Weed control must be based on clean field selection and shallow seeding for quick and uniform emergence to obtain a good, uniform stand. The mustard crop should not be harrowed, rotary hoed or tilled after emergence.
Weeds are a serious problem in mustard production. They not only reduce yields, but weed seeds such as wild mustard, wild buckwheat and foxtail, as well as canola, are difficult to remove and can cause severe cleaning losses and market grade reductions. Such losses reduce profits to the grower.
Mustard plants are sensitive to herbicides such as 2,4-D, Banvel, MCPA, glyphosate, and most ALS herbicides, including imidazolinone and sulfonylurea-type herbicides. Spray drift and sprayer tank contamination must be avoided.
All mustards, but especially the oriental and brown types, should be sown on fields known to be relatively free of wild mustard infestation. Wild mustard can be separated mechanically from yellow mustard with large seed, but separation is not possible with the brown and oriental mustards. Wild mustard contamination will reduce grades of mustard, resulting in severe market discounts.
Treflan, or generic trifluralin, is labeled for grass control and some broadleaf weed control in mustard. Trifluralin will not control wild mustard. Trifluralin must be applied prior to seeding and incorporated thoroughly in the soil for maximum effectiveness. Spring or fall application and incorporation are labeled. Rates should be adjusted according to soil type.
Quizalofop or clethodim can be post-applied prior to bolting for control of certain annual grasses and quackgrass. Applications are 7 to 12 fluid ounces (fl. oz.) EC for Assure II or Targa and 0.77 to 1.32 oz. per acre for quizalofop. Applications are 9 to 12 fl. oz. per acre of Select Max 1EC, 4 to 6 fl. oz. per acre of Select 2EC, 2.66 to 5.33 fl. oz. per acre of Shadow 3EC or 1 to 2 oz. per acre of clethodim.
Grass weeds should be 5 inches or less in height. Allow a 60-day (quizalofop) to 70-day (clethodim) post-interval after spraying before harvesting the crop. The grass herbicides should be applied using an oil adjuvant at 1% on a volume for volume basis, but not less than 1.25 pints per acre.
For more details, see the current year of the NDSU Extension publication “North Dakota Weed Control Guide” (W253), and always follow the directions on the label.