Pre-plant herbicide for kochia control

Stacy Campbell, K-State Extension

Now is the time to finalize plans for kochia (aka fireweed) 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 and have dense hairs that make adequate post herbicide coverage and adsorption difficult, with disappointing results. 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.

Herbicide program components

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

— a very soluble and effective herbicide that can be incorporated with very little precipitation, such as dicamba; and

— an 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.

If it is difficult for a grower to apply pre-emerge herbicides in early Spring. A Fall-applied treatment can also be effective to help ensure timely application, and good control, however, they are not likely to effectively control later flushes of kochia.

The duration of a fall applied herbicide in early December and combined with a spring pre-emerge application in late February has achieved greater than 80% control of kochia in Kansas. These treatments were conducted in Tribune and Garden City by K-State Weed Science specialist. They used three different treatments and each one was equally effective. They were ATZ + Clarity + Sharpen; ATZ + Clarity + Zidua; and Atrazine + Clarity.

Don’t forget several Extension Districts in the area are hosting a weekly “Crop Talk – virtual webinars” each Tuesday and some Wednesdays beginning at 10:30 a.m. You will need to register in order to get the link to the Zoom or YouTube connection. http://tinyurl.com/croptalk

1.    Corn Insect Resistance: Rootworm and Western Bean Cutworm, February 16

2.    Grain Sorghum Weed Control: Start clean…..Stay clean! February 23

3.    Sorghum Insects: Aphids, Headworms and Chinch bugs…..Oh my! February 24

4.    Alfalfa Management for Insects and Adverse weather, March 2

5.    Dryland Corn Dynamics, March 9

Stacy Campbell is an Agriculture and Natural Resources agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at scampbel@ksu.edu or calling 785-628-9430.