Kochia control in corn and grain sorghum
Lumax EZ and Lexar EZ, 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.
Control in grain sorghum
There are fewer herbicide options for controlling kochia in grain sorghum than in corn, although there is a wider window available for sorghum than corn to make burndown applications prior to planting. Grain sorghum is planted later than corn, allowing more flushes of early-emerged kochia to be controlled with burndown treatments. Effectiveness of control during this time period is essential as in-crop options become limited.
This later planting of sorghum relative to corn requires producers to make two burndown applications of glyphosate-plus-dicamba before planting. This will control the largest two flushes of kochia emergence of the season. Producers who take advantage of this opportunity often have very good kochia control, although glyphosate-resistant kochia could complicate the issue. Producers who try to cut corners and do not control the early flushes of kochia when they have a chance often have problems with kochia in their sorghum later in the season.
To get the best control of kochia with the burndown treatments of glyphosate and dicamba, the kochia should be sprayed when plants are 2 to 4 inches tall and actively growing. Kochia plants one inch tall or less that have not started to elongate and plants taller than six inches often are more difficult to control, especially under conditions of environmental stress.
If a flush of kochia emerges close to the time of grain sorghum planting, producers could combine a burndown treatment with a preemergence herbicide such as a chloroacetamide/atrazine premix, Lexar EZ, or Lumax EZ. Another option for burndown and early season residual control of kochia prior to emergence of sorghum would be Sharpen or Verdict. Sharpen provides no grass control. Methylated seed oil should be added to Sharpen for optimal burndown activity. Sharpen can be used at the 2 oz rate in sorghum. Verdict would provide some residual grass control. However, at the 10-oz rate, it should be combined with G-Max Lite or Guardsman Max for improved residual weed control.
If a flush of kochia reaches 4 to 6 inches in height and grain sorghum planting is still a week or more away, producers should strongly consider making a burndown treatment before sorghum planting while the kochia is controllable, and then making the preemergence application as a separate treatment.
If a postemergence application becomes necessary in grain sorghum, good options include Huskie+atrazine+AMS, dicamba+atrazine or Starane-containing products. If Starane is used, it would be best to add a half-pound of atrazine.