Last week we discussed Sudden Death Syndrome, so this week I decided to continue talking about problems that farmers face with a soybean crop. On Sunday, we drove past a few fields on the way to church that have been hit by what’s called white mold. Once we changed into more field appropriate clothing, dad went with me to a neighbor’s farm to get a closer look at the sick plants.

This spring and summer were particularly cool. Although we had some dry spells, it was also wet or damp. As you can imagine, just like other molds, white mold tends to favor those conditions. The mold, which officially is called Sclerotinia stem rot, thrives in cool damp fields. The symptoms from the mold usually show up in July and August. The disease will start with just a single plant here and there where the leaves will wilt and die. Eventually, the entire plant will die.

As you can see from the photos, a bean crop tend to create somewhat of a canopy with their leaves. Beneath the leaves, where it is protected and shaded by the sun, it can remain damp. Again, it creates a favorable environment for the mold.

Although it is a little hard to see on the above picture, there are actually “clumps” of white stuff on the stem of the dead plant. As you can imagine, the mold can really hit yields. Once the plant dies, it isn’t going to allow the soybeans to fully mature and (obviously) it won’t create any new ones.

Currently, the best management for the mold is just stopping it from getting into the field in the first place. In fact, farmers are usually advised not to harvest a field containing white mold before harvesting a field that does not have it. The spores can actually get on the equipment and be transferred from one field to the next.

Some seed companies promote bean varieties that are better equipped to resist the mold, but there are currently no beans available that are completely resistant to it. There are also some fungicides that are available, but won’t necessarily control all of it or eliminate it from the field.

The other difficulty is that some methods for increasing soybean yields can also be a boost to the mold. For example, although planting in narrow rows with high seed populations can increase yields for soybeans, such planting methods also increase the likelihood that the mold will spread. The more soybeans that are planted closer together, the thicker the canopy will be.

Further, the mold can live in the soil for up to 10 years, so crop rotation does not necessarily help unless farmers can keep that land productive in other crops for a decade. Many types of weeds are also good hosts for white mold and can spread the spores even when soybeans aren’t planted in the fields. However, rotating with plants that are not susceptible to the mold can at least help cut down on the number of mold spores in the field and reduce future incidents in soybeans.

If you’d like to learn more about white mold, check out my sources at Purdue Extension, Pioneer, and Crop Production Services.