If you wait to inspect wheat for weeds until you see blue mustard already flowering, you likely have sacrificed yield. In fact, if it is a heavy infestation, yield losses could be severe.

“To minimize yield losses, mustards should be controlled by late winter or very early spring, before the stems begin to elongate or bolt,” says Sarah Lancaster, a weed management specialist with Kansas State University Extension. “If mustards are present in the fall, they can be controlled by various active ingredients.”

Lancaster co-authored Control of mustards in wheat: Timely treatment is important with Jeremie Kouame, weed scientist at the KSU Ag Research Center in Hays.

Farm Progress posed questions to Lancaster and Kouame about controlling mustards in wheat. Here are their responses:

How do mustards result in yield loss? Is it a problem in all wheat types?

Lancaster: Because mustards have a life cycle resembling winter wheat, they are strong competitors for water and nutrients, ultimately resulting in yield loss if not controlled. Our colleagues to the north worry more about annual grasses in spring wheat.

Kouame: Results from earlier research reported up to 50% wheat yield reduction from blue mustard competition.

What herbicide options are available?

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Lancaster and Kouame: Look for products containing Group 2 herbicides such as chlorsulfuron, active ingredient in Glean and other products; metsulfuron in Ally and others; triasulfuron, active ingredient in Amber plus others; propoxycarbazone, in Olympus and others; or pyroxsulam, in PowerFlex and others. Premixes of thifensulfuron plus tribenuron are marketed as Affinity and others. Most ALS-inhibiting herbicides control winter annual mustards very well. However, there are populations of bushy wallflower and flixweed in Kansas that are ALS-resistant and cannot be controlled by these products.

Note that some Group 2 herbicides have long rotation intervals for other crops.

If you are spraying wild mustard, are spray volumes and nozzle selection important?

Lancaster: Spray volume and nozzle selection are always important to optimize for postemergence herbicide applications, largely due to their influence on droplet size. Check labels of products to make sure your setup will achieve recommended droplet size.

Kouame: Spray volumes and nozzle selection affect droplet size and control. The label of each chemistry will guide about optimum spray volume and appropriate nozzle type and size. Selecting the right nozzle will help achieve the right droplet spectrum. In general, droplet size influences spray drift, deposition, spray coverage, canopy penetration and biological efficacy.

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How can growers control ALS-resistant mustards?

Lancaster: Group 27 herbicides like Huskie (pyrasulfotole) or Talinor (bicyclopyrone) can control ALS-resistant mustards. Other options are Group 4 herbicides like 2,4-D and MCPA. Dicamba and fluroxypyr, marketed as Starane or others, are not very effective for mustard control. Quelex, which is halauxifen plus florasulam, and Tarzec, halauxifen plus pyroxsulam, are also labeled for control of some mustard species.

Group 27 and Group 4 herbicides have little to no residual activity. Applying them with fertilizer in January or February when weeds are dormant will not provide good mustard control. Make sure wheat is fully tillered when 2,4-D is applied to avoid reduced tillering.

If Group 27 and Group 4 herbicides aren’t effective in January or February, is the better option waiting until spring?

Lancaster: Herbicides will only control weeds that are actively growing. Early scouting for a fall application would be best, assuming wheat is an acceptable size for products applied. An early spring application would also be effective.

How can growers time applications for troublesome species? 

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Lancaster: In late winter or early spring, blue mustard is the most difficult winter annual broadleaf weed to control. It bolts very early. Herbicides typically need to be applied on blue mustard in late February or early March. Thus, 2,4-D is often applied too late to be effective on blue mustard because it has already bolted by the time it is safe to apply 2,4-D on wheat.

Flixweed and tansy mustard should be treated when no larger than 2 to 3 inches across and 2 to 3 inches tall. Control decreases dramatically with larger plants. Ester formulations of 2,4-D and MCPA are more effective on tansy mustard and flixweed than amines. Field pennycress is easier to control than tansy mustard or flixweed. Herbicide applications made before pennycress bolts are usually effective.

You note that blue mustard can be hard to control with 2,4-D. Is there something else that can control blue mustard at that time?

Lancaster: Once weeds bolt, the amount of leaf area available to absorb herbicide decreases relative to total plant size. Most herbicides will be less effective then. Common herbicides that we might consider are Glean or Finesse, assuming the blue mustard population is ALS-susceptible.

Kouame: For weed control, it is always good to be timely. Some control might be achieved then. Realize that mustards that have emerged early are most competitive for limited resources. Delaying applications might make the economics of later control less favorable. However, a later control may still reduce seed production and dispersal.

What else can work besides herbicides?

Lancaster: Crop rotation with corn, grain sorghum, soybeans, cotton or sunflowers is a good way of managing mustards if they are controlled before producing seeds. Crop rotation will usually result in a gradual reduction of mustard populations as the seed bank decreases.

Prevention is also a helpful strategy for the long-term management of mustards. Managing mustards in roadsides and field borders can prevent movement into cultivated fields. Also, cleaning equipment when moving from infested to noninfested fields reduces mustard dispersal.

Why does crop rotation work?

Lancaster: Rotating to summer crops allows mustards to be controlled in the spring, before planting. There are more herbicide options in a noncrop situation. Tillage becomes an option for control before planting.

Kouame: Crop rotation is a key component of best management practices for preventing herbicide resistance evolution and for controlling herbicide-resistant weeds. The risks of resistance evolution are lower in systems where crop rotations are practiced. Also, rotating different herbicide-resistance crop traits in different crops increases herbicide mode-of-action diversity within cropping systems.