Harvest Aid Use in Soybeans
Desiccants are commonly used harvest aids to remedy problems that may interfere with efficient soybean harvest. Desiccants can kill green tissue (leaves, stems, pods) on soybean plants and green weeds.
Harvest aid use in Mississippi has become a standard production practice for soybean growers. However, there are a number of points that should be considered before using soybean harvest aids.
• Purposeful desiccation prior to soybean harvest is an option to consider:
• In ESPS plantings in the midsouthern USA where an earlier open canopy allows weed resurgence before soybean maturity and subsequent harvest, and
• When soybean plants have green leaves and stems but pods are mature and ready for harvest.
• A preharvest desiccant will be needed if weed densities are high enough to lead to:
• Increases in soybean seed moisture and damaged soybean seed, and/or
• More foreign material in the harvested seed, and/or
• Decreased combine speed and subsequent decreased harvest efficiency.
A general summary of when to use preharvest desiccants and the currently available products that can be used in this operation are presented here.
Details from a recently completed research project (MSPB Project No. 57-2017) conducted by Dr. John Orlowski provide additional information about desiccation prior to soybean harvest. A summary of the premise for, conduct of, and results from this research follow.
• The commonly used compounds applied as harvest aids in soybeans are paraquat (Gramoxone), saflufenacil (Sharpen), and sodium chlorate (Defol). Each chemical label recommends or states that different adjuvants (e.g. crop oil concentrate [COC], methylated seed oil [MSO], non-ionic surfactant [NIS]) must be used.
• The label for harvest aids specifies a pre-harvest interval (PHI), which is the minimum amount of time that must elapse between chemical application and soybean harvest. Different harvest aids have different PHI requirements that will affect the amount of time a soybean crop is in the field after harvest aid application.
• Studies were conducted at Stoneville, Miss. in 2016 and 2017 to: 1) Investigate the effects of different adjuvants on harvest aid performance; 2) Investigate the effects of spray volume on the efficacy of various soybean harvest aids; 3) Investigate the effects of harvest interval after harvest aid use on soybean yield, seed moisture content, and shattering; and 4) Determine the effect of various rates of paraquat on soybean at multiple growth stages to simulate issues with spray tank contamination and drift.
• Harvest aid products used were Gramoxone, Defol, and Sharpen applied alone or with adjuvants that included either COC, MSO, or NIS.
The following major results and conclusions accrued from this project include the following.
• The harvest aid products used in this study and applied alone did not affect soybean seed yield in either year when compared to each other and the untreated control.
• Yield results from this two-year study indicate that Gramoxone applied alone and with no adjuvant is the best product to use for defoliating soybeans prior to harvest. Overall, Gramoxone applied alone resulted in the most cost-efficient and effective defoliation in both years.
• Yield losses from delayed harvest in this study were not significant until well after the end of the PHI of 15 days for Gramoxone.
• Of the products used in this study, Gramoxone has the longest PHI of 15 days. If this product is applied at the earliest allowed time to prevent yield loss (soybean stage R6.5), then this 15-day waiting period will end at about stage R8 or maturity. Thus, a properly timed application of Gramoxone as a harvest aid will not cause a delay in harvest beyond the time of harvest maturity.
• Be prepared to harvest soybeans as soon after desiccation as allowed by the desiccant label to prevent shattering and subsequent loss of yield since harvest delay past the PHI was associated with a lower yield than that obtained when soybeans were harvested at the earliest possible time in relation to a product’s PHI.
Harvest aids/desiccants can be an excellent management tool to control late-season weeds in soybeans and ensure more efficient harvest. However, they must be used in accordance with the proper soybean stage for their application and the desiccant product’s label.
Composed by Larry G. Heatherly, Aug. 2018, larryheatherly@bellsouth.net