Kochia was in the process of emerging on March 10 in a field near Tribune. With windblown kochia plants rolling across the countryside, seeds have been widely distributed. Hopefully many producers have residual herbicides in place to prevent emergence of kochia.
Figure 1. Newly emerged kochia in the cotyledon stage. This is in an irrigated corn field near Tribune on March 10, 2015. Corn residue was not covering the ground in this area of the field. With no soil-applied residual herbicides present, the kochia emerged. Photos by Curtis Thompson, K-State Research and Extension.
Figure 2. In a different area of the same corn field, residue was moved aside and elongated light-starved kochia have emerged beneath the residue.
Can this emerged kochia be managed adequately at this point? Kochia plants in the cotyledon stage can be controlled with a direct application of a herbicide (provided the kochia population is not resistant to the herbicide being applied). When making an application at this time, the triazines -- atrazine or metribuzin -- an oil adjuvant should be added to enhance postemergence activity. Products containing dicamba will control these small kochia. Products which contain isoxaflutole -- such as Balance Flexx, Corvus, or Scoparia -- with an oil additive and AMS will control small, emerged kochia. Other products such as Sharpen or Verdict with MSO will also control these small, emerged kochia. Even glyphosate will control many of these little kochia at this stage of growth.
But the problem remains with the kochia beneath the residue. These plants will not be covered adequately by an application of herbicide at this time. If dicamba or isoxaflutole products are applied, and if moisture follows the application to incorporate the herbicide, these herbicides can be taken up through the root systems of this little kochia and translocated into the plant and the kochia will be controlled. The PPO herbicides, such as Sharpen products, or Authority/Spartan products, are much less likely to provide control after kochia have emerged.
Figure 3. Dense stand of kochia on March 10, 2015. This can cause severe problems if left uncontrolled.
Figure 4. Kochia in the "fuzzball" stage.
Even a dense stand of small kochia, as in Figure 3 above, likely can be controlled if herbicides are applied soon. Within two or three weeks, the kochia that emerged recently will be in the fuzzball stage (Figure 4) and from that point on the plants will be much more difficult to control. This is especially true in a more stressful environment where the plants are short of moisture and nutrients – which is more likely to occur in a dense stand. Foliar applications of herbicides in mid- or late-April on stressed kochia in a dense stand are often unsuccessful regardless of the herbicide combination used.
Curtis Thompson, Extension Agronomy State Leader and Weed Management Specialist