WEED SUPPRESSION WITH BRASSICA GREEN MANURE CROPS IN GREEN PEA

Weed suppression in green pea was evaluated when green pea was planted after a fall planting of rapeseed, white mustard, rye, or wheat had b een incorporated into the soil in spring. Tests were conducted at Moun t Vernon, WA, in 1994 and 1995. Weed suppression in peas varied betwee n different green manure crops. One month after planting, the highest weed population was in green pea following wheat, whereas the lowest w as in green pea following rapeseed. Rye and white mustard suppressed e arly 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 metribuzi n at 0.14 kg ha(-1) was used in combination with white mustard, rapese ed, or rye. Pea population was not affected by green manure crops, exc ept for rapeseed, which reduced pea population. In greenhouse experime nts, white mustard added to the soil at 20 g per 400 g air dry soil re duced emergence of shepherd's-purse, kochia, and green foxtail by 97, 54, and 43%, respectively. Rapeseed suppressed emergence of shepherd's -purse, kochia, and green foxtail by 76, 25, and 25%, respectively.