Herbicide options for burndown of existing weeds prior to planting of no-till wheat include glyphosate, Gramoxone, Sharpen and dicamba. Dicamba labels have the following restriction on preplant applications – “Allow 10 days between application and planting for each 0.25 lb ai/A used”. A rate of 0.5 lb ai/A would therefore need to be applied at least 20 days before planting. We do not know of any 2,4-D product labels that allow preplant application in wheat, and Liberty is not approved for this use either.
The primary targets for a preplant burndown in wheat are the small, emerged winter annual weeds that can overwinter and have a negative effect on wheat the following spring. This includes marestail (horseweed), chickweed, deadnettle, annual bluegrass, mustards, etc. Herbicide treatments at this time can also have considerable activity on biennials (wild carrot, wild hemlock), dandelion, and Canada thistle, although herbicides are often more effective on these weeds later in the fall. While glyphosate can adequately control small winter annual weeds, it should be combined with Sharpen or dicamba in fields with a history of marestail problems (or in fields downwind of a neighbor’s marestail nightmare). Gramoxone should also effectively control small seedlings of marestail and other winter annuals. Be sure to use the appropriate adjuvants with Sharpen or Gramoxone, and increase spray volume to 15 to 20 gpa to ensure adequate coverage.
There are several effective postemergence herbicide treatments for wheat that can be applied in November to control winter annual weeds, in fields where preplant burndown treatments are not used. Effective postemergence treatments include Huskie or mixtures of dicamba with Peak, tribenuron (Express etc), or a tribenuron/thifensulfuron premix (Harmony Extra etc), among others. Huskie may be the most effective fall postemergence treatment for control of marestail, where the marestail population is resistant to ALS inhibitors. We discourage application of 2,4-D to emerged wheat in the fall due to the risk of injury and yield reduction.