Grass Control in Fall Seeded Wheat

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Image source: https://www.syngenta.co.uk/pre-harvest-picture-grass-weed-problems

• Grass control from fall applications of herbicides is typically more successful than spring applications.
• Be aware of cold temperatures if using herbicides with foliar activity. Weeds must be actively growing for herbicides to be effective.
• There are many details to consider when choosing a herbicide for fall grass control in wheat.  Application timing relative to wheat and weed growth stage and plans for a rotational or “double” crop are two key considerations.

Winter annual grass weeds emerge mostly in the fall, although some can emerge in the spring as well. Wheat is a winter annual grass plant, and like winter annual weeds, it will emerge in the fall, go dormant in the winter and then resume growth in the spring. Winter annual grass weed establishment in the fall can lead to reduced wheat stands, which can impact wheat establishment and growth in the fall, and the number of harvestable plants the following year.

It is usually easier to control grass weeds in the fall with herbicide applications for the following reasons. Herbicides will have wider application windows based on weather and crop growth stage, and weeds are more likely to be actively growing in the fall than in the early spring due to warmer temperatures.

Although it can vary a little bit by geography, in general, the most common winter annual grasses infesting wheat are annual bluegrass, annual ryegrass, cheat, and downy brome. Table 1 provides a list of herbicides labelled for these species that can be applied in the fall, and their relative efficacy on each species as shown on page 4-2 of the 2024 FS Crop Protection Handbook.

Table 1. Relative effectiveness of fall applied herbicides for winter annual grass control. Data reproduced from the 2024 FS Crop Protection Handbook.

There are several key considerations with the herbicides that can be used for grass control in wheat. It is important to understand these so you can choose the product that best fits your situation. Here is a summary of things to consider when choosing a herbicide for grass control in wheat.

First, narrow down the list of herbicides that control the grasses in a specific wheat field based on an efficacy table such as the one listed in this article or one found in a University Extension weed control guide.

Second, determine if the herbicide is labeled in the state it will be used in. Some of these herbicides are not registered in all states. For example, Anthem Flex Axial Bold, and Axiom DF are not registered in New York. There are other herbicides that are not labeled in specific states as well. Consult the herbicide label to ensure it is labeled in the state it is being used in.

Third, some of these herbicides will have a relatively long rotational interval for planting subsequent rotational crops, like soybean. Consult the crop rotational intervals listed on the label or in the Crop Protection Handbook to review this information if you plan to plant a sensitive crop (or double crop) after wheat harvest in 2026.

Fourth, some of these herbicides have a wide application window and can be used from before emergence until the boot stage in the spring. Some of these herbicides will have application windows that starts at a specific wheat growth stage, such as the 2 leaf stage or tillering stage. In addition, some of these herbicides will have foliar activity on emerged weeds, some will just have residual in the soil on germinating weed seedlings (Axiom, Zidua). So, it is important to consider the application timing restriction with regard to wheat and grass weed growth stage to obtain maximum efficacy out of a specific product. 

For additional information about these herbicides, see the herbicide label and your FS Crop Specialist to help with the decision process.