POTASSIUM PHOSPHONATE CONTROLS ROOT-ROT OF XANTHORRHEA-AUSTRALIS AND XANTHORRHEA-MINOR CAUSED BY PHYTOPHTHORA-CINNAMOMI

Soil drenches and foliar sprays of potassium phosphonate protected gla sshouse-grown Xanthorrhoea minor and X. australis against root rot cau sed by Phytophthora cinnamomi. Three concentrations of potassium phosp honate (0.1, 1.0 and 5.0 mg/mL), applied by both methods, reduced the severity of root rot symptoms and increased plant survival rates. Soil drenches were more effective than foliar sprays. The highest rate of foliar spray (5.0 mg/mL) was phytotoxic to both species, causing burni ng of leaf tips.