Spring Wheat Herbicide Use

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• Wheat fields have resumed growth, time to think about weed control.
• Wild garlic should be controlled, even if densities are low to avoid market dockage.
• Be aware of plant back restrictions following some herbicides if soybeans will be planted after the wheat crop.

Warmer temperatures over the past few weeks have allowed winter wheat fields to green up and resume growth. During winter wheat green-up, there are a few field activities that need to be considered, including winter wheat herbicide applications. The following information will outline winter annual weeds to look out for, weed scouting tips, crop stage restrictions, and herbicide recommendations.

Some common broadleaf weeds to scout for in winter wheat are dandelion, purple deadnettle, henbit, chickweed, Canada thistle, wild garlic, marestail, and annual ryegrass if you are in the southern part of Midwest. These weeds emerge in the fall and can remain relatively inconspicuous through the winter; however, they become competitive and troublesome during the spring if not controlled early. Summer annual weeds such as ragweed will be of less concern in the early spring and will be outcompeted by the wheat crop if managed properly. Grass weeds that commonly require spring herbicide applications in wheat include annual bluegrass, annual ryegrass, cheat, and downy brome.

The majority of wheat herbicides are labeled for application at certain wheat growth stages, and some commonly used herbicides have very short windows in which they can be applied. For example, 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restrictions for other herbicides are outlined in Table 1.

Application of herbicides in liquid nitrogen fertilizer solution as a carrier is commonly done to reduce trips across the field. Caution should be taken when using liquid fertilizer as a herbicide carrier as moderate to severe crop injury can result, especially in cool, cloudy weather conditions. Many POST-applied wheat herbicide labels allow for liquid nitrogen carriers but require different rates and types of surfactants than if the herbicide was applied with water as the carrier.  Table 1 includes precautions to be taken when applying wheat herbicides using liquid fertilizer as a carrier; further details and directions can be acquired from the herbicide label.

Another consideration when planning early spring herbicide applications is the plant-back restriction to double-crop soybeans. A large percentage of the herbicides listed in Table 1, especially those with activity on annual ryegrass and downy brome, have soybean plant back restrictions greater than the typical three-month time period between spring applications and double-crop soybean planting. The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double-crop soybeans after wheat. Refer to Table 1 for more specific soybean back timing restrictions.

Table 1.  Spring applied wheat herbicide rates, crop stage restrictions, weed control spectrum, soybean plant back timing, and liquid fertilizer carrier recommendations.

* The highest labeled herbicide rates should be used to achieve control of dandelion plants with spring applications.