Several postemergent herbicides can control quackgrass in broadleaf crops. The main advantage of using in-crop herbicides is that quackgrass may be suppressed while spraying for annual grass weeds and volunteer cereals. Roundup applied in the fall or in the spring before planting may give more consistent control of quackgrass than any of the postemergent grass herbicides. Several factors can influence the effectiveness of quackgrass control with Roundup. The stage of plant growth, the vigour of the plant, air temperature and frost each play an important role in quackgrass control.
Tillage can also be a factor.
During a study at Agriculture and Agri-Food Canada's research station at Lacombe, Alberta, quackgrass was consistently controlled better with herbicides under conventional tillage than zero tillage. This does not imply that quackgrass cannot be controlled under zero tillage systems. However, it emphasizes that quackgrass control in zero tillage systems requires careful management of herbicide applications. Other findings at Lacombe indicated that Roundup applied in the fall and again the following spring can reduce the viability of quackgrass rhizome buds under both conventional and zero tillage systems. Quackgrass Control Checklist Treat quackgrass at the 3 to 4 leaf stage for consistent control.