Two field experiments were conducted between 1990 and 1992 under sprinkler irrigation at the Research and Extension Center, Torrington, WY to determine the influence of mixed densities and durations of kochia and green foxtail interference in sugarbeet. Sugarbeet root yield and top weight generally decreased as densities of green foxtail and kochia increased whether alone or in combination. Reductions in sugarbeet root yield and above ground biomass from mixed densities of kochia and green foxtail were additive at the low and intermediate density but less than additive at the high density of either species. Sugarbeet root yield decreased as the duration of interference after sugarbeet emergence from a mixed density of kochia and green foxtail increased. Since sugarbeet plants were irrigated to avoid water stress and adequate nutrients were applied, it appears that kochia and green foxtail interfered with sugarbeet primarily for light, based on light and height measurements. Season-long as well as duration of interference did not show any significant effect on sucrose content. Based on regression analysis the lowest densities of kochia and green foxtail required to reduce root yield were approximately 0.3 and 0.06 plants/m of row, respectively. 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 economically reduced was approximately 3.5 wk after sugarbeet emergence.

Two furrow irrigated field experiments were conducted for two years at the Research and Extension Center, Powell, WY to determine the influence of various mixed densities and durations of wild oat and wild mustard interference in sugarbeet. Sugarbeet root yields were reduced by competition from all examined densities of wild oat and wild mustard, alone and in combination. Root yield reduction was less than additive with mixed densities of wild oat and wild mustard. Root yields decreased as the duration of interference after sugarbeet emergence from a mixed density of wild oat and wild mustard increased. Sucrose content of sugarbeet was not altered by competition. Based on regression analysis, the minimum time that a mixed density of 0.8 wild mustard and 1 wild oat/m of row can interfere with sugarbeet before causing an economic root yield loss was approximately 1.6 weeks after sugarbeet emergence.

Wind erosion is a major problem in the establishment of sugar beets in some" areas of Wyoming as well as other parts of the Great Plains. Sugar beets are most susceptible during the establishment period when potential wind is the highest, i.e., \1ay and June. Cultural methods which leave residues on the surface appear to have the great est potential for combating this erosion problem. The objective of this study was to develop a tillage system which would protect sugar beets during their stand establishment period of growth. During the stud y comparisons of wind erosion potential, stand establishment, yield, wa ter use , and energy requirements were made between the conventional tillage practices now in use and the mulch tillage method under study. The mulch system used in this study is based on a system used in Eastern Colorado (3)'1 which employs rotary strip tillage. In this Col orado area sugar beets generally follow corn which was harvested for grain and thus there is an abundance of remaining residue for erosion protection. With preceding crops of sugar beets, potatoes, beans, or corn for silage, there is not enough remaining residue to provide erosion pro tection. Establishment ofa satisfactory mulch has thus also been a goal of this project.

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