Biological and chemical treatments for control of phytophthora crown and root rot caused byPhytophthora cactorumin a high density apple orchard

Twenty-one strains of Bacillus subtilis, one strain of Enterobacter aerogenes, metalaxyl applied as a soil and trunk drench, and monoammonium phosphate applied as a broadcast treatment, were evaluated for 8 years at Creston in the Kootenay Valley of British Columbia in inoculated high density apple tree plantings for control of phytophthora crown and root rot caused by Phytophthora cactorum. Metalaxyl controlled the disease completely for 8 years. Monoammonium phosphate and strain B8 of E. aerogenes significantly reduced the number of trees infected with P cactorum compared with the control. Strains AB8. BACT X, NZBI, AB7, AB8, and BACT 2 of B. subtilis significantly reduced the number of trees infected by P cactorum and increased the trunk diameter compared with the control. The level of protection provided by these bacterial antagonists under field conditions suggests that they could provide biological control of phytophthora crown and root rot of apple trees in the field in the Kootenay Valley of British Columbia.