Phosphorous acid treatments control <i>Phytophthora</i> diseases in Australia¹

Abstract

Treatments with a partially neutralized formulation of phosphorous acid containing potassium phosphite were assessed for control of Phytophthora diseases in subtropical and temperate crops in Australia. In Queensland, trunk injections of phosphite (10% solution) controlled severe root rot ( Phytophthora cinnamomi ) of avocado trees and resulted in the recovery of trees. Single pre‐harvest sprays (2.5 kg ha ‐1 ) of phosphite controlled root and heart rot ( P. cinnamomi ) of pineapples. Foliar sprays of phosphite (64 g per tree) controlled root rot ( P. nicotianae var. parasitica ) and trunk canker ( P. citrophthora ) of mandarin trees. In Victoria, a foliar spray of phosphite (300 g ha ‐1 ) reduced root rot ( P. clandestina ) of subterranean clover and increased dry matter by 1.96 to 5.11 t ha ‐1 . Trunk injections of phosphite (10% solution) controlled trunk rot ( P. cactorum ) of peach trees and foliar sprays (10 kg ha ‐1 ) reduced severity of root rot ( P. nicotianae var. nicotianae ) of tomatoes.