Some high-yielding soybean products have good late season health which can manifest itself in green stems, making them more difficult to harvest.
Use of a defoliant may help dry out the plants faster and allow greater ease of harvest.
There may be other situations in which a defoliant could provide benefits including facilitating the use of fuller season soybeans, improving harvest timing, or increasing odds of cover crop establishment through an earlier harvest.
This research project was designed with a goal of evaluating the impact of defoliant application on soybean yield and harvest timing.
This research was conducted at Bayer Crop Science research sites in Illinois Counties: Adams, Woodford, Stark, Dekalb, and Kendall.
Eight soybean products ranging from 2.7 to 3.8 maturity group (MG) were used, with different products at each location.
Standard fertility and weed management practices were followed.
Defol® 5 (sodium chlorate) was applied at a rate of 4.8 quarts/acre in a 20 gallon/acre carrier volume.
Defoliant was applied at the R6.5 growth stage, which is occurs 7-10 days after R6 and is defined as the timing in which the seed easily separates from the protective membrane within the pod.1
Late September and early October were hot and dry across the northern half of Illinois, leading to quicker than normal soybean maturation.
Plots were harvested as soon as feasible after reaching maturity.
UNDERSTANDING THE RESULTS
There was no negative association between defoliant use and soybean yield (Table 1). Overall, the average yield of the treated strips was 69.2 bu/ acre, while the untreated strips averaged 68.7 bu/acre.
There was no significant difference in moisture between treated and untreated (Table 1). It should be noted that most of the locations were not able to be harvested immediately when maturing, so the grain moistures had time to equalize.
A fairly large range in maturity response to defoliant was observed, ranging from no benefit to 9 days, with an average of 2.4 days earlier (Table 1). This response was probably confounded by abnormally rapid maturation of the soybean crop across the state in 2021.
Defoliant application can be made without negatively impacting soybean yield in situations where it would potentially benefit a grower’s operation.
Benefits to harvest timing may vary based on application time and fall weather.
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/