Symptoms and Signs
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.
Comments on the Disease
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.