From Joaquin Navas (Exaltar, Guatemala):
We planted on May 10th and the plants have developed very well. However, the last 3-4 weeks have been very rainy and we observed a white fungus growing on some of the plants. We identified it as Sclerotinia sclerotiorum and estimated that less than 5% of the plants have been affected by the fungus. We learned that this fungus has also been found in neighboring fields of beans, so we assume that it was in the soil.
Our main concern is about handling and using the soybeans that we will be harvesting in a couple of months' time. Should we discard all the soybeans from plants affected by the fungus even if the pods look fine? Can the fungus be transmitted through the seeds, and if so, what would be the appropriate way to manage/use the beans once they are harvested? Any other comments or advice will be greatly appreciated.
Amado was correct - you have a disease that is commonly referred to as white mold or Sclerotinia stem rot which is caused by Sclerotinia sclerotiorum. You can see the actual fungus on the stem - the white mycelia and the black, round sclerotia sitting on top of the mycelia - as well as the bleaching and rotting of the stem that is caused by the fungus.
It is a fairly common disease and often occurs wherever soybeans are grown in cooler and wetter environments. It is also a problem on beans and sunflowers, but not maize.
Often times crop rotation does not effectively work because of the broad host range of the fungus and the long lasting survival of the sclerotia. Using Trichoderma could help in reducing the disease but may not eliminate it.
I would discard those soybean plants that have symptoms (rogue them out before harvest) and then I would carefully sort out the seeds from the remaining plots discarding any debris and any discolored seeds. The fungus can be transmitted via seed or debris in seed lots.