Managing key grass weeds in spring wheat and barley

Introduction

It is important for producers to understand the herbicide options and strategies available for grass weed control when considering a spring wheat or spring barley crop. When considering planting either spring wheat or spring barley it is important to identify the potential weed species that could cause potential yield loss. Despite the ability of the crop to compete with annual grass weeds, especially standard height spring wheat varieties, there are many weed species that can persist and cause potential yield loss in spring planted small grains. Some of the annual grass weed species that are often a problem in spring wheat or barley production include:

1. Wild oats.
2. Green or yellow foxtail.
3. Barnyardgrass.
4. Persian darnel.

Herbicide options

In-crop annual grass control

This herbicide option is currently the most popular. Using a post-emergence herbicide application is often required to be applied early after crop emergence. Depending on the herbicide used the application should take place at the one to 6 leaf and 3 tillers growth stage. Delayed application may allow more weeds to emerge, but the risk is then that the larger growth stage of any early emerging weeds will make management more difficult. A thick, heavy stand of wheat or barley will effectively compete with weeds during early growth stages.

One important consideration is some broadleaf herbicides could cause antagonism when tank mixed with a grass herbicide. This antagonism can reduce the herbicide efficacy. If the preferred broadleaf herbicide is known to have a grass herbicide antagonism, then in most cases, it is best to make the grass herbicide application first followed by a separate broadleaf herbicide application. There are many more herbicide options for broadleaf weed control in spring wheat and barley than for annual grass weed control, so it is important to develop a herbicide program early during the planning process that most effectively manage the weed species present in each field. Additionally, the broadleaf herbicide will have certain growth stages that it can be applied to the wheat or barley and it is important to apply both herbicides at their proper timing.

With any herbicide application it is important to understand multiple production considerations including:

1. Weed species controlled.
2. Crop safety.
3. The labeled application window.
4. Approved tank mix partners.
5. Re-cropping restrictions.
6. Ground and or aerial application.

Multiple modes of action or active ingredient herbicides

Tank mix partners that contain multiple modes of action or multiple active ingredients offer the potential for increased weed control of hard to control weed species. Utilizing multiple modes of action can also help reduce the potential for the development of chemical resistance in the weed population.

Cirray™ Herbicide from Bayer^® is a powerful tool in the fight against stubborn wild oats. Its unique Group 1 combination provides premium control of wild oats, barnyardgrass, green and yellow foxtail and Persian darnel in spring wheat and barley while supporting multiple broadleaf tank mix partners with a wide window of application. Bayer^® is the first to introduce fenoxaprop, a Group 1 herbicide, alongside pinoxaden, another Group 1 herbicide, but with a different active ingredient, for spring planted wheat and barley for Canada.¹

Cultural Control

Cultural controls of weeds should not be considered as a stand-alone weed control plan but as a means of control used to help prevent a weed problem or to decrease the level of weed pressure before the crop is planted. Cultural control options can include these types of production practices:

1. Use low disturbance drill to plant the crop at a shallow depth to reduce soil disturbance that can help reduce weed seed germination.
2. Planting fields that have a known high wild oat weed pressure last as a delayed planting can reduce weed pressure over time.
3. Delay planting fields that have a known high wild oat pressure, this will allow a more effective timing of the in-crop herbicide application.
4. Use a crop rotation that has a diversity of plant types and herbicide options that utilizes other modes of action in your chemical control plan.
5. Use a heavier seeding rate of up to 25% higher rate to have a vigorous, healthy crop stand to better compete with the weeds.²
6. Sanitation – always plant a good clean source of seed.

Annual seedling grass identification

Successful annual grass control measures depend on accurate identification of seedling grass species. Annual grass weeds can be difficult to identify in the seedling and early vegetative growth stages. To identify many of these subtle distinguishing plant characteristics a pocket lens or a 10X magnification scope can be helpful to accurately distinguish between the distinctive characteristics. A successful herbicide application is often dependent on an early application which is often recommended in the one to three leaf growth stage, so an early and accurate identification is extremely important. Identification of several key grass plant parts are critical to aid in identification of weed species that might be a problem in a spring wheat or spring barley field.

Wild oat (Avena fatua L.)

Wild Oat Seedlings have a membranous ligule, no auricles, leaf blades and sheath are hairless or sparsely hairy and the leaf blade is narrow and upright and has a counterclockwise twist often with a bluish tint.

Barnyardgrass (Echinochloa crus-galli)

Seedlings lack hairs (glabrous), auricles, and ligules, and the leaf sheaths are distinctly flat by the third leaf growth stage, often tinted red or maroon at the base.

Green foxtail (Seteria viridis)

Seedlings have a hairy ligule, the leaf blade has little or no hair, and the sheath margin is hairy.

Yellow foxtail (Setaria pumila)

Seedlings of yellow foxtail have a hairy ligule. The leaf blade has long hair on upper surface only near the base by third leaf stage. The sheath is flat without hair, often with a reddish base.

Many weed ID guides are available from your local provincial agricultural publication source. One such guide, Weed Seedling Guide 2^nd Edition, is available at https://www.agric.gov.ab.ca/app08/ppslogin?pID=298.

If there are questions about identification of a specific weed, local agronomists are a great resource as well.

Conclusion

When considering any herbicide application always follow the pesticide label and directions. Local Ag Chemical suppliers can help select products and timing that have been working in the area. They can also help ensure application timing is scheduled for maximum control and minimum concerns for crop injury. It is important to develop a weed control plan prior to the season, if needed, to make a herbicide decision soon after the crop emerges so as to not let the weed get too large and allow the application to follow the label for maximum weed control.