In southern soybean growing regions where indeterminate soybean varieties are planted, the pods can physiologically mature while the plant remains green. In those areas, a desiccant is commonly applied near the desired harvest time to hasten plant maturation. Chemicals commonly used for this purpose include paraquat, safluenacil, and sodium chlorate. The herbicides provide an additional benefit of managing weeds prior to harvest, while sodium chlorate (Defol 5) only dries out plant tissues.

Farmers have wondered if this practice could potentially have value in Illinois for multiple reasons. Potential benefits include improving ease of harvest by drying down plants more quickly or minimizing green stem. A desiccant could also help offset delayed maturity brought on by fungicide application. Additionally, harvesting a few days earlier could potentially lead to more successful cover crop establishment. Another possible benefit would be greater yield potential through the ability to plant a fuller season variety while still being able to harvest in the typical timeframe for the area. With all of this in mind, we designed an experiment to evaluate the use of soybean desiccants in north central Illinois.

We chose Defol 5 for this research since weeds were not a problem in the fields being evaluated and to avoid the PHI required for the other products. In 2021, eight soybean varieties were planted across five locations, with a different set of varieties at each location (table 1).

Table provided by Jason Carr, Bayer Crop Sciences

We applied 4.8 quarts/acre of Defol 5 in a 20 gallon/acre carrier mixture at the R6.5 growth stage. The R6.5 growth stage typically occurs 7-10 days after R6 and is defined as the timing in which the seed easily separates from the protective membrane within the pod¹. Growers considering the use of a desiccant must be sure to apply at the proper timing, since applying too early can reduce yield. We learned this in 2020 when we reduced yield by 10-12 bushels by applying at the onset of the R6 growth stage.

In 2021 however, when the desiccant was applied after R6.5, we did not see yield reductions. You can see this in table 2.

Table provided by Jason Carr, Bayer Crop Sciences

At the Newark and Liberty locations the application was later than ideal, coming after plants had reached the R7 stage. As you may remember, the soybean crop matured abnormally quickly in 2021. Thus, we likely did not capture the full potential benefit of the desiccant application as measured by how many days earlier we were able to harvest. In the fields which were able to be harvested earlier, the benefit ranged from one to nine days.  Maximum benefit is reached when the application is made immediately on reaching R6.5.

This research shows that desiccant application has the potential to facilitate easier and earlier harvest without reducing yield. It is also obvious that timing and weather conditions are very important factors. If you feel like this practice is something that could provide benefits to your operation, I’d encourage you to give it a try. You can also feel free to reach out to me for more information about what we learned –  jason.carr@bayer.com.

Sources:

¹Irby, T., Allen, T., Bond, J., Catchot, A., Gore, J., Cook, D., Krutz, J. Golden, B., 2016. Identifying late season soybean growth stages. Mississippi State University Extension. https://www.mississippi-crops.com/2016/08/19/identifying-late-season-soybean-growth-stages/