Effects of chemical and biological treatments on growth and yield of apple trees planted in Phytophthora cactorum infested soil

A field trial that simulated apple orchard conditions was conducted during 1994-1999 to determine the effects of metam sodium, acetic acid, neem oil, and strain EBW-4 of Bacillus subtilis Ehrenberg, Cohn on growth, fruit production, and crown and root rot ratings of cv. Jonagold apple trees (Malus domestica Borkh.) on M.26 rootstock planted in Phytophthora a cactorum (Lebert & Cohn) J. Schroet. infested soil. The drenching of soil with metam sodium and acetic acid at low and high rates, and the application of B. subtilis strain EBW-4 increased tree growth by 48-163% and fruit yield by 52-114%, and reduced the crown and root rot ratings by 36-54% compared to the untreated control. Neem oil was generally ineffective compared to the untreated controls for all of the parameters measured, except for fruit yield, which was higher in the higher-rate neem treatment in 1997 and 1999. The applications of acetic acid and B. subtilis (EBW-4) as preplanting drench applications could provide an alternative to soil fumigation with metam sodium in apple orchards affected by phytophthora crown and root rot disease or apple replant disease.