Brassicaceae Cover-Crop Effects on Weed Management in Plasticulture Tomato

Weed control options are limited in plasticulture vegetables in the absence of methyl bromide. Field and laboratory studies were conducted to test the efficacy of soil amendment with Brassicaceae cover crops in combination with low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches for weed control in fresh-market tomato (Solanum lycopersicum). Three Brassicaceae cover crops, ‘Seventop’ turnip (Brassica rapa), ‘Pacific Gold’ oriental mustard (Brassica juncea), and ‘Caliente’, a blend of brown mustard (Brassica juncea) and white mustard (Sinapis alba), were tested along with methyl bromide for yellow nutsedge (Cyperus esculentus) and johnsongrass (Sorghum halepense) control in tomato. Glucosinoate (GSL) analysis indicated that ‘Caliente’ mustard, ‘Pacific Gold’ oriental mustard, and ‘Seventop’ turnip produced GSLs totaling 26,399, 16,798, and 18,847 μmol m−2, respectively, prior to termination. The VIF mulch was neither effective in increasing weed control nor in improving tomato yield over LDPE mulch. Regardless of mulch type, Brassicaceae cover crops provided marginal control of yellow nutsedge (≤39%) and johnsongrass (≤46%) at 2 weeks after transplanting (WATP). Moreover, weed control in cover-crop plots declined to ≤20% at ≥4 WATP. Soil amendment with Brassicaceae cover crops did not injure tomato plants. Although soil amendment improved weed control and marketable yield over fallow plots, none of the amended plots produced marketable yield equivalent of methyl bromide (59 t ha−1). Therefore, soil amendment with Brassicaceae cover crops cannot be used as a practical alternative to methyl bromide, but it can be combined with other strategies in an integrated pest management program.