Daniel Fromme, Stephenson, Daniel O., Price, III, Paul P
Applying a harvest aid to grain sorghum has become a very common practice in Louisiana. When properly applied, they permit faster and more efficient combining with no reduction in grain weight. Grain moisture content from across the field will be more uniform, which can result in fewer moisture discounts. It is relatively easy to determine the black layer stage of kernel development when harvest aids should be applied. A black layer forms at the seed attachment point at physiological maturity when maximum seed weight is reached. At the black layer stage, the vascular tissue or phloem tubes can no longer carry nutrients and water to grain, and the seed can no longer increase in dry weight.
Grain sorghum producers may consider harvest aids to manage sorghum drydown and harvest because they:
Physiological maturity in grain sorghum is reached when a black layer appears on the sorghum kernels. This layer is visible at the base of the kernel following individual detachment from their outer glume. Physiologically mature seed will contain approximately 30 percent moisture. Sorghum seed change color and accumulate hard starch in a similar manner to maturing corn kernels. If you observe a considerable amount of green seed rather than the red or brown color of mature seed, you will need to wait and give the field more time to fully mature.
Seed at the top of the head will mature prior to those located at the bottom of the head because sorghum pollinates first at the top of the head and progresses steadily downward to the base of the panicle (or flower cluster) in six to nine days. On average, sorghum hybrids reach black layer at 120 days after planting. Most sorghum hybrids reach 50 percent bloom about 75 days after planting, and another 45 days are required after pollination for the grain to reach physiological maturity.
In Figure 1, five kernels of sorghum have been removed from different locations on the seed-head. Kernels 1, 2, 3, 4 and 5 were located in descending order down the seedhead. The crop is considered mature when all the kernels appear like kernels 1, 2, and 3. Kernels 1 and 2 have a fully developed black layer, and kernel 3 has a black layer that has formed. Kernels 4 and 5 show almost no formation of a black layer. Hard starch forms initially at the seed crown and progressively moves toward the base where it develops a black layer similar to corn. Pinch a seed between your fingernails. If you easily penetrate soft dough at the base of the seed, it is not mature.
Do not apply a harvest aid prematurely or before physiological maturity because you will sacrifice yield and reduce test weight by hastening seed fill. About 25 percent seed weight is added during the last 14 days prior to physiological maturity. Therefore, it is extremely important to scout the entire sorghum field and properly determine physiological maturity before applying a harvest aid.
Figure 1. Sorghum kernels in various stages of maturity harvested from the same panicle from the most mature (1) to the least mature (5). The black layer is first visible in kernel 3 and becomes more distinguishable as the seed loses moisture.(Dan Fromme, LSU AgCenter)
Three products are labeled for use as harvest aids: sodium chlorate, glyphosate, and carfentrazone. Good spray coverage is essential for all three products.
This information is provided as a guide only. Always consult the product label or manufacturer for complete information.
Healthy sorghum plants usually do not lodge after a harvest aid is applied and are capable of standing for up to three weeks after treatment. After 30 days, lodging can be significant. It is a good idea to apply harvest aids to only the fields that can be harvested within 14 days of application.
Charcoal rot can cause premature lodging; therefore, it is a good idea to inspect fields before an application is made. Infected plants die prematurely before grain fill is completed (Figure 2). Visual inspection of plants before applying a harvest aid requires splitting the stalk lengthwise. Infected stalks will be soft, spongy, or disintegrated at the crown with charcoal-colored specks, which are fungal reproductive structures. If the stalk is unhealthy, plants will generally fall regardless of treatment. Figures 3 and 4 provide the visual symptomology when charcoal rot is present.
Figure 2. Infected plants die prematurely before all grain can be filled. Upon closer inspection, many sorghum heads will appear dull and lackluster and the spikelets may droop, giving the panicle a ragged appearance. Panicles will contain shriveled grain with the worst being found at the base of the sorghum head, which would have been the last grain to mature. (Tom Isakeit, Texas A&M University)
Figure 3. By the time sorghum begins to lodge, it may be too late to apply glyphosate. When sliced open, the lower 5 to 6 inches of the stalk will be soft, spongy, and/or disintegrated. Within there will be charcoal-colored specks, which are reproductive structures of the pathogen. As prematurely killed plants continue to lose moisture, the plants will fall rapidly under the weight of their own grain. (Tom Isakeit, Texas A&M University)
Figure 4. Harvest aid applications may accelerate the fall of infected plants with charcoal rot. To avoid excessive lodging, harvest in a timely manner. (Tom Isakeit, Texas A&M University)
Stichler, Charles and Steve Livingston. 2003. Harvest Aids in Sorghum (L-5435). Texas A&M University. Online at http://publications.tamu.edu/CORN_SORGHUM/PUB_Harvest%20Aids%20in%20Sorghum.pdf [URL accessed August 2017].