You might think it is a bit early to start thinking about those weeds that can magically appear in your wheat fields. But now is the time to start planning and scouting! Weeds compete with wheat for light, water, nutrients, and space. Uncontrolled weeds in wheat decrease yields, lower quality and interfere with harvest.
It is important to scout fields and properly identify young weed seedlings early in the season to develop an effective weed management strategy. Understanding the life cycle of the weeds will also help with identification and control. Basically weeds are divided into different categories depending on their emergence and growth pattern.
There are winter annuals, summer annuals and perennials. Winter annual weeds generally emerge in the fall of the year, go dormant over winter, resume active growth in the spring, and then flower and set seed before dying in the summer. Winter annual weeds are generally most susceptible to herbicides in the fall or before they have begun to bolt or joint in the spring.
These include grasses and broadleaves such as cheat grasses, jointed goat grass, mustards, field pennycress or henbit. Winter annual weeds are usually the most abundant type of weeds in winter wheat because they have a similar life cycle.
There are several herbicide options for controlling winter annual broadleaf weeds in wheat. Generally, fall applications will provide the best control of winter annual weeds with any herbicide, as long as the weeds have emerged.
The majority of winter annual weeds usually will emerge in the fall, although you can still have some emergence in the spring, especially if precipitation after planting is limited in the fall. However, winter annual weeds that emerge in the spring often are not very competitive with the crop, at least in years when there is a good crop stand. This year, may be a different story with the limited growth of the wheat crop.
Some herbicides can work well even when applied during the dormant part of the season, while others perform best if the crop and weeds are actively growing. The key difference relates to the degree of soil activity provided by the herbicide.
Herbicides that have good residual activity, such as Glean, Finesse, Amber, and Rave can generally be applied in February when plants aren’t actively growing and still provide good weed control, assuming you have proper conditions for the application.
Most other herbicides, which depend more on foliar uptake, will not work nearly as well during the mid-winter months, when the wheat and weeds aren’t actively growing, as compared to a fall or early spring application. This may be especially true this year due to the colder temperatures and dieback of foliage this winter.
Spring herbicide applications can be effective for winter annual broadleaf weed control as well, but timing and weather conditions are critical to achieve good control. Spring applications generally are most effective on winter annual broadleaf weeds soon after green-up when weeds are still in the rosette stage of growth, and during periods of mild weather.
Once weeds begin to bolt and wheat starts to develop more canopy, herbicide performance often decreases dramatically.
The “2018 K-State Research and Extension Chemical Weed Control” publication is available online. The publication is also available, in print at NO COST, at any of our Post Rock Extension District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center. The publication is an excellent resource that provides the effectiveness of different herbicides for each of our major crops.