Comparative Efficacy of White Mustard (Sinapis albaL.) and Soybean (Glycine maxL. Merr.) Seed Meals as Bioherbicides in Organic Broccoli (Brassica oleraceaVar. Botrytis) and Spinach (Spinacea oleracea) Production

Abstract

White mustard and soybean seed meals were compared for weed control and yield of organically grown broccoli and spinach. The meals were incorporated into the soil 2 weeks before crop planting at two rates (1.24 and 4.48 t ha −1 ). Weed densities and hand-weeding time were recorded twice during the growing seasons and weed biomass was measured at crop harvest. Compared to the 1.24 t ha −1 soybean treatment, weed densities were 52 to 95% and 41 to 45% less at 3 and 6 weeks after planting, respectively, in both crops with the 4.48 t ha −1 white mustard seed meal treatment. Time required for hand weeding at these times was also reduced by up to 82% and 48%, respectively. Broccoli yield was similar in all the treatments, but spinach yield was greatest in the 4.48 t ha −1 treatments for both seed meals. Petiole nitrate and nutrient concentrations in both crops were generally similar in all the treatments.

Evaluating Mustard Seed Meal for Weed Suppression in Potato (Solanum tuberosum)

“…These results are in agreement with previous research where MSM at 2.2 to 4.5 MT ha -1 reduced early season weed density in field trials on onions, cucurbits, broccoli, and spinach (Boydston et al, 2011;Shrestha et al, 2015;Webber, White, Boydston, & Shrefler, 2017). The relatively poor weed suppression with DDG at 2.2 MT ha -1 is in agreement with greenhouse studies by Boydston et al (2008b) in which rates of 400 g m -2 (equivalent to 4 MT ha -1 ) or lower applied to the soil surface did not suppress weeds.…”

“…In those studies, MSM derived from Brassica juncea was more effective on grass species than S. alba MSM. Late season weed biomass, consisting mainly of barnyardgrass, was not reduced in broccoli and spinach treated with up to 4.5 MT ha -1 MSM, indicating that the weed suppressive effects of MSM did not last season-long (Shrestha et al, 2015).…”

“…Delaying planting of the crop following MSM application may reduce phytotoxicity of MSM to the crop, but would also limit the longevity of weed suppression in the crop. Transplanted broccoli and direct seeded spinach were tolerant of MSM incorporated into the soil at 1.2 and 4.5 MT ha -1 two weeks prior to planting (Shrestha, Rodriguez, Pasakdee, & Bañuelos, 2015).…”

“…Field tests of MSM in several vegetable crops have resulted in lower early season weed density, but often failed to control later emerging weeds (Boydston et al, 2011;Shrestha et al, 2015;Webber et al, 2017). In the current study, we suspect the vigorous growing potato canopy likely prevented later emerging weeds from establishing or producing considerable biomass.…”

Bioherbicides in Organic Horticulture

“…In a greenhouse study, MSM significantly decreased redroot pigweed emergence and slightly reduced total yield of onion, indicating MSM has potential to be used as a weed suppressive amendment in an organic onion production system [34]. In organically-grown broccoli and spinach, the application rate of 4.48 t/ha MSM and soybean seed meal significantly increased spinach yield, but broccoli yield was similar in all treatments [43]. However, application rates of 2.5% MSM and mustard greens seed meal significantly reduced heights and biomass in sorghum, and there was a negative effect of MSM on cotton yield [44].…”