Controlling White Mold

May was a wet month with frequent rains and very little drying and June is shaping up to be fairly similar. Of course, all this cool and wet weather is good for soybean growth and rows will canopy over. However, this wet and humid weather could be setting growers up for a risk of white mold.

White mold is a fungal disease that occurs infrequently and requires a unique set of conditions in order to appear. White mold is caused by Sclerotinia sclerotiorum and the disease occurs primarily in northern Illinois in cool and wet years, when humidity is high and plant canopies are dense.

The pathogen overwinters in the soil as sclerotia which germinate when the soil remains moist for several consecutive days and the soil surface is shaded. When the climate under the canopy is humid, spores of the fungus are ejected and land on flower petals, infecting the plant. The fungus becomes inactive when warm and dry so infection ceases or slows during periods of hot and dry weather during mid-to-late summer.

Control options are limited and include planting wider row spacings and lower seed populations to reduce the canopy density and improve air infiltration. Cobra^® herbicide has been shown to work sometimes and there are a few fungicides that claim some level of control.

Arysta LifeScience has released ZOLERA^® FX fungicide that shows exceedingly good levels of control of white mold, while at the same time controlling other foliar diseases.

Lynn Justesen, technical sales specialist with Arysta, explained that Arysta is introducing ZOLERA FX to the market. It contains both a triazole (tetraconazole, also known as Domark^®) and a strobilurin (fluoxastrobin). This is the same chemistry that Bayer CropScience uses in their seed treatment fungicide combinations.

Justesen said, “Tetraconazole has a label for white mold control with an application timing at R1 (flowering). Our real difference is applying ZOLERA at R1 instead of the more typical R3-stage (pod beginning/pod set). Fluoxastrobin is unique in that you can apply it early and it has both plant and soil uptake, while the tetraconazole acts as a curative. Growers need to get in front of the disease before it ever infects and not wait until later. We recognize that it is not a silver bullet and growers still need to use good management, reduce plant density and widen row spacing.”

Brent Titus, territory manager with Arysta said, “In our trials with white mold we saw 13 bushels per acre greater yield where we inoculated with white mold. But by R3, efficacy goes down since the white mold infection period is generally over. We like ZOLERA to be applied at R1 or even pre-R1 with herbicide for best control of a potential white mold outbreak.”

Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.