Limiting green and yellow foxtail (Setaria viridis and S-glauca) seed production following spring wheat (Triticum aestivum) harvest

Green and yellow foxtail seed production following harvest of spring wheat is a concern of producers in the northern Great Plains of the United States and the Prairie Provinces of Canada. Experiments were conducted in 1996 an d 1997 in three tillage systems, no till (NT), chisel plow (CP), and moldbo ard plow (MP), at the University of Minnesota West Central Experiment Stati on, Morris, MN, to determine whether time of glyphosate application or till age after spring wheat harvest could reduce postharvest foxtail seed produc tion. In both years, hard red spring wheat was planted in late April and a packaged mixture of fenoxaprop and 2,4-D ester and MCPA ester was applied a t a rate of 53 g and 81 g and 246 g ai/ha for grass and broadleaf weed cont rol. Following spring wheat harvest, each main plot was subdivided into sev en subplots, including an untreated control. One subplot was disked twice a t 4 to 6 d after harvest (DAH) of spring wheat, and five other subplots had glyphosate (0.25 kg ai/ ha) applied on different days (1 to 31 DAH). Foxta il seeds were collected from the soil surface following first frost, and th e number of green and yellow foxtail seeds were determined. Tillage immedia tely after spring wheat harvest eliminated foxtail plants, and no new foxta il seedlings emerged in either tilled or glyphosate-treated plots despite i deal postharvest conditions for foxtail germination and emergence in 1997. Most viable green foxtail seeds were consistently obtained in NT plots, whe reas yellow foxtail seed production varied among tillage systems. Either ti llage soon after spring wheat harvest or glyphosate application within 16 D AH reduced green and yellow foxtail seed production by greater than 70%.