Soybean cultivar selection in the Mid-southern U.S. has shifted toward early maturing, indeterminate maturity group (MG) 4 varieties. This shift has increased the adoption of harvest aid application in these environments. Leaf retention and green stems and pods in earlier maturing, indeterminate varieties after physiological maturity can delay harvest. Application of harvest aids also assists in late-season weed control and may allow producers to achieve earlier crop delivery at an above-base premium.
Historically, harvest aids in agricultural production systems have been utilized to desiccate weeds and increase harvest efficiency.
Utilizing harvest aids in a soybean production system to promote uniform defoliation and desiccation is a relatively common practice. Leaving a soybean crop in the field beyond physiological maturity may expose the crop to adverse environmental conditions that can reduce yield and grain quality. However, harvest aids in a soybean production system have not been widely adopted in Tennessee.
When handled properly, harvest aids can improve harvest efficiency and promote a timelier harvest.
The three main materials that are used as soybean harvest aids are paraquat, saflufenacil (Sharpen), and sodium chlorate. While each of these three materials are labeled for use as a harvest aid in soybean, they are not necessarily interchangeable.
0.25 lb. ai.
paraquat + Sharpen
0.25 lb. ai. + 1.0 fl. oz.
paraquat + sodium chlorate
0.25 lb. + 3.0 lb. ai.
6 lb. ai.
1.5 fl. oz.
*surfactants per label recommendations
Nearly all harvest aid applications should include paraquat at 0.25 lb. ai. (10.7 fl. oz. of Gramoxone SL 3.0). However, it may also be tank-mixed with Sharpen (saflufenacil) or sodium chlorate. While both Sharpen and sodium chlorate may be applied alone, this is not often recommended. Additionally, understand that sodium chlorate is a true desiccant. This means that is rapidly pulls moisture from plant material. While this may be advantageous, it can also lead to pod shattering if harvest is unnecessarily delayed post application.
Accurately timing a harvest aid application is critical as a premature application will reduce yield. As with irrigation termination decisions, R6.5 is the determining growth stage for triggering a harvest aid application. We want the pod wall membrane to easily separate from the seed prior to application.
We terminate irrigation for soybean at R6.5 with adequate soil moisture in the profile (meaning at least 3 days of moisture remaining in the soil). For application of harvest aids, my rule of thumb is R6.5 + 3 days. This will help ensure that the entirety of the field is truly at R6.5 and that we do not incur a yield penalty for desiccating too early.
Pulling the trigger on a harvest aid is firing a bullet that we don’t get back and means you are committed to having a combine in the field within ~2 weeks. Do not neglect to factor in the weather forecast when considering applying a harvest aid. This applies less to the efficacy of the application and more to the timeline of returning to the field with a combine.
A weather event that does not delay harvest is unlikely to cause any additional damage to the grain. However, desiccating a field that is then exposed to a weather event that prolongs the time to when the field is harvested is a situation we want to avoid.
Harvest aids are sometimes implicated with damage to the grain. However, harvest aids do not directly damage the grain. It is only when application timing is off that any reduction in yield or damage occurs.
Applications prior to R6.5 can absolutely reduce yield. Additionally, desiccating a field that is then exposed to significant rain fall or moisture that delays harvest can result in a reduction in grain quality.
However, with proper application timing, any observed issues with grain quality following application of the harvest aid were likely present prior to the application. In this case, harvest aids do not induce grain damage, they merely reveal what was present to begin with.
Depending on weather patterns and air temperature, the transition from R6 (full seed) to R6.5 can happen seemingly overnight. An effective strategy for successfully employing harvest aids requires a close eye on fields. It also means being able to confidently distinguish between R6 and R6.5, avoiding major weather events post application, and a timely harvest.
10.7 fl. oz. of Gramoxone SL 3.0 + nis (0.25% v/v) is my leading recommendation.
Please do not hesitate to reach out with any questions you have.