By Darren Hefty

Sclerotinia white mold is a disease that affects broadleaf crops in the Upper Midwest like sunflowers, soybeans, dry beans, canola, and others.  It is caused by a fungus and varies in severity from year to year based on favorable weather conditions and the presence of a susceptible host.

Why Was White Mold a Problem in 2015?

2015 was a good year for white mold because the cool and wet weather we had during the reproductive growth stages set the stage for this disease and others.

Let me give you an example from a soybean field in western Minnesota. The time when soybeans are most susceptible to white mold is during the reproductive stages of growth that occur after June 21st when the day length begins to shorten.  When flowers dry up, the white mold has a path of entry into the plant.  This year, western Minnesota was cool and relatively wet through early July when soybeans were flowering.  Eight of the first ten days of July had nighttime lows in the 50s, with July 8 showing an overnight low of 49 degrees.  Daytime highs were in the low to mid 70s with a few days reaching the lower 80s.  Add to that 4.5 inches of rain in June and five rainfall events in July, and you have perfect conditions for white mold development.

Managing Fields for White Mold

White mold is a fungal disease, and there are some proven management strategies.  Using soybeans as an example, see these five points below.

  1. If you had white mold this year, consider applying Contans to those fields this fall.  Contans is a naturally occurring fungus (Coniothyrium minitans) that attacks and destroys the sclerotia that are left in your field after a white mold infestation.  Contans can be applied either in the fall or spring, but we prefer to get it out there as soon as you can to allow more time for it to work prior to planting a susceptible crop.
  2. Crop rotation – Rotating to a non-susceptible host like corn eliminates the risk of white mold that year and reduces your risk in future years.
  3. Varietal selection – Varietal selection can help, but it is not the total answer.  There is a difference in tolerance between varieties, but there are no resistant varieties.  That said, picking a tolerant variety with more of a slender, upright frame is a plus.
  4. Cultural practices – Deep tillage, wider row spacings, and lower plant populations can all help reduce the severity of a white mold outbreak.
  5. Foliar fungicides – There is a big difference in which fungicide you choose as some like Headline offer little protection from white mold.  Endura, Proline, and Domark are examples of products that have white mold activity, with Endura being the strongest and most expensive of the options listed.  Target applications to occur just as the reproductive stages begin and then again ten days to two weeks later.  A third application may be needed in extreme cases.  Timings may vary slightly depending on the crop you’re protecting.  Keep in mind fungicides work best when applied BEFORE there is disease present.

2016 may again be a big year for white mold in multiple crops, but proactively managing your land for white mold can really help.