White mold or sclerotinia stem rot
White mold is probably the soilborne disease of highest economic concern in all soybean production areas throughout NY because it is widespread and undermanaged. The pathogen survives for a very long time in the soil in the form of sclerotia, which, when conditions are favorable, will germinate to produce small mushroom like fruiting bodies called apothecia which release ascospores that are blown into the canopy and infect the soybean stems.
The disease is favored by cool temperatures with high humidity and moist soil conditions. Epidemics usually begin as canopies close and flowering begins, and may result in devastating yield losses. The pathogen has a wide host range, including sunflower, alfalfa and numerous broad-leaf weeds. However, crop rotation with non-host species, including small grains and corn, in addition to good broad-leaf weed management for 3-5 years may help to reduce the pathogen population in a field. Studies have shown that some foliar fungicides are effective at managing white mold, but timing and repeated applications may be critical and may not be cost effective.
Varietal resistance is not widely deployed as a management practice for white mold because few varieties carry even modest levels of resistance or tolerance to the disease. Cultural methods for managing the crop canopy to minimize the favorable conditions for disease development, including wider rows, row orientation and lower seeding rates have been shown to reduce the severity of white mold epidemics. Biological control with products that parasitize the sclerotia in the soil have shown limited efficacy in some research trials.
An integrated management plan which includes crop rotation, canopy management, fungicides, biological control and planting tolerant varieties is the best approach to managing white mold in NY.