Harvest-Aid Use in Grain Sorghum
By Sorghum Checkoff Agronomy Director Brent Bean, Ph.D.
The use of harvest-aid products is a common sorghum management practice in the South and Mid-Atlantic States, though the practice is used sparingly in the High Plains. The High Plains usually can rely on a hard freeze to kill the plant and facilitate harvest.
Many of the new dryland sorghum hybrids have more of the stay-green trait which is great for post flowering drought tolerance but does slow down drying of leaves prior to harvest. The use of a harvest-aid will desiccate the green sorghum plant along with any weeds that may be present. Harvest-aids also prevent any late tillers from developing grain that could further delay harvest or result in high-moisture grain being delivered to the elevator. In addition, by using a harvest-aid, the grain sorghum can be harvested earlier — prior to wet conditions that may lead to moldy grain or even pre-harvest sprouting. And finally, harvest efficiency can be improved resulting in cleaner grain, especially under those conditions when the sorghum heads are not sufficiently above the top leaves of the plant.
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. Therefore, 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 14 days.
- Aim herbicide sometimes is 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 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.
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 percent of the kernels 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 and 30 percent 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 percent before applying a harvest aid. Grain drying time will depend on weather conditions.
Another consideration in 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 Dr. Josh Lofton at Ok-State: Using Harvest Aids in Grain Sorghum Production. A second article that provides additional information was prepared by Dr. Erick Larson at Mississippi State: When is it Safe to Apply a Harvest Aid in Sorghum.