Statewide
Chemical labels for the use of 2,4-D and dicamba herbicides (e.g., Banvel, Clarity) stipulate specific growth stages, either as leaf number or height of the plant, for application. Both families of growth regulator herbicides have a reputation for potential injury on grain sorghum that can damage grain yield if applications are made at the wrong time, or too much of the herbicide contacts the plant, especially if it gets down in the whorl.
2,4-D (amine or ester formulations): Apply when grain sorghum is 6-15” tall (some labels say 5-15”), but if sorghum is 8” or taller, use drop nozzles to minimize chemical application to the plants.
Dicamba: Apply in the “spike” stage (meaning all sorghum emerged) but before 15” tall (and especially at 3-5 leaf stage—when determining the leaf stage, count the rounded-tip coleoptile leaf as leaf 1, and all subsequent leaves that have a collar, meaning the leaf is fully expanded). Use drops for grain sorghum ≥ 8” tall.
It is difficult sometimes to equate leaf stage and sorghum plant height. Leaf stage is more defined. The main consideration is that the growing point by about leaf stage 6 to 7 is now at the soil line and beginning to move up the stalk. In my experience, I equate leaf stage with about 8” tall. That growing point is very sensitive to these growth regulator herbicide applications! In fact, one former Kansas State University agronomist colleague told the Sorghum U attendees in January that 2,4-D is an inexpensive way to hurt your grain sorghum.
Summary Tips
- Be sure to follow label directions.
- Because of the sensitivity of grain sorghum to 2,4-D and dicamba applications, re-read the section of your label on the timing and growth stage for using these herbicide applications.
- If you are having doubts about whether you should still spray either of these herbicide families in grain sorghum, I suggest you don’t do it. This injury potential IS very real.
- If someone else is making spray applications for you, but you are close to the label restriction when to apply, ensure that your applicator doesn’t “get to it later” or “wait until next week,” and be willing to tell them it is too late and stop the planned application.
- If you believe you should not use either of these chemicals—growth stage too advanced, or you are simply risk-averse with these chemicals—consult your chemical dealer or Texas A&M AgriLife weed specialist for alternatives.
