Herbicidal Activity of Brassicaceae Seed Meal on Wild Oat (Avena fatua), Italian Ryegrass (Lolium multiflorum), Redroot Pigweed (Amaranthus retroflexus), and Prickly Lettuce (Lactuca serriola)

The need for sustainable agricultural-production systems has generated demand for effective, nonsynthetic, alternative weed-control strategies. For some vegetable crops there are few herbicide options available, and there is little prospect of new herbicides being registered for vegetable crops. Brassicaceae seed meal, a residue product of the seed oil extraction process, can provide a resource for supplemental nutrients, disease control, and weed suppression. The objective of this study was to evaluate the effect of different Brassicaceae seed meals and application rates on the emergence of wild oat, Italian ryegrass, prickly lettuce, and redroot pigweed, which are some of the major weeds in vegetable production systems. White mustard seed, Indian mustard seed, and rapeseed meals were used with (intact) or without a functional myrosinase enzyme (denatured). Intact white mustard seed meals applied at a rate of 2000 kg ha(-1) significantly reduced weed seedling emergence and weed dry biomass compared with intact rapeseed-meal amended treatments. Indian mustard showed significantly better herbicidal efficacy on the grassy weeds than did white mustard, which was most effective in controlling broadleaf weeds. In all instances, a 1000 kg ha(-1) application rate of either Indian mustard or white mustard exhibited greater herbicidal effect than did the 2000 kg ha(-1) application rate of rapeseed meal. These results demonstrate that all glucosinolates are not equal in herbicidal effects. The herbicidal effects of the mustard seed meal could offer vegetable growers a new option for weed control, particularly in organic production systems. In practice, it would seem feasible to treat soils with a blend of Indian mustard and white mustard seed meals so that both grass and broadleaf weeds could be effectively controlled.