Utilizing harvest aids for grain sorghum has become more popular in recent years. Historically, the crop would be left to terminate and senesce naturally.
The main purpose of applying a harvest aid would be to improve harvest timing. Delayed harvest after the grain becomes mature can potentially reduce grain yields. An exposed crop can experience losses due to pest pressures like bird damage, as well as environmental losses like severe storms with strong winds or hail.
Many factors can delay harvest. Some newer genetics may exhibit characteristics like “stay green” where the plants stay green longer. At harvest, the higher moisture content of the plant can potentially spike grain moisture if combines are not set correctly. If fields have excessive weed infestations, the same concerns of spiking grain moisture at harvest can delay harvest. If stands are on the thin side and growing conditions improve later in the season, the addition of late tillers can become problematic. Unevenness in maturity of a field can also delay harvest.
Preparing the crop for harvest is achieved when harvest aids are applied correctly. Harvest aids in grain sorghum fall into two groups, herbicides and desiccants. The products available have little influence on the grain itself, but work more in the vegetative biomass of the plant. Therefore, these products have little to no direct impact on grain moisture. Glyphosate, carfentrazone and sodium chloride are currently the only three products labeled for use in grain sorghum.
Sodium chloride is a true desiccant and may not kill the crop, but can rapidly dry-down any plant material that it contacts. If not harvested in a timely fashion, plant lodging or regrowth can occur. Glyphosate and carfentrazone are herbicides that, when use as directed, can terminate the crop or weeds. Glyphosate is more widely used, but generally takes longer to shut down the plants. Glyphosate also has a longer pre-harvest interval at seven days, while carfentrazone is only three days. Carfentrazone is a good option to assist with broadleaf weed desiccation and is a great option to tank mix with glyphosate if there is concern of herbicide resistance.
If a producer chooses to have a harvest aid applied, applying the product correctly will greatly affect any potential economic gains. The first component of applying these products correctly involves application timing. A harvest aid should not be applied any earlier than physiological maturity, often referred to as black layer. Applying too early can reduce grain fill which will directly reduce grain yields.
To check for black layer, inspect the base of seeds on multiple plants, tillers of each plant, and locations within each panicle. Delayed plant emergence and late tiller additions will likely be farther behind. Typically, panicles mature from the top down.
Maturity can widely range, so understanding how far along the majority of the crop is will improve proper application timing. Applying too late will not reduce grain yield, but delaying harvest due to labeled pre-harvest timing intervals may lead to losses.
In addition to proper application timing, adequate spray coverage also is an important part in a successful harvest aid application. Apply these products in a minimum of 10 gallon of water per acre when ground applied or a minimum of five gallons of water per acre when aerially applied.
Under certain conditions, like thick canopy of sorghum or weeds, increasing carrier volume up to 15 or 20 gallons of water per acre can increase efficacy of these products.
Harvest aids have no impact on yield potential in sorghum. Since these applications are made after physiological maturity, total yield potential has been set and crop dry-down is the only aspect remaining. Just like other crop protection products, harvest aids will only protect yield potential. A two-year study recently done by Okla
homa State University found yields for sorghum not treated with harvest aids resulted in an average reduction of around seven bushels per acre in north central Oklahoma and just over five bushels per acre in the Panhandle.
More information can be found in the OSU factsheet “PSS-2183 Using Harvest Aids in Grain Sorghum Production” or by visiting your local OSU Extension office.
Bushong is Oklahoma Cooperative Extension Service northwest area agronomy specialist.