Pre-Plant Herbicide Applications For Kochia Control

Now is the time to finalize plans for kochia control. Recent research suggests that kochia can begin emerging in early February with most kochia emerging by early April. Kochia seedlings emerge in dense populations that make adequate herbicide coverage difficult (Figure 1). In addition, glyphosate-resistant kochia is prevalent across western Kansas, making kochia control even more challenging. For these reasons, it is important to apply pre-emergence herbicides in late winter or early spring to control this weed before it emerges. This article will be the first in a series discussing specific options for various cropping scenarios.

Figure 1. Emerged kochia seedlings in a fallow field. Photo by Sarah Lancaster, K-State Research and Extension.

Herbicide program components to effectively manage kochia at germination

To successfully manage kochia, a herbicide program needs two components:

1. a very soluble and effective herbicide that can be incorporated with very little precipitation, such as dicamba; and
2. a herbicide that has longer residual activity, which will require perhaps 0.75 inches or more precipitation for adequate incorporation, such as atrazine.

Precipitation events during late winter are often too small to activate longer residual herbicides, but dicamba may control kochia for 4 to 6 weeks until the longer residual herbicide is incorporated.

The best timing to apply herbicides for kochia control is generally January through the first week of March but prior to kochia emergence, which can vary depending on weather conditions. Later applications, for example, at the time of burndown, are more likely to occur after kochia emergence, which increases the risk of control failure (Figure 2). Fall-applied treatments can help ensure timely application, however, they are not likely to effectively control later flushes of kochia (Figure 3).

Figure 2. EPP/POST herbicides applied March 10, 2015 for kochia control at Tribune, KS. Kochia at cotyledon stage. Graph by C. Thompson, K-State Research and Extension.

Figure 3. Duration of anticipated kochia control greater than 80% following fall (December 4) and spring (February 23) herbicide applications at two locations during 2015. Data from Vipan Kumar, K-State Research and Extension.