Drought, freeze, and other problems have impacted wheat stands in many areas of Kansas this year. The resulting thin stands in those areas may cause weeds to start showing up in some wheat fields — especially in fields not treated earlier. When broadleaf weeds are given the opportunity to grow rapidly in wheat fields at the end of the growing season, several potential concerns arise, including harvest difficulties, dockage problems, weed seed production, and soil water depletion. No one wants to spend extra money on a below-average crop, but it may be necessary in some cases.
Unfortunately, there aren’t many good options for pre-harvest treatments in wheat. Listed below are the various herbicide options producers can use as pre-harvest aids in wheat. There are differences in how quickly they act to control the weeds, the interval requirement between application and grain harvest, and the level or length of control achieved. All of them will require thorough spray coverage to be most effective. Another herbicide that is sometimes mentioned as a possible pre-harvest treatment is paraquat or Gramoxone. Paraquat is not labeled for pre-harvest treatment in wheat. Application of paraquat to wheat is an illegal treatment and can result in a quarantine and destruction of the harvested grain, along with severe fines.
Herbicides for use as pre-harvest weed control options in wheat:
Aim EC (1 to 2 oz.), acts quickly, usually within 3 days, controls only broadleaf weeds, has a 7-day pre-harvest interval. Dicamba (0.5 pt.), acts slowly to kill weeds, controls many broadleaf weeds, 7 day pre-harvest interval. Glyphosate, acts slowly it may take up to 2 weeks to completely kill weeds and grasses, 7 day pre-harvest interval. Metsulfuron (0.1 oz.), acts slowly, controls only susceptible broadleaf weeds, 10 day pre-harvest interval. Sharpen (1 to 2 oz.), acts slowly, controls broadleaf weeds, may take up to 10 days to completely kill weeds, 3 day pre-harvest interval, one month rotation interval for soybeans. 2,4-D LVE, acts slowly, 14 day pre-harvest interval.
It is very difficult to estimate the value of pre-harvest weed treatments as it will depend in part on the differences a treatment would have on harvest efficiency and dockage. It may not pay to treat wheat with lower weed densities unless harvest is delayed. If the weeds are about to set seed, a pre-harvest treatment can go a long way toward reducing weed problems in future years by preventing seed production. It is the end user’s responsibility to always read and follow herbicide label directions.
Cottonwood Extension District, Hays