Efficacy of white mustard and soybean meal as a bioherbicide in organic broccoli and spinach production

Authors: SHRESTHA, A - California State University; RODRIQUEZ, A - California State University; PASAKDEE, S - California State University; Banuelos, Gary

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2014
Publication Date: 2/15/2015
Citation: Shrestha, A., Rodriquez, A., Pasakdee, S., Banuelos, G.S. 2015. Efficacy of white mustard and soybean meal as a bioherbicide in organic broccoli and spinach production. Weed Science. 46:33-46.

Interpretive Summary: Weed management in organic cropping systems has often been cited as a major problem. In recent years some organic herbicides have been accepted and registered for use in these certified organic systems. Application of bioherbicides, i.e., Brassica seed material, is one area of research that has gained interest for weed management. The release of allelochemicals from Brassica seed meals has been shown to reduce the emergence of many weed species. In this two year field study, we evaluated the bioherbicidal potential of white mustard and soybean seed meal in the organic production of broccoli and spinach crops. Both meals were respectively applied at two different rates; 4.48 and 1.24 Mg/ha. Mustard seed meal was most effective in reducing total weed emergence (in both broccoli and spinach) when applied at 4.48 Mg/ha. Broccoli yields were not affected by seed meal application type or application rate, however, spinach yields were greater at the high rate of seed meal application for either seed meal type. Although, mustard meal exhibited the best potential as a bioherbicide compared to soybean meal, this treatment will need to be supplemented with other weed control methods, i.e., hand-weeding, to minimize mid-season weed competition from later-emerging weeds.

Technical Abstract: Weed control in organic cropping systems generally rely on mechanical or physical methods because of the lack of reliable organically accepted herbicides. Among the several potential bioherbicides being explored, white mustard (Sinapis alba) seed meal is among those bioherbicides that have been shown to be potentially effective against reducing the seedling emergence of certain weed species. Its efficacy has been attributed to the release of ionic thiocyanates. A two-year field study was conducted on a transition-organic field to assess the effect of white mustard and soybean seed meals on weed control and yield of broccoli and spinach. Meals were incorporated, respectively, at rates equivalent to 1.24 and 4.48 Mg/ha two weeks prior to crop planting. Total weed emergence was reduced by 52 to 95% and 44 to 45% 3 and 6 weeks after planting in broccoli and spinach, respectively, at the high mustard meal treatment compared to soybean meal treatment. Moreover, time required for hand weeding was also reduced by up to 82% and 48% in broccoli and spinach, respectively, at the high mustard seed meal treatment. Total broccoli yield was similar for all treatments, although spinach yield was greater at the high rate of seed meal application, irrespective of the seed meal type. Our results demonstrated that although white mustard seed meal treatment at 4.48 Mg/ha had the best bioherbicidal effect in the organic production of broccoli and spinach, this specific treatment will need to be supplemented with other control measures, i.e., hand-weeding, to minimize mid-season weed competition from later-emerging weeds.