ARS | Publication request: WEED SUPPRESSION WITH BRASSICA GREEN MANURE CROPS IN GREEN PEA

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 1997
Publication Date: August 1, 1997
Citation: AL-KHATIB, K., LIBBEY, C., BOYDSTON, R.A. WEED SUPPRESSION WITH BRASSICA GREEN MANURE CROPS IN GREEN PEA. WEED SCIENCE. 45:439-445. 1997.

Interpretive Summary: Weed control in green peas is mainly accomplished with herbicides. Fall- planted Brassica species (rapeseed and white mustard) can suppress weeds, nematodes, insects, and diseases in crop rotations. Pest suppression is often attributed to decomposition products of the Brassica cover crop, which include istothiocyanates. In these studies, fall-planted green manure crops of wheat, rye, white mustard, and rapeseed were tested for weed suppression in peas planted the following spring. Wheat suppressed weeds in green peas the least, whereas rapeseed suppressed weeds in green peas the greatest. However, rapeseed also reduced pea stand. Weeds were suppressed early in the spring by fall-planted cover crops, but without a cultivation or herbicide treatment the weeds were competitive with the pea crop and reduced pea yields. Growers can utilize fall-planted cover crops to suppress early season weed growth as part of an integrated weed management program.

Technical Abstract: Weed suppression in green pea was evaluated when green pea was planted after a fall planting of rapeseed, white mustard, rye or wheat had been incorporated in the soil in spring. Tests were conducted at Mount Vernon, WA, in 1994 and 1995. Weed suppression in peas varied between different green manure crops. One month after planting, the highest weed population was in green pea following wheat, where as the lowest was in green pea following rapeseed. Rye and white mustard suppressed early weeds relative to wheat by 25 and 30%, respectively. However, at harvest, weed density was similar in green pea planted after all green manure crops. Weed suppression improved when cultivation or metribuzin at 0.14 kg ha-1 was used in combination with white mustard, rapeseed, or rye. Pea population was not affected by green manure crops, except for rapeseed, which reduced pea population. In green house experiments, white mustard added to the soil at 20 g per 400 g air-dry soil reduced emergence of shepherd's purse, kochia, and green foxtail by 97, 54, and 49% respectively. Rapeseed suppressed emergence of shepherd's purse, kochia, and green foxtail by 76, 25, and 25% respectively.