By: Jason Kelley, Tom Barber, Gus Lorenz, Glenn Studebaker, and Nick Seiter
As we approach grain sorghum harvest, many are considering using a harvest aid. There are pros and cons to using a harvest aid. The greatest benefits are that they can dry down green plant and or weed material to allow quicker, more efficient harvest. Harvest aids can also shut down the plant and prevent late sucker head development, which sometimes can cause harvest issues, especially if sucker heads are allowed to form grain. The downside of using a harvest aid is the risk of applying too early and reducing yield and quality of the grain. Another potential problem is the unknown factor about what the weather will be like two weeks after applying a harvest aid. Once fields have been sprayed with a harvest aid, they should be harvested timely. Delaying harvest due to weather or other unforeseen factors can increase lodging problems, which will reduce yield. Harvest aids are also an added expense that are not always needed. Harvest aids will dry leaves and reduce the green material going through the combine but will have minimal or no impact on actual grain moisture.
This year with sugarcane aphid numbers increasing, many are also considering a harvest aid as a tool for aphid management. Appropriate timing of harvest aids is essential to preserve yield and quality and maximize usefulness of these applications.
Timing of Harvest Aids: Harvest aids should only be applied to mature grain sorghum. At early maturity, grain will be approximately 30% moisture. In evaluating maturity, examine the lower portion of the head, since the kernels at the bottom of the head will be the most immature. If the bottom kernels are still watery, a harvest aid application needs to be delayed until the kernels are more mature. Kernels will develop like corn with a starch line moving from the top of the kernel to the bottom. Once the kernel is mature, a black layer should be evident at the base of the kernel (Figure 1).
Given the wet spring we have experienced, many fields have a range of maturity across a field which makes an appropriate timing more difficult. If large areas of fields are much later in maturity (ie, replanted, or wet areas of fields), applying a harvest aid too early will likely reduce yield and quality in those areas. Figure 2. below,
shows grain sorghum that is not mature enough to apply a harvest aid since the majority of the kernels are green. Figure 3. below, shows heads with grain that is mature from the top to bottom of the head and would be considered mature enough to safely apply a harvest aid if needed.
Products Available to Use as Harvest Aids: Glyphosate and sodium chlorate are the main products used. Aim is also labeled as harvest aids in grain sorghum for desiccation of morningglories and other vines. Gramoxone is NOT labeled as a harvest aid in grain sorghum. In recent harvest aid studies, glyphosate (Roundup Powermax 22oz/A) has provided the best overall kill of the plant, including desiccation of young green sucker heads. Glyphosate has a 7 day pre-harvest interval and once applied, fields can be harvested approximately 10 days after application if grain moisture is low enough. Glyphosate can be applied to grain sorghum that is mature (30% moisture), but I would prefer to apply no earlier than 25% moisture to minimize the amount of time the plant has to stand in the field waiting for the grain to dry.
Sodium chlorate (3qt/A) is applied closer to harvest, generally 5 days prior to harvest and grain moisture needs to be nearing 14% which is considered dry. Hot and dry conditions are typically needed for the best performance of sodium chlorate. There has been no observed benefit in tankmixing glyphosate and sodium chlorate. If vines or other broadleaf weeds are present, tankmix 1.0-2.0 oz/A Aim with the glyphosate application.
Based on experience last year, spraying a harvest aid on grain sorghum with heavy infestations of sugarcane aphids does not control the aphid. In some cases, applying a harvest aid such as glyphosate or sodium chlorate in the presence of heavy aphid populations has caused the aphids to move up into the head. This has the potential to cause harvest issues, including increased time and costs to clean the harvester, mechanical failures, and reduced harvest efficiency. Spraying Transform insecticide with glyphosate last year 14 days prior to harvest worked well. Keep in mind Transform has a 14 day pre-harvest interval, while Sivanto insecticide has a 21 day pre-harvest interval.
Other considerations – If grain sorghum is going to be sprayed with a harvest aid, spray only what you are capable of harvesting in a couple days. You don’t want to spray all of your acreage at once and then it takes 3 weeks to get it all harvested. Once the plant has been killed, it needs to be harvested timely. Last year I saw fields that were sprayed with glyphosate 3 weeks prior to harvest. At harvest they were still standing, but waiting longer would have likely resulted in lodging issues. Once a harvest aid is applied, you are committed to harvesting timely.