White Mold Affecting Local Soybeans
This is not what you want to see in your bean field late in the season, As beans mature the leaves normally go from green to yellow to brown and then fall to the ground. Bean leaves should not go from green to black as you can see in large areas of this bean field. This is a picture of a bean field I drive by on my way out to the farm. I do not know whose it is but I am thankful it is not mine.
I saw these areas begin to die a few weeks ago. I did not walk into the field because it was not mine but I am pretty sure I know why those big areas died a few weeks ago. All the rain and high humidity have been the ideal weather for white mold. White mold can survive in the soil for many years in structures called sclerotia. They look a lot like mouse droppings.
When there is a lot of rain with high humidity the sclerotia begin to grow under the bean canopy and infect the beans when they are flowering. Then later on in the season, the mold covers a portion of the bean stem and the plant dies. Some soybean varieties have more tolerance to white mold so variety selection is important. Planting in wider row spacing and lower populations also reduce the severity of white mold.