Effect of Row Spacings and Seeding Rates of Winter Wheat on Weed Control

Field experiments were conducted during 1977 and 1978 at North Platte, Nebraska, to determine what effect row spacings and seeding rates of winter wheat (Triticum aestivum L.) had on weed control after winter wheat harvest and on corn (Zea mays L.) yield the subsequent year. Winter wheat stubble was sprayed with 1,1’-dimethyl-4,4’ –bipyridinium ion (paraquat) + 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) or N-(phosphonomethyl)glycine (glyphosate) + atrazine at 5, 25, and 45 days after winter wheat harvest. Paraquat + atrazine was also applied 270 days after winter wheat harvest. No significant differences in winter wheat grain yield existed between row spacings in either year or among seeding rates in 1977. Grain yield from the 33 kg/ha seeding rate was reduced 15% compared to the 67 and 100 kg/ha seeding rates in 1978. Winter wheat grown in 17.5 cm, as compared to 35.0 cm, rows had less weed yield and annual grass weed panicle production. In 1978 the 33 kg/ha, as compared to the 67 and 100 kg/ha, seeding rate had more weed yield and annual grass weed panicle production. The 33 kg/ha seeding rate in 17.5 cm row spacings had more winterkill in 1978, which may explain reduced grain yield and increased weed yield. Also, delaying herbicide application after winter wheat harvest, increased weed yield and panicle production. Delaying herbicide application until 270 days after winter wheat harvest reduced corn yield by 22% the subsequent year. Herbicides should be applied immediately after winter wheat harvest to prevent weeds from using soil water and nutrients and to reduce weed seed production. Advisor: Gail A. Wick