Effects of green manure type and amendment rate on Verticillium wilt severity and yield of Russet Burbank potato

Increasing restriction of agrochemicals is motivating development of ecology-based cropping systems, including green manures, to manage soilborne diseases. Green manures have shown promise in suppressing Verticillium dahliae, but information about effect of different green manures and optimal application rates remains limited. Therefore, we conducted two single-year field experiments comparing effects of Austrian winter pea (Pisum sativum 'Melrose'), broccoli (Brassica oleracea var. botrytis 'Excelsior'), and Sudan grass (Sorghum vulgare var. sudanense 'Monarch'), amended at 6, 12, or 24 Mg ha(-1), on soil populations and root infection by V dahliae, wilt severity, and yield of Russet Burbank potato. Inoculum density was reduced relative to the nonamended, infested control by all broccoli treatments, Austrian winter pea applied at 12 and 24 Mg ha(-1), and Sudan grass applied at 12 Mg ha(-1). Root infection was not reduced by any green manure treatment. Median wilt severity was reduced approximately 70% by all green manures applied at 24 Mg ha(-1) and 74% by Austrian winter pea applied at 12 Mg ha(-1). Tuber yield was reduced approximately 20% in nonamended, V dahliae-infested controls relative to the noninfested controls. No green manure treatment improved yield relative to the nonamended, infested control.