EVALUATION OF COMMERCIALLY AVAILABLE PHOSPHONATE PRODUCTS FOR CONTROL OF Phytophthora cinnamomi

There are numerous phosphorous acid products on the market that are sold as fertilizers but can have the same effect as a phosphonate fungicide on avocado root rot. Six different products, which were sold as either buffered fungicides or fertilizers, were tested for their efficacy against Phytophthora cinnamomi using avocado ‘Topa Topa ’ seedlings planted in 5 X 15 cm liners with an organic potting mix. Products were applied as a drench equivalent to 2 liters of active phosphonate per hectare. One product was applied twice during the trials. The experiment included non-inoculated, as well as inoculated controls. There were 20 replications of each treatment. After disease progression had occurred the plants were separated into root and shoot portions, weighed, dried and reweighed. The trial was repeated two times. There were no differences in the efficacy of any of the materials, nor in single versus double applications. Trees treated with phosphonate had significantly greater root weights than untreated, inoculated trees, but less than untreated and uninoculated trees