Annual broadleaf weeds hurt Nebraska's winter wheat crop by competing for water, light, space, and nutrients, which reduces yields by an estimated 10% each year, says Steve Young, UNL Extension weed ecologist at the West Central Research and Extension Center in North Platte.
Weeds also slow harvest and increase combine repair costs, he says, adding that producers may be docked at the elevator for excessive grain moisture and/or weed seeds in wheat.
The effectiveness of post-harvest weed control is influenced by production practices associated with the previous wheat crop, such as winter wheat variety selection, fertilizer practices, row spacing, planting date, and seeding rate.
Other factors influencing weed control include
•cutting off weed tops with the combine;
•temperature when spraying;
•rain the day of spraying;
•streaks caused by sprayers;
•dust, straw, and chaff; and
•weed seed distribution.
Less residue from a winter wheat crop also will make the next crop less competitive with weeds. Weeds under stress are very difficult to control, according to Young. Each field should be examined separately. The key is to prevent weeds from using soil water and producing seeds.
Success with reduced and no-till programs is improved when winter wheat stubble remains weed-free after harvest, he says.
"Allowing weeds to go to seed will cause problems in future crops. These potential problems underscore the importance of broadleaf weed control in winter wheat. An effective weed control program considers the entire cropping system. This approach involves the use of preventive, cultural, and chemical weed control methods."