Suppression of fusarium wilt of watermelon by soil amendment with hairy vetch

Hairy vetch (Vicia villosa Roth) as a soil amendment was evaluated for suppression of Fusarium wilt of watermelon and soil populations of Fusarium oxysporum f. sp. niveum in greenhouse, microplot, and field studies. When mixed at 1 or 5% (wt/wt) in a loamy sand soil that was artificially or naturally infested with race 2 of F oxysporum f. sp. niveum, pulverized dry hairy vetch, crab shell, and urea provided the best suppression (53 to 87% reduction) of Fusarium wilt on watermelon seedlings among 13 plant and animal residues screened. Soil amended with hairy vetch at 0.25 or 0.5% (wt/wt) in microplots resulted in 54 to 69% decreased wilt incidence and 100 to 220% increase of watermelon plant biomass. Hairy vetch winter cover crop incorporated into field plots under black plastic provided 42 to 48% reduction of wilt incidence, 64 to 100% increase of plant biomass, and a 34 to 68% increase in weight of fruit, comparable to improvements achieved by the soil fumigants methyl bromide or 1,3-dichloropropene plus 35% chloropicrin. Soil amendment with hairy vetch also increased the sugar content of watermelon fruit 10 to 15%. Significant reductions in the populations of F oxysporum f. sp. niveum were not observed in hairy vetch-amended soil in microplots and field plots, but were observed in greenhouse pot soil amended with 5% (wt/wt) hairy vetch, which was attributed primarily to increased levels of fungicidal ammonia produced during decomposition. Incorporating hairy vetch into mulched soil can be an alternative or supplement to cultivar resistance and crop rotation for management of Fusarium wilt of watermelon.