Only seven known avocado root rot infestations have been located out of the 450 acres of avocados grown in Riverside County, and of these, only one grove has been extensively damaged. As previously reported from preliminary results of the statewide survey, this Riverside study also showed that root rot damage is dependent on the introduction of the fungus P. cinna-momi in soils with poor internal drainage. However, even with the best soils, the rate of spread can be increased with excessive soil moisture.

William Thorn, John Mircetich, and Saburo Hashimoto, laboratory technicians, Department of Plant Pathology, U.C., Riverside, assisted with this survey.