Bean root and stem rots are caused by fungi that live in garden soil. Rhizoctonia root and stem rot, caused by the fungus Rhizoctonia solani, is a common disease that causes reddish-brown, oval lesions (wounds) on the lower stem of the bean plant. Fusarium root rot, caused by the fungus Fusarium solani, causes a reddish-brown decay and discoloration of the roots and lower stem of the beans. Pythium root root, caused by the fungus Pythium spp., causes a wet rot of roots and stems, and white, fluffy fungal growth may be observed if moisture is high.

Select disease-resistant varieties. Avoid planting in low, poorly drained soils. Rotate beans with other crops in the garden. Avoid planting bean seeds deeply into cold soils. Plant beans once the soil has reached 69 degrees F at a 4-inch depth. Remove and destroy infected crop debris immediately after harvest.