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Soybean White Mold is becoming apparent in soybean fields across the Midwest
August 20, 2009
Soybean white mold (SWM) begins to show up as single plants that are wilting and dying in a generally healthy canopy. The top portion of the stem above the infection dies then dries up and the leaves remain on the stem and turn brown. A white cottony fungal growth on the stems of a soybean plant is a symptom of white mold. Another way to identify white mold is to split the stem to find black hard sclerotia that look like mouse-droppings.
Infections occur when weather conditions during the flowering stages are mild and damp. Thus, we are seeing wide spread infection this year. Last time we had significant infection was 5 years ago in 2004. Roughly there can be a .25-.5 bu/a yield reduction for each 1% plant mortality at R6-R7.
Spraying a fungicide at this time will not help. Topsin® M is the only labeled fungicide for SWM and should be applied around the R1-R2 growth stages.
While there is no way to eliminate the chance for SWM in soybeans from year to year, there are several managerial tactics that can be considered to reduce its intensity in problem fields:
• Variety Selection-no truly resistant varieties are available in the industry so select varieties with good to average
tolerance;
• Crop canopy modification-Wider rows and lower planting populations improve air movement in the canopy;
• Planting date-While early planting optimizes yields, it also results in earlier canopy closure and an increased risk of
SWM;
• Crop rotation-2 or more years of corn can lower the risk of SWM;
• Tillage- No-till or reduced tillage can reduce SWM;
• Fungicides-Contans® WG is a soil applied biofungicide that should be applied at least 6-8 weeks ahead of planting;
• Weed management-Sunflowers, pigweeds, velvetleaf, ragweed and lambsquarters are host plants so a clean field in
next year's corn crop is important;
• Cobra® herbicide application around the R1 stage has been shown to suppress SWM;
• Atrazine in the corn year has been shown to stimulate the germination of sclerotia thus potentially reducing the
amount of inoculum for future infections.