Research Highlights

Managing White Mold with New Approach in Minnesota

By Barb Baylor Anderson

Minnesota soybean farmers have lost about $56 million in yield per year over the past five years due to white mold. In 2017, a particularly bad year, farmers lost an estimated $120 million. The disease, caused by the soilborne fungus, Sclerotinia sclerotiorum, is most prevalent in dense canopies when cool to moderate maximum daily temperatures and moisture from rain, fog, dew or high relative humidity occur during beginning flowering through early pod growth stages. 

What’s more, many of the production practices adopted to maximize overall soybean yield, such as early planting, narrow row widths, high plant populations and high soil fertility, tend to favor a dense canopy and subsequently, conditions that favor white mold. Even when farmers adopt all recommended management strategies, yield loss can still occur in years that promote disease.

“The periodic nature of white mold suggests that a fungicide applied only in those years when disease is favored should be economical and highly effective,” says Angie Peltier, University of Minnesota Extension crops regional educator. “However, significant yield losses can occur even when fungicides are timed perfectly. This is likely due to inadequate canopy penetration and coverage of the plant by the fungicide.”

With funding from the Minnesota Soybean Research & Promotion Council, Peltier is testing a new approach to manage white mold in Minnesota soybeans. 

“A radical improvement in canopy penetration and coverage of fungicides has the potential to be a game-changer when it comes to in-season white mold management,” she says. 

In 2020, Peltier conducted irrigated, inoculated field trials to compare coverage and efficacy of fungicides applied between rows and within the canopy to the typical above-the-canopy application. Plots were also assessed for disease incidence and severity, yield and moisture.

To collect fungicide coverage data, water-sensitive paper was placed six and 12 inches above the soil line within rows. When plants reached beginning to full flowering, Endura was applied either over the top or within the canopy. Plots were then infested with the fungus and irrigated to improve the chance of disease development. Software was used to estimate spray coverage. Ultimately, within-the-canopy application resulted in significantly better fungicide coverage than the over-the-top application at both six and 12 inches above the soil line. 

“The 2020 work provided some evidence of improved fungicide coverage and deposition within the canopy. But, hot weather prevailed after the treatments were applied and we were unable to determine how the system might affect fungicide efficacy,” she says. “The work is being repeated this year.”

Peltier continues to stress that an integrated white mold management strategy is best. Soybean farmers with a field history of severe white mold are encouraged to plant partially resistant soybean varieties at the lowest recommended seeding rate into fields where non-host crops such as corn, wheat, rye or oats have been grown for two or three years. During the growing season, the smartphone app Sporecaster can help farmers understand each field’s risk of white mold. Sporebuster can help farmers decide whether fungicides make economic sense for their farms.

“If this technology is found to significantly improve fungicide efficacy in protecting the soybean crop against white mold, the next step will be to test older, currently less effective fungicides that are no longer under patent protection to see whether better covering the site of infection can improve the efficacy of those fungicides,” she says. 

Published: Aug 16, 2021