Weed control in winter wheat is aided by the crop’s fall-growth habit, vigorous spring growth, and early maturity. This benefit not only is of value in the year winter wheat is grown, but is also an important tool for maximizing the effectiveness of other crop protection products in other crop years. For example, avoiding a graminicide during the winter wheat year can help avoid or manage the development of herbicide resistance.
By incorporating winter wheat and these weed management practices into your rotation, you can be certain that not only your winter wheat, but also all subsequent crops in your rotation will reap the rewards of having lower weed pressure.
In situations where winter wheat is less competitive, such as late seeding in fall or winter injury, more intensive wheat management may be needed to achieve maximum yields.
Winter wheat is no different than other crops in its need to have a competition-free establishment period. Controlling weeds prior to seeding is a particularly effective time for that second step in control of biennial, perennial, and winter annual weeds, especially downy brome. Glyphosate products provide the most effective control in this window for weed control.
Pre-seeding herbicide applications also control early emerging volunteer plants. Control of volunteer seedling is particularly important when seeding into wheat stubble. Pre-seed glyphosate one to two weeks prior to seeding will break the “green bridge,” preventing wheat streak mosaic virus from carrying over to the winter wheat crop. Some growers tank mix residual broadleaf chemistry with their glyphosate to extend the weed control into winter wheat emergence and establishment. Early emerging weeds are generally some of the most competitive weeds a crop has to face. Removing early weed competition helps develop a well-established winter wheat crop, which will have a better ability to survive the winter.
Controlling winter annual weeds is the next important step in successful winter wheat production. Common winter annual weeds include stinkweed, shepherd’s purse, and flixweed. Due to their habit of emerging in the fall and resuming growth early in the spring, winter annuals can be very competitive and difficult to control in the spring. This makes fall control a very practical and cost effective approach to controlling winter annuals if sufficient densities are present. Herbicide applications should target actively growing plants that are able to metabolize the product quickly. According to Brian Beres of Agriculture and Agri-Food Canada, “Fall 2,4-D when used in the form and rate specified above is very effective in the control of winter annuals and I prefer it to any spring phenoxy applications as it’s very hard to apply in spring before the plant stage is too advanced.”
Considerations for spring in-crop weed control in winter wheat are generally very similar to any other cereal crop. In-crop applications in spring generally occur at times that coincide with pre-seeding glyphosate applications and seeding operations. Waiting until spring seeding is complete to spray winter wheat often results in poor weed control due to weeds becoming too large. The early growth habit of winter wheat also leads to increased crop canopy cover and potential crop injury due to the herbicide being applied beyond the safe application stage.
Grassy winter annual weeds such as Japanese brome and downy brome can be particularly difficult problems for winter wheat. Japanese brome can be controlled with a fall or spring application of pyroxsulam herbicide. Initial studies indicate that flucarbazone and new chemistries flumioxazin and pyroxasulfone also have good promise for Japanese brome control, but these are not registered for use on winter wheat at this time.
Downy brome is a more difficult winter annual weed to control. Pyroxsulam is registered for control of downy brome in fall applications and suppression for spring applications. As with Japanese brome, new chemistries flumioxazin and pyroxasulfone also show good promise for downy brome control, but are not registered for use on winter wheat at this time.