White Mold In Beans
Last weekend I was pulling some waterhemp weeds in one of my bean fields when I noticed a few dead bean leaves in the canopy. Investigating further, here was one dead bean plant with white fuzz on the stem near the ground. There was no question this bean plant was killed by a disease we call White Mold. Talking with agronomists and a lot of farmers they are all seeing a lot of white mold this year.
We have had a lot of cool wet weather this summer and many mornings with a very heavy dew. That is ideal conditions for white mold to develop. The infection in this bean plant actually occurred back when it was flowering. White mold overwinters in small black sclerotia that look like mouse droppings. Spores from the sclerotia infect the bean flower. The bean plant will continue to develop normally. However, under the right weather conditions, later in the season the pathogen can kill the plant as you can see in the picture.
There is nothing you can do about white mold at this point in the growing season. While mold is a disease that we might see every few years. We do have some tools to manage it's impact. Some soybean varieties have very good tolerance to white mold while others are very susceptible. So, variety selection is important. Another management tool is to plant beans in wider rows so air can get down in the canopy and dry it off. White Mold is a fungus so it likes moisture.
Back in the 1980's there was a big shift to drilling beans in narrow rows. That worked fine until there was a year like this year and many fields were devastated by White Mold. Today most farmers plant their beans in 20 or 30 inch rows to lesson the impact of White Mold. So far I felt very fortunate because I had a scattered plant that was killed by white mold. In some fields I have seen big patches that were killed by White Mold.