Harvest-aid use in grain sorghum

One of the consequences of this year’s drought is the poor head exertion in those fields where the sorghum is producing a harvestable yield. I actually do not remember a time when I have seen such poor head exertion from practically every field I have seen.

Because of this poor head exertion, many growers may want to consider using harvest aid this year. I know no one wants to spend any more money, but a harvest aid may be worth it to speed up harvest and reduce trash in the grain.

The use of a harvest aid should dry out the upper green leaves that are surrounding the head. A second benefit is desiccating any green weeds that may be present. Harvest aids, especially glyphosate, prevent any late tillers from developing grain that could further delay harvest or result in high-moisture grain being delivered to the elevator.

Three products are labeled as harvest-aids for use in grain sorghum: glyphosate, Aim herbicide and sodium chlorate (Defol).

• Glyphosate is the most commonly used product and will kill the sorghum plant as well as many weeds. The product works slowly but does kill the plant, which means the stalk begins to deteriorate. This deterioration of the stalk can lead to lodging if the sorghum is not harvested in a timely fashion. When using glyphosate, treat only the number of acres that can be harvested within a few days of the sorghum being desiccated or killed. The labeled pre-harvest interval is 7 days.

• Aim herbicide is sometimes mixed with glyphosate to facilitate the control of morning glory and other vine-type weeds.

• Sodium chlorate is popular among growers who are producing sorghum for seed production since there is no risk of the product moving into the seed and potentially hurting germination. Sodium chlorate is a quick-acting contact product that dries out the plant (leaves) rather than killing it. If this product is used, growers should be prepared to harvest the crop quickly, prior to any regrowth that may occur. Sodium chlorate is unlikely to kill tillers.

Keep in mind that harvest-aid products do not speed the maturity process of the grain, apply a harvest aid only after the grain has reached maturity. Grain sorghum matures from the top of the head and progresses downward, so check the bottom of the head for grain maturity. Be careful not to apply a harvest aid too early. Approximately 25% of the kernel’s seed weight is filled the two weeks prior to reaching physiological maturity. The grain is considered mature once hard starch has formed at the base of the kernel where it is attached to the panicle branches. A mature kernel will have a black spot at its base.

At maturity, the grain contains between 25% to 30% moisture. A harvest aid can be applied at this time. A common misconception is that a harvest aid will speed up the drying of the grain. This is not the case. Harvest aids will dry out leaves and stalks but have very little impact on grain moisture. For this reason, most agronomists recommend that growers wait until the moisture content is below 20% before applying a harvest aid. Grain drying time will depend on weather conditions.

Another consideration of using a harvest aid in sorghum is the presence of sugarcane aphids. Harvest aids used alone have not been shown to eliminate sugarcane aphids. If the sorghum plant is desiccated or killed, the sugarcane aphids eventually will leave. But, by that time, the window for a timely harvest may be past. If sugarcane aphids are present, it is best to apply an insecticide along with the harvest aid to eliminate aphids and facilitate a timely and efficient harvest. Since sugarcane aphids only need to be controlled for a short period of time, use the lowest labeled rate of product.

For more information, see the excellent publication from Josh Lofton at Oklahoma State University at https://extension.okstate.edu/fact-sheets/using-harvest-aids-in-grain-sorghum-production.html. A second article that provides additional information was prepared by Erick Larson at Mississippi State University at https://www.mississippi-crops.com/2021/08/07/when-is-it-safe-to-apply-a-harvest-aid-to-sorghum/.

Editor’s note: Brent Bean, Ph.D., is the Sorghum Checkoff Director of Agronomy, Lubbock, Texas. For more information visit www.sorghumcheckoff.com.