Improving Management and Control of Fungal Diseases Affecting Arizona Citrus

Abstract

Experiments were initiated to evaluate chemical disease management tools for Alternaria fruit rot on navel orange and Coniophora brown wood rot on lemon trees, examine the possible effect of branch diameter on development of Coniophora wood rot on lemon trees and continue evaluations of relative resistance of rootstocks to root rot and stem canker development when inoculated with P. citrophthora and P. parasitica. Rovral or Kocide did not significantly reduce the amount of Alternaria fruit rot on navel orange trees occurring in late summer and early autumn when applied during the preceding winter or spring months. Of several chemical treatments tested, only Nectec paste inhibited the development of Coniophora brown wood rot on inoculated lemon branches. The size of wood decay columns on branches 10 mm (0.5 inch) in diameter were significantly smaller than those developing on branches 50-70 mm (2.0-2.75 inches) in diameter. In extensive trials evaluating root rot caused by Phytophthora citrophthora and P. parasitica, some relatively tolerant rootstocks were found among the group of new potential rootstocks as well as currently used rootstocks such as rough lemon, C. macrophylla and Troyer citrange. C. volkameriana was relatively tolerant to the development of root rot by P. citrophthora but demonstrated variable tolerance to P. parasitica. Comprehensive evaluation of stem canker development on citrus rootstocks inoculated with P. citrophthora or P. parasitica revealed that rough lemon is usually highly susceptible to both pathogens, while C. volkameriana was at times less susceptible (more tolerant) than rough lemon to both pathogens. Some of the new potential rootstocks were highly tolerant or resistant to infection of stem tissue by P. citrophthora or P. parasitica.