Brassica cover crops for biological weed control in no-tillage

Brassicas have high content of glucosinolates and can be used as cover crops for weed control reducing herbicide use in no-tillage. Seed germination assays were conducted in petri dishes to study allelopathic effects of rape (Brassica napus cv. “Humus”) extracts on lettuce (Lactuca sativa), redroot pigweed ( Amaranthus retroflexus) and green foxtail (Setaria viridis ). Freeze-dried rape shoot and root were extracted in water at 0 to 5% (w/v) concentrations. Increasing ITC (positive control) and rape extract concentrations reduced lettuce, pigweed and foxtail seed germination. The highest inhibition (only 100%) occurred at the 5% extraction rate. Root extract at 5% showed lettuce seed germination inhibition activity equivalent to 2.6 mM ITC.; Lettuce and “Humus” were planted together in pots at densities of 0 to 100% of total plants. Increasing rape density reduced lettuce biomass production with maximum reduction being 85% at rape density of 75%. Pigweed and foxtail were planted in pots previously grown to rape and lettuce for 40 and 90 days. Weed yield was reduced by as much as 80% when the density of rape in the pot prior to planting pigweed and foxtail was 100%. Previously untreated soil was also amended with freeze-dried rape at rates from 0 to 10 g/kg. Increasing rates of rape reduced plant biomass production by up to 80%. The use of living rape cover crop was 36 times more efficient than a one-time application of rape amendment.; Rape and mustard (Brassica nigra) cultivars were planted in the autumn of 1999 and 2000 in no-tillage fields in Wooster, OH. Pigweed and foxtail seeds were planted the next spring in the same plots to evaluate cover crop ability to control weeds. “Humus” produced biomass of 5 Mg/ha and was the best cultivar for weed control reducing foxtail biomass production by 98%. Winter rapes “Ceres” and “D. Essex” produced larger biomass when planted in August than when planted in September.; Rape “Humus” aqueous extracts reduced seed germination by allelopathy. Living rape was more efficient for weed control than soil incorporated rape. “Humus” was the best Brassica cultivar for weed control in no-tillage.