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How to Manage Pests
UC Pest Management Guidelines
Alfalfa
Rhizoctonia Root Canker
Pathogen: Rhizoctonia solani
(Reviewed 11/06,
updated 11/06)
In this Guideline:
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Tan, elliptical lesions on the taproot in the areas where lateral
roots emerge are distinctive symptoms of Rhizoctonia-related diseases. In winter when the fungus is inactive,
these sunken lesions will turn black and appear to be inactive. If roots are
girdled during summer, the plant will die. If infection is not severe, new
roots will emerge when temperatures are too cool for the fungus.
Rhizoctonia root canker, also known as crown and stem rot, occurs
during periods of high temperatures and high soil moisture. The fungus occurs worldwide and also
causes serious seedling damping off; however in California, most new stands are
planted when temperatures are less than ideal for disease development. The disease is mainly found in the low
desert valleys of Palo Verde, Imperial, and Coachella. Only certain strains of
the fungus can cause the root canker form of disease. No control measures are known
for these diseases.
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UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430
Diseases
R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County
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