White mold is easily identified by its fluffy white spores which can be seen on the outside of soybean stems. So far, many infections are showing up in the lower canopy – a concern for growth higher up the plant.
For white mold to infect soybeans, the following conditions must be met:
The fungus must be present and actively growing in the canopy.
There must be approximately 4 to 6 hours of leaf surface moisture.
The soybeans must be flowering. (R1 to R3 stages)
The spores produced by the mushrooms will infect the flower of the soybean plant, leading to pod abortion and therefore yield damage. Typically, the lower in the canopy that flowers are infected, the more devastating the disease is to the plant above it. Fungicides can suppress infection if applied at the correct stage, between R1 (beginning flower) to R3 (beginning pod). There are several fungicide options available, consult your local chemical retailer for availability and pricing.
White mold lesions typically reveal themselves in the R4 (full pod) to R6 (full seed) stages, when the crop canopy is heavy and rain events continue. The fungus shows up especially in areas of reduced airflow, (resulting in higher crop moisture, key for infection) such as beside shelterbelts. Yield reductions can occur if enough plants are affected.
Photo Credit: Maik Kort, Lead Agronomist for Legend Seeds Canada
Knowledge Plot data from fungicide trials conducted by Legend Seeds Canada over the past three years are shown below. An average of four sites within Manitoba, the year 2013 showed positive yield improvements by applying fungicides on soybeans at approximately 5 bu/ac. 2014 and 2015 showed more moderate increases.