Producers should start this winter in planning their program for controlling kochia in corn and grain sorghum. Recent developments with glyphosate-resistant kochia populations and the difficultly growers have had controlling these populations suggest that perhaps control measure should begin prior to emergence of kochia.

Huge flushes of kochia emerge in late March and into April. Applying 8 to 16 oz/acre of Clarity/Banvel or using a pound of atrazine around mid-March, before the kochia has emerged, could provide significant control of early flushes of kochia. The addition of 2,4-D will help control winter annual mustards. This will make subsequent kochia control measures discussed in this article more effective. When treating kochia with postemergence burndown or in-crop herbicides, spray early when the plants are about 1 to 3 inches tall. 

Control in corn

Kochia control in corn should always include either tillage or a burndown application in April, shortly after the first kochia has emerged. A combination of glyphosate and dicamba will control small kochia, and almost all other existing weeds and grasses, at that time. If producers wait until later so they can apply the burndown and preemergence herbicide in the same application, the kochia will be larger and they may not get complete kochia control. If that occurs, the surviving plants will go on to cause problems throughout the growing season.

The label for Clarity states that no more than 32 oz/acre can be applied per season. If 8-16 oz/acre is applied in March as an early preplant and 8 oz/acre is applied as a burndown ahead of corn or sorghum planting that still allows for an 8 oz application in-crop, which is often more than what is used in-crop.

After the early April burndown treatment, the next step would be a preemergence herbicide application. Atrazine, or a product containing atrazine, should be included with this application. Even if there are triazine-resistant populations of kochia present, atrazine will still help control a number of other weed species.

Good options to include in a preemergence application for control of kochia (and other weeds) include:

* A chloroacetamide/atrazine premix. Examples of chloroacetamide-atrazine premixes include Bicep II Magnum, Cinch ATZ, Guardsman Max, Propel ATZ, Bullet, Harness Xtra, Keystone, Volley ATZ, FulTime, and others. If triazine-resistant kochia is present, then one of the other options would be the better choice.

* An HPPD herbicide. Examples of HPPD herbicides include Lexar or Lumax (premixes of Callisto, Dual II Magnum, and atrazine), Corvus (a premix of Balance Flexx and thiencarbazone methyl), and Balance Flexx.

* Verdict, formerly known as Integrity, which is a Kixor-powered combination of Sharpen and Outlook herbicides.

* Prequel, which is a premix of Resolve and Balance.

Balance Flexx, Corvus, and Prequel cannot be applied on coarse-textured soils with shallow (25 feet or less) groundwater. Always consult the labels for details.

If kochia becomes a problem after the corn has emerged, there are several postemergence herbicide options. In Roundup Ready corn, glyphosate should be used even though resistant populations of kochia may be present. It is also a good idea to add one or more herbicides with a different mode of action to the glyphosate. This will not only help control any glyphosate-resistant populations present, but will also help prevent the development of glyphosate-resistant populations of kochia where such populations do not yet exist.

Possible glyphosate tankmix partners would include Status, Impact, Callisto, Laudis, Starane, Starane NXT, or Starane Ultra. If an HPPD-containing herbicide was used in the preemergence application (Lexar, Lumax, Corvus, or Balance Flexx), it would be a good idea not to use this mode of action in the postemergence treatment to help reduce the chances of resistant weeds developing. Another option in Roundup Ready corn is Halex GT plus atrazine. Halex GT is a premix consisting of a high rate of glyphosate, Dual II Magnum, and Callisto. Atrazine should be added to this product to get the best season-long control of kochia. With Impact, Callisto, Capreno, and Laudis, producers should include a half-pound of atrazine. (Note: The herbicide Impact has been marketed by AMVAC through an exclusive licensing agreement with BASF, which owns the active ingredient, topramezone. That licensing agreement is no longer exclusive with AMVAC. Starting in 2012, BASF will also begin marketing topramezone under the tradename Armezon. Both Impact and Armezon will be 2.8 lb/gal topramezone.)

In conventional corn, any of those postemergence herbicides mentioned above as tankmix partners with glyphosate can also be used alone, without the glyphosate tankmix partner. Halex GT cannot be used on conventional corn since it contains glyphosate.

Ignite can also be used as a postemergence treatment if the corn is Liberty Link. Ignite alone will not control kochia, however. For kochia control, Ignite  should be tankmixed with Status or other more effective postemergence products. Ignite herbicides are soon to be renamed Liberty to better associate their use with Liberty Link crops. Existing stocks of Ignite products in the marketplace can still be used according to label directions.

It should be noted that Balance Flexx and Corvus can be applied either preemergence or up through the 2-leaf stage of corn. If applied postemergence to corn, Balance Flexx and Corvus can be applied with atrazine only. No glyphosate or other adjuvants can be used. These products can do an excellent job of controlling kochia throughout the season if they are tankmixed with at least 1 lb/acre of atrazine. These products require moisture for soil activation, however they do have foliar activity.

Lumax and Lexar, which are best used as preemergence treatments, can also be applied early postemergence up to 12-inch corn when weeds are very small. Although waiting until this stage before application may work for controlling kochia, it is risky. Also, to get adequate grass control, these products must be applied preemergence to the grass.