Herbicidal activity of mustard seed meal (Sinapis alba ‘IdaGold’ and Brassica juncea ‘Pacific Gold’) on weed emergence

• Herbicidal activity of two mustard seed meal were determined in three experiments.
• Sinapis alba ‘IdaGold’ and Brassica juncea ‘Pacific Gold’ were used.
• Herbicidal efficacy varied with type of mustard seed meal and weed species.
• Herbicidal efficacy varied with application rate and method.
• Surface application may be more effective than substrate incorporation.

Mustard seed meals (MSMs) are by-products resulting from crushing mustard seeds to provide biofuel. MSMs have been applied as bio-herbicides due to the release of active glucosinolates hydrolysis products. Three experiments were conducted to determine the herbicidal activity of MSM (Sinapis alba ‘IdaGold’ and Brassica juncea ‘Pacific Gold’) in two weed species, large crabgrass (Digitaria sanguinalis) and Palmer amaranth (Amaranthus palmeri). In petri dishes, MSMs were applied at 0, 50, 100, 200 or 300 g/m2. In greenhouse containers, MSMs were applied on the surface or incorporated with germination mix at 0, 1.5, 3.0 or 4.5 g/pot. In outdoor containers, MSMs were incorporated with germination mix at 0, 1.5 or 3.0 g/pot. In petri dishes, emergence percentage (EP) and emergence index (EI) of large crabgrass were lower in ‘Pacific Gold’ than ‘IdaGold’ under unsealed conditions, and EP and EI were lower under sealed than unsealed conditions at all rates. In greenhouse containers, the EP and EI of crabgrass were lower in ‘Pacific Gold’ than ‘IdaGold’ when applied on the surface at 3.0 and 4.5 g/pot, while EP and EI was lower in ‘Pacific Gold’ when applied at 1.5 to 4.5 g/pot under both two methods. The EP of amaranth was lower in ‘IdaGold’ than ‘Pacific Gold’ at 1.5 g/pot under both methods, while EI was lower in ‘Pacific Gold’ when applied on the surface than incorporated. In outdoor containers, EP and EI of crabgrass were lower in ‘Pacific Gold’ than ‘IdaGold’ at 3.0 g/pot. These results demonstrated that ‘IdaGold’ might have better herbicidal efficacy on Palmer amaranth (broadleaf weeds), whereas ‘Pacific Gold’ was more effective on large crabgrass (grass weeds).