Effect of Seeding Dates and Densities of Green Foxtail (Setaria viridis) on the Growth and Productivity of Spring Wheat (Triticum aestivum)

Competition of green foxtail [Setaria viridis (L.) Beauv.] was studied in a semi-dwarf wheat (Triticum aestivum L. ‘Norquay’) and in two normal-height wheats (‘Napayo’ and ‘Sinton’) from 1975 through 1978. Green foxtail suppressed wheat growth as well as grain yield. Tiller number, leaf area, and dry weight of wheat were reduced. Green foxtail was more competitive in the semi-dwarf variety than in either normal height variety. The intensity of green foxtail competition could not be determined by density alone. In 1975, as few as 100 green foxtail plants/m2 significantly reduced yield of Napayo and Norquay wheat by 21 and 44%, respectively. In 1977, however, 1600 green foxtail plants/m2 did not reduce the yield of Sinton wheat significantly. The intensity of green foxtail competition was highly variable from one date of seeding to the next, but there was no correlation between the level of green foxtail competition and the date of seeding. Soil temperature and moisture at the time of seeding and early growth are thought to affect green foxtail competition in wheat critically.