Bean IPM

Legume ipmPIPE Diagnostic Series

Web Blight

Rhizoctonia solani (Thanatephorus cucumeris)

Tags
All legume crops
Symptoms

Small necrotic lesions (2-10 mm in diam) with brown centers and olive green margins form on leaves. Lesions become water-soaked, enlarge and coalesce rapidly to take on a scalded appearance, and become covered by whitish to brown mycelium, with small sclerotia.

Factors favoring
  • Presence of previously infested crop debris
  • Lack of crop rotation
  • Poor sanitation of previous legume and weed debris
  • Contaminated seed
  • Susceptible varieties
  • Moderate to high moisture conditions favor slugs
  • Infection at V2 – R2 results in plant death, and/or reduced pod set, poor seed fill, and yield loss
Decaying leaves
Symptoms of web blight (Thanatephorus cucumeris) on the foliage of dry beans.
Decaying leaves
Symptoms of web blight (Thanatephorus cucumeris) on the foliage of dry beans.
Additional Resources
Authors

H. F. Schwartz, Colorado State University and S. K. Mohan, University of Idaho

Photo credits

Howard F. Schwartz, Colorado State University, Bugwood.org