected samples for testing.

In corn, both southern rust and tar spot have been detected at low levels during the 2026 growing season. Favorable weather conditions and advancing crop maturity have reduced the likelihood of either disease causing significant yield losses this year.

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