Control of avocado white root rot by chemical treatments with fluazinam in avocado orchards

Abstract Rosellinia necatrix Prill. is the causal soil-borne agent of avocado white root rot disease. This work proposes a new method of treatment with fungicide to combat this disease, aimed to obtain a quantitative assessment of the evolution of fungal inoculum in soil samples. A total of 39 avocado trees were selected from five commercial orchards affected by R. necatrix. Root samples were collected to recover R. necatrix isolates. The fluazinam treatments were applied around each tree by soil injection, and soil samples were collected before and after each fungicide application to analyze the evolution of the fungus by qPCR. In addition, two samplings of avocado fruits during two harvesting seasons were performed to measure the chemical residues. All 24 R. necatrix isolates taken from avocado roots were pathogenic. The qPCR quantification results showed that the percentage of fungal inoculum in the soil was significantly lower after the first fluazinam treatment compared to that before any fungicide had been applied. Furthermore, soil from non-treated avocado trees did not show any significant differences in the concentration of fungal inoculum. The chemical analysis of the fruits did not show residues. These results provide growers with a new method to control this soil-borne pathogen in crops.