The Disease Triangle to Avoid

Mar 29, 2023

The uncontrollable factor in fighting white mold is the weather.
The combination of 1) healthy soybean plants, 2) cool, wet weather, and 3) a fungus called sclerotinia sclerotiorum forms a “triangle” of environmental conditions ripe for yield-robbing, crop damaging white mold.
How can you avoid the white mold disease triangle?
First, “you can’t manage the environment [the weather],” said Rod Gustafson, Federated’s Albertville location manager. There’s no controlling the temperature, rain, or humidity that breeds this devastating fungus.
Secondly, you can’t control the presence of the white mold pathogen/fungus. “It’s either there or it’s not,” Gustafson said. You can treat the soil with Contans® in the fall to minimize the sclerotia seeds (they look like rat droppings) for the next season, but this option is generally reserved for only the most problematic fields.
The third leg of the triangle, however, is under your control.
You can manage the susceptibility of your soybeans by planting varieties that are more tolerant to white mold. Federated offers several such varieties.
You can apply seed treatment to those varieties to help build the plant’s mechanism to resist white mold. Federated recommends Heads Up® [brand] seed treatment “for not that big of a cost,” said Gustafson. (This brochure offers more info on Heads Up, a product also effective against Sudden Death Syndrome.)
You can follow “good cultural practices,” he said: Keep seed population under 140,000 seeds/ac. and maintain 30-inch row spacing to keep the canopy open longer into the season. “More plants per acre doesn’t always translate into higher yields,” he said, especially if white mold becomes an issue.
You can apply a fungicide at R1, once the beans start flowering. “R1-R2 is really when you need to spray,” Gustafson said, stressing that “timing is everything” for managing white mold.
If the triangle closes in on your soybean crop, mitigate conditions as best possible for the upcoming season. Start by ensuring that you don’t spread the fungus via the combine at harvest. Clean the machine between fields and harvest fields with white mold last.
“You also might need to plant corn for two or three years,” said Gustafson. While breaking the corn-soybean rotation isn’t a permanent fix, it can reduce the rate of survival for the fungus.
Talk to your Federated Agronomist now to get the best varieties, seed treatments, and fungicide for this year’s soybean crop.

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