Interference and Control of Wild Sunflower (Helianthus annuus L.) in Spring Wheat (Triticum aestivum L.) in Northeastern Mexico

Field studies were conducted in northeastern Mexico in 1992 and 1993 to determine the effect of wild sunflower density on its own growth and interference in spring wheat, and the effectiveness of triasulfuron and thifensulfuron on wild sunflower chemical control. Full -season interference of wild sunflower at 2, 4, 8, 16, and 32 plants/m2 decreased spring wheat grain yields by 27, 49, 60, 71 and 75%, respectively, compared to weed-free plots. Wild sunflower was more competitive with spring wheat at low densities and intraspecific interference was evident at 12 plants/m2. As a result of intraspecifíc interference, individual wild sunflower weight decreased and height increased as number of plants/m2 increased. Triasulfuron at 10.1 g/ha and thifensulfuron at 18.8 g/ha provided excellent (> 90%) wild sunflower control and adequate wheat yields. This research indicates that wild sunflower at densities as low as 1 plant/m2 reduces spring wheat grain yield signifícantly, and that both triasulfuron and thifensulfuron are good options for its chemical control.