No abstract

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.

No abstract

The effect of ammonium nitrate broadcast as a soil or through irrigation, urea applied as a foliar spray, and monoammonium phosphate applied as a planting hole treatment on the incidence of Phytophthora crown and root rot of apple trees was determined under orchard conditions in the Okanagan Valley of British Columbia, Canada. Results from the eight year study showed that ammonium nitrate applied as a single dose in spring at 240 g tree -1 year -1, as a split dose at 120 g tree -~ each in spring and early autumn, and in irrigation water (fertigation) at 7.5 g tree -~ wk -~ for 10 wk year -~ significantly increased Phytophthora crown and root rot of Macspur on MM106 rootstock. There was no significant difference in P. cactorum infection between the unfertilized control and treatments with urea applied as a foliar spray at 1.0 kg 1001 -~ of water in spring and early autumn, and monoammonium phosphate applied as a planting hole treatment at 1 g 1 -~ of soil at planting time.

The growth of fungi causing apple replant disease (ARD) was inhibited by the addition of N and P to the growing medium. The population of bacteria antagonistic to ARD‐causing fungi was significantly increased in the growing medium supplemented with N 400 P 400 mg/l or greater. The application of nitrogen alone or in combination with phosphorus to soil infested with fungi or bacteria that cause apple replant disease significantly increased seedling height. The addition of P alone to these infested soils did not have any effect on seedling height. Significant increases in seedling height occurred with N applications when seedlings were grown in soil to which bacteria that are antagonistic to fungi causing ARD had been added. These results suggest that the application of N, with or without P, to apple replant soils may suppress the growth of ARD‐causing fungi or bacteria and promote the growth of antagonistic bacteria.