How to Manage Pests
UC Pest Management Guidelines
Fusarium Root Rot
Fusarium root rot is characterized by brick red lesions of variable size, with diffuse margins that develop on belowground stems and tap roots. The red color gradually turns brown with age. Longitudinal fissures develop in the cortical tissue of affected areas. In severe infections, the entire root system may be attacked and destroyed. If the surface of the lesion is scraped away, small red flecks can be seen in affected tissue; this is a good diagnostic characteristic. In some plants, roots are initiated above the lesion.
The causal fungi survive for several years as chlamydospores in the soil. The disease is most commonly encountered during mid- to late season in fields with a long history of bean culture. The disease causes little damage to unstressed plants but under conditions of reduced root growth caused by drought, poor nutrition, or oxygen stress caused by wet soil, Fusarium solani is one of the causes of early maturity (aka cut out) and marked reduction in yield.
Long-term (3 years) crop rotation out of beans may reduce soil inoculum. Provide optimal growing conditions, avoiding stress caused by excess water, prolonged drought, soil compaction, etc. Although no bean line is immune, some cultivars are more tolerant to the disease than others.
UC IPM Pest Management Guidelines:
UC ANR Publication 3446
R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County