SELECTION OF HIGH YIELDING, WEED COMPETITIVE WINTER WHEAT CULTIVARS

Field experiments were conducted during the 1981-82 and 1982-83 winter wheat (Tritium aestivum L.) growing season at Lincoln and North Platte, Nebraska, U.S.A. to establish the relationship among weed competitive wheat growth parameters and dry weight of weeds. Attempts were made to identify high yielding, weed competitive winter wheat cultivars for the Central Great Plains region. Winter wheat cultivars were grown with and without downy brome (Bromus tectorum L.) in 1981-82 and the experiment was repeated in 1982-83 with the addition of field pennycress (Thlaspi arvense L.). Significant reduction in the dry matter of both weeds occurred due to high canopy diameter and tiller number of wheat. Higher canopy diameter and tiller number cultivars probably possessed more leaf area index, occupied more land space, utilized more photosynthetically active radiation (PAR), and more thoroughly shaded weeds. Continuous shading decreased photosynthetic efficiency of weeds and made them less vigorous competitors. Thus, less dry weight of weeds was observed with increasing wheat canopy diameter and tiller number. The inverse linear regression of decreasing dry weight of weeds with increasing wheat canopy diameter and tiller number was significant irrespective of the weed species, location, and growing season. Experiments under heavy weed infested plots in 1982-83 indicated the importance of each centimeter of canopy diameter and tillers of crop in assisting with weed management. Dry weight of weeds at intercept was 1 kg m(\u27-2) in each regression equation of crop parameters. Rate of decline in the dry weight of downy brome was 45 g cm(\u27-1) m(\u27-2) due to canopy diameter. Tillers reduced dry weight of downy brome by about 1 g tiller(\u27-1) m(\u27-2). Choosing cultivars based solely on the relative weed competitiveness led to the identification of some low yeilding cultivars. In order to identify high yielding, weed competitive cultivars for weed infested areas, selection should be based both on grain yield and weed competition. NE78798, SD75284, and Vona were the high yielding, weed competitive cultivars. The widely grown Centurk 78 was not high yielding under heavy weed infested areas. Therefore, NE78798, SD75284, and Vona would be acceptable culivars for weed infested areas of the Central Great Plains