White Mold in Soybeans

The past few weeks we have been noticing and have fielded the odd call about some white mold issue in the countryside.  White mold infection process begins with the black bodies (sclerotinia, above) that grow from previous infections in past years that have been re-deposited to the soil.  The sclerotinia over-winter like seeds that germinate a small mushroom-like structure (right) called and apothecia, which releases millions of infecting spores.  In order for these spores to infect, dead plant material must be present for the spores to colonize and eventually move to the living material.  Killing stems and choking the flow of water and nutrients to the rest of the plant. 

As you might have noticed, this year is the year we would be seeing many disease issues, as it has been quite damp, with heavy dews, plenty of rain, and moderate/below-average temperatures.   These are the types of conditions that fuel this disease, as well as a few other factors:

·         A dense canopy that does not allow for good airflow.  Minimizing dampness in the canopy minimizes infection; white mold spores need moisture to take hold. 

·         Conventionally tilled/minimally tilled fields.  Tilling soil burries the sclerotinia, allowing for better germination of apothecia.  If you no-till, the sclerotinia are left on the surface with little seed-soil contact and are left exposed to the elements, as well as germinate and release spores in a crop that is not susceptible (ie corn, wheat).  Rotation will help plenty as well.

·         Highly growthy areas, particularly loams and muck soils.

·         A susceptible variety planted in prone areas is also a factor. 

What I would consider the most though if you have a highly susceptible farm is to grow a highly resistant variety.  In our maturity zone, Pioneer has one variety that his highly resistant (P22T69R), one that is moderately resistant (92Y55), a few that are average, and a few that are susceptible.  On the right is a picture taken last week in our own soybean plot (planted in a mucky area of one of our farms) with P22T69R, a highly resistant line on the left, and P24T19R, a susceptible line on the right.  If you know you have mold problems, P22T69R is the bean to grow on that farm!