Promotion of apple tree growth and fruit production by the EBW-4 strain of Bacillus subtilis in apple replant disease soil.

A field trial was conducted near Kelowna, British Columbia, to determine the effect of biological treatments alone and in combination with formalin fumigation in apple replant disease soil. The response was measured by the increase in cross-sectional trunk area, total shoot growth, and fruit yield of McIntosh apple trees on M.26 rootstock. The postplanting drench application of strain EBW-4 of Bacillus subtilis alone was consistently effective in increasing cross-sectional trunk area for 5 years, total shoot growth for 4 years, and fruit yield for 3 years. The biological agent EBW-4 of B. subtilis in combination with formalin fumigation was also effective in promoting total shoot growth and cross-sectional trunk area. The application of formalin fumigation alone was effective in increasing shoot growth for 2 years and cross-sectional trunk area for 1 year only. This treatment did not increase fruit yield for 3 years. The consistent performance of strain EBW-4 of B. subtilis during 1986-1991 indicates that this bacterium has the potential for biological control of replant disease under orchard conditions in the Okanagan Valley of British Columbia.