White Mold on Soybeans: When to Treat, What to Apply

soybean field with white mold

White mold pressure is on. The weather in the last few years has produced record levels of white mold, according to John Swanson, Federated agronomist at Ogilvie. “As we are rotating back to soybeans on fields we saw white mold in 2 or 3 years ago, [growers] should consider using a foliar fungicide to reduce white mold incidence in soybeans,” he said, adding that “ it is not a 100% cure for white mold, but is an integral part of the management system.”

As they say, timing is everything. “Getting the proper timing when applying fungicides is extremely critical,” said Swanson. So, when is the best time to apply fungicides?

Most soybean plant health applications go on at R3, which is the beginning pod or ¼-inch long pod on one of the four uppermost nodes on the main stem with a fully developed leaf. However . . .

With the longest days, and thus the shortest nights, of the year occurring now, indeterminate soybeans can begin to flower. Which means, Swanson said, “if we want to make an effort to control white mold we must change our fungicide timing. As soon as we see a flower we need to be spraying.”

Scout for flowers now. “White mold fungicide applications must be put on at R1 or beginning bloom, which is one open flower at any node on the main stem. White mold spores enter the soybean plant through the senescing flowers, so it is critical to have the plant protected before the flowers begin senescing,” said Swanson.

Choose an effective fungicide. Federated recommends Aproach® fungicide for white mold. “We have seen yield increases of 9 bu./ac. or more with well-timed applications of Aproach on fields with heavy white mold pressure (see Aproach info).

Swanson said, “There are many products on the market . . . but we have had the most consistent results with Aproach.” Apply 9 oz./ac. at R1 and then follow up 14-21 days later with another 9 oz./ac. if the pressure remains high and conditions are favorable for white mold.

Talk to your Federated Agronomist about controlling white mold on soybeans before the application window closes.