With more and more no-tillage acres planted with winter wheat, farmers across the region are seeing an increase in the abundance of winter annual weeds such as cheatgrass, jointed goatgrass, field pennycress, wild mustard, shepherd's purse, catchweed bedstraw, common chickweed and prickly lettuce. Understanding how winter annual plants grow can help farmers enhance the success of their weed management plans.

Annuals plants complete their life cycle in less than one calendar year. Although some winter annuals can overwinter as seeds and germinate in the early spring, they typically germinate from late summer to early winter, overwinter as small plants, and grow rapidly as temperatures warm in the spring. Winter annuals flower, set seed and mature by early summer. These seeds lie dormant in the soil during the rest of the summer months. Because of their lifecycle, winter annual weeds are well adapted to grow in cool, humid conditions, use the moisture available in early spring, and survive during the limited summer rainfall conditions.

The potential for winter annuals weeds to reduce winter wheat yield and interfere with production depends upon the severity of infestation. Fields with a short history of no-tillage or that have been planted into spring crops often have small, scattered patches of winter annual weeds. Although these weeds may not interfere with crop growth, if left uncontrolled patches can expand through time.

As a rule, the best time to manage winter annual weeds is in the fall. However, winter wheat growers have several options to manage winter annuals in spring.

As growers look for weed control options, they must keep in mind that herbicide safety and performance will depend on the stage of the wheat and the weed spectrum present in the field. For example, although fall applications of 2,4-D have good standards for crop safety, caution should be used when spraying this herbicide in the spring. 2,4-D can be applied between the four-tiller to joint stage, but crop injury could occur if a spring frost follows herbicide applications and/or the crop is already too advance and unable to metabolize the herbicide's active ingredient. Tank mixing dicamba (Banvel or Clarity) with 2,4-D can further enhance the risk of herbicide damage. Other growth regulator herbicides that can be applied to winter wheat prior to jointing include MCPA, and Curtail (2,4-D amine-plus-Stinger). Huskie, Affinity Broadspec, Aim, Bronate Advance, and Ally Extra can also be used to manage weeds in winter wheat in early spring.

Farmers should remember that the adoption of no-tillage systems has increased our reliance on herbicides. While this approach to farming has benefits in terms of reducing soil erosion and energy use, it increases the potential for selection of herbicide-resistant weeds. The use of herbicides with different sites of action, applied as tank mixes, premix formulations, or sequential applications, can help in managing resistance.

Disclosure. Common chemical and trade names are used in this publication for clarity by the reader. Inclusion of a common chemical or trade name does not imply endorsement of that particular product or brand of herbicide and exclusion does not imply non-approval.

Contact: Fabian Menalled (406) 994-4783 or menalled@montana.edu