Kochia Control

Kochia - The Basics

Kochia (Kochia scoparia (L.) Roth) continues to be a serious weed problem in western Kansas, especially with the development of resistance to atrazine, ALS-inhibitor, and glyphosate herbicides. Controlling this weed can be challenging, but it helps to understand the biology of kochia. In particular, it helps to know when kochia emerges from the soil and for how long it can emerge during the season.

How Widespread is the Problem? Herbicide Resistance in Kochia

Kochia has long been a serious weed problem in western Kansas, but getting good control of kochia has become even more of a challenge in recent years as populations resistant to atrazine and ALS-inhibitor herbicides have developed. Now there are confirmed populations of glyphosate-resistant kochia sampled during 2007 from several counties in western Kansas. Many more such populations are suspected.

Controlling Annual Weeds with Fall-Applied Herbicides Ahead of Corn and Sorghum

With row crop harvest underway, it's time to start planning your fall herbicide applications to control winter annual broadleaf weeds and grasses ahead of grain sorghum or corn. Fall applications during late October and through November can greatly assist control of difficult winter annuals and should be considered when performance of spring-applied preplant weed control has not been adequate. Henbit and marestail frequently are some of the most troublesome weeds we try to manage with these fall herbicide applications.


Fall applications have another side-benefit. While it is always important to manage herbicide drift, herbicide applications made after fall frost have less potential for drift problems onto sensitive targets.


There are several herbicide options for fall application. If residual weed control is desired, atrazine is among the lowest-priced herbicides. However, if atrazine is used, that will lock the grower into planting corn or sorghum the following spring, or leave the land fallow during the summer and come back to winter wheat in the fall.


Atrazine is labeled in Kansas for fall application over wheat stubble or after fall row crop harvest anytime before December 31, as long as the ground isn't frozen. Consult the atrazine label to comply with maximum rate limits and precautionary statements when applying near wells or surface water. No more than 2.5 lbs of atrazine can be applied per acre in a calendar year on cropland.


One half to two pounds (maximum) per acre of atrazine in the fall, tankmixed with 1 to 2 pints/acre of 2,4-D LV4 or 0.67 to 1.33 pints LV6, can give good burndown of winter annual broadleaf weeds -- such as henbit, dandelion, prickly lettuce, Virginia pepperweed, field pansy, evening primrose, and marestail -- and small, non-tillered winter annual grasses. Atrazine's foliar activity is enhanced with crop oil concentrate, which should be included in the tankmix. Winter annual grass control with atrazine is discussed below.


Atrazine residual should control germinating winter annual broadleaves and grasses. When higher rates of atrazine are used, there should be enough residual effect from the fall application to control early spring-germinating summer annual broadleaf weeds such as kochia, common lambsquarters, wild buckwheat, and Pennsylvania smartweed – unless the weed population is triazine-resistant. The two graphs below show the residual control effects of December herbicide applications on kochia ahead of corn and sorghum planting.

kochia control graph 1

kochia control graph 2

Figure 1 and 2. K-State trials measuring kochia control with late-fall herbicide applications. Source: Curtis Thompson, K-State Research and Extension.

Marestail is an increasing problem in Kansas that merits special attention. Where corn or grain sorghum will be planted next spring, fall-applied atrazine plus 2,4-D or dicamba have effectively controlled marestail rosettes, and should have enough residual activity to kill marestail as it germinates in the spring. Atrazine alone will not be nearly as effective postemergence on marestail as the combination of atrazine plus 2,4-D. Sharpen can be very good on marestail, but should be tankmixed with 2,4-D, dicamba, atrazine, or glyphosate to prevent regrowth.


If the spring crop will be corn, other residual herbicide options include ALS herbicides such as Autumn Super or Basis Blend. ALS-resistant marestail will survive an Autumn Super or Basis Blend treatment if applied alone. For burndown, producers should mix in 2,4-D, dicamba, and/or glyphosate. Aim + 2,4-D or Rage D-Tech are additional herbicide options for fall application with only the 2,4-D component providing a very short residual.


Winter annual grasses can also be difficult to control with atrazine alone. Success depends on the stage of brome growth. For downy brome control, 2 lbs/acre of atrazine plus crop oil concentrate (COC) has given excellent control, whereas 1 lb/acre has given only fair control. Volunteer wheat and brome species that have tillered and have a secondary root system developing will likely not be controlled even with a 2-lb rate. Adding glyphosate to atrazine will ensure control of volunteer wheat, annual bromegrasses, and other winter annual grassy weeds. Atrazine antagonizes glyphosate, so if the two are used together, a full rate of glyphosate (0.75 lb ae) is recommended for good control. The tankmix should include AMS as an adjuvant.


Where fall treatments control volunteer wheat, winter annuals, and early-emerging summer annuals, producers should then apply a preemerge grass-and-broadleaf herbicide with glyphosate or paraquat at corn or sorghum planting time to control newly emerged weeds. Soils will be warmer and easier to plant where winter weeds were controlled in fall.

Curtis Thompson, Extension Agronomy State Leader and Weed Management Specialist
cthompso@ksu.edu

Kochia Control in Corn and Grain Sorghum

For fields that will be planted to corn this spring, a combination of glyphosate (using a minimum of 0.75 lb ae/acre) with herbicides that have PRE and POST activity on kochia are most valuable. Tank mixing 8 to 16 oz of dicamba and or 1 to 2 pints of atrazine, will control small kochia and other existing broadleaf and grass weeds. If producers wait until later so they can apply the burndown and preemergence herbicide in the same application, the kochia will be larger and most likely will not be controlled adequately. If that occurs, the surviving plants will go on to cause problems throughout the growing season.

Kochia Control in Sunflower and Soybeans

The development of populations of kochia resistant to either ALS-inhibitor herbicides, glyphosate, and/or triazines in Kansas means that producers may have to put a little extra time and effort into controlling this tough summer annual broadleaf weed. Control can still be achieved in almost all cases in both sunflower and soybeans, especially if: (1) a combination of herbicides is used with different modes of action, and (2) control measures begin early in the spring.

Kochia Control in Wheat