They are out there. Their low-lying rosettes hiding amongst the wheat plants in your fields. Many growers do not recognize they have a mustard problem until the plants begin to bolt and send up their flowering stems, but by then, they have become difficult to control and they have accomplished much of their yield-robbing work.
Mustards need to be controlled by late winter or early spring, while they are still in the rosette stage of growth. Fields need to be scouted now, and treated as soon as possible if mustards are located.
Mustard control is much more difficult after plants shift from vegetative to reproductive growth, which is characterized by rapid stem elongation or bolting. There are a number of herbicides that can provide effective control of mustard species if they are applied early, before the mustard plants get big or begin to bolt. These include the ALS-inhibiting herbicides such as metsulfuron (Ally XP and other trade names), thifensulfuron + tribenuron (Affinity BroadSpec and other trade names), and pyroxsulam (PowerFlex HL and other trade names), as well as 2,4-D, MCPA, pyrasulfotole + bromoxynil (Huskie and other trade names), and bicyclopyrone + bromoxynil (Talinor). A tank mix of 2,4-D and one of the ALS-inhibiting herbicides is a relatively low cost and effective treatment, but it must be applied to mustard plants in the rosette stage of growth. Waiting to treat mustard plants until they begin to bolt dramatically reduces the effectiveness of herbicides and increases wheat yield loss.
The longevity of mustard seed in the soil, which is measured in decades, makes the prevention of seed production a critical component of managing these weeds. Consequently, later control treatments may still reduce seed production, which is beneficial in the long run.
To learn more about some of the most problematic mustard species in Eastern Washington and how to manage them, see the PNW Extension publication “Integrated Management of Mustard Species in Wheat Production Systems” (PNW703). Tally-ho!
For questions or comments, contact Drew Lyon via email at drew.lyon@wsu.edu or phone at 509-335-2961.