KOCHIA (KOCHIA-SCOPARIA) AND GREEN FOXTAIL (SETARIA-VIRIDIS) INTERFERENCE IN SUGAR-BEETS (BETA-VULGARIS)

Two field experiments were conducted between 1990 and 1992 under sprin kler irrigation at the Research and Extension Center, Torrington, WY t o determine the influence of mixed densities and durations of kochia a nd green foxtail interference in sugarbeet. Sugarbeet root yield and t op weight generally decreased as densities of green foxtail and kochia increased whether alone or in combination. Reductions in sugarbeet ro ot yield and above ground biomass from mixed densities of kochia and g reen foxtail were additive at the low and intermediate density but les s than additive at the high density of either species. Sugarbeet root yield decreased as the duration of interference after sugarbeet emerge nce from a mixed density of kochia and green foxtail increased. Since sugarbeet plants were irrigated to avoid water stress and adequate nut rients were applied, it appears that kochia and green foxtail interfer ed with sugarbeet primarily for light, based on light and height measu rements. Season-long as well as duration of interference did not show any significant effect on sucrose content. Based on regression analysi s the lowest densities of kochia and green foxtail required to reduce root yield were approximately 0.3 and 0.06 plants/m of row, respective ly. The minimum duration of time that 0.5 kochia and 3.0 green foxtail plants/m of row can interfere with sugarbeets before root yield is ec onomically reduced was approximately 3.5 wk after sugarbeet emergence.