Benefits of Harvest Aids for Soybean

Key Points

• Soybean fields that have green weeds present, or soybean stems that remain green at harvest time, can negatively affect harvest efficiency, seed yield, and seed quality.
• Soybean stems that remain green after physiological maturity can be a result of environmental stresses, disease or insect pressure, or nutrient imbalances.
• The timing of harvest aid applications is critical. Harvest aids should NOT be applied prior to the R6.5 growth stage.
• Several herbicide options are available to desiccate weeds or green soybean stems and leaves prior to harvest.

Why Should Harvest Aids Be Considered for Soybean Plants?

Soybean fields with an excess of stems and leaves that remain green beyond seed maturation, or which have green weeds present, may benefit from the use of an herbicide or desiccant as a harvest aid. Weed escapes due to a lack of control from pre-emergent and/or post-emergent herbicide applications can result in large weeds that may cause problems for harvesting equipment.

Both green soybean stems and green weeds can interfere with a combine’s harvesting efficiency. This reduction in efficiency occurs because green stems are tougher, more pliable, and more fibrous than dry stems. Green stems can wrap around the combine’s header and threshing components, causing plugging and downtime. When compared to harvesting dry and brittle plant material, a combine requires more power to thresh wet, green plant material, the belts that drive the threshing components can wear out quicker, and the combine will also have more difficulty separating crop residue from the grain if the residue is wet. Green plant matter can also increase the amount of foreign material in the harvested soybean seed, possibly resulting in dockage at the grain terminal or a reduction in seed quality.^1,2,3

What Causes Green Stems in Soybean Plants?

The causes of green stems (Figure 2) and/or green leaf retention (Figure 3) in soybean after physiological maturity—sometimes referred to as green-stem syndrome (GSS)—can be complex but are often attributable to some combination of drought, excessive rainfall, nutrient imbalances, insect or disease pressure, or genetic tendencies.

Late season rain following an extended period of drought can sometimes cause soybean to “green up” prior to maturity by retaining green leaves and stems longer than if adequate soil moisture had been readily available through most of the growing season. This may be due to a disruption of normal growth creating an imbalance in the sink-source relationship within the soybean plant. Low pod production caused by drought may result in less demand for photosynthetic products within the plant, thus trapping them in the stems and causing the stems to remain green. A good illustration of this can occur when the non-irrigated “corners” of center pivot irrigated fields are drought stressed mid-season, but recover following late season rain and then remain green while the irrigated portion of the field is ready to harvest after the leaves have dropped and the stems dried down normally.

Viral diseases, such as bean pod mottle, have been linked to green stems. Insect feeding by stinkbugs, bean leaf beetles, aphids, or thrips may also contribute to stems remaining green. The application of foliar fungicides, specifically strobilurins, may enhance green stems due to their added “greening effect.”

Utilizing harvest aids can help promote uniform defoliation and desiccation, which may be desirable since leaving a soybean crop in the field beyond physiological maturity while waiting for drydown of the green material to occur may expose the crop to adverse environmental conditions that can reduce yield and grain quality.³

Preharvest Desiccant and Weed Control Product Options for Soybean Plants

The primary intent of preharvest herbicide treatments is to control and desiccate weeds that can interfere with harvesting efficiency, and to potentially reduce weed seed production for following years. Preharvest herbicide treatments will not speed up crop maturity. Growers must balance the benefits of faster desiccation and leaf drop from contact herbicide products (e.g., paraquat), which may not result in a complete kill of the weed, versus a potentially more effective control from systemic products such as glyphosate that may require more time to achieve the desired outcome. Preharvest treatments with systemic herbicide products can also provide an opportunity to manage warm season perennial weeds. Weeds such as marestail, waterhemp, Palmer amaranth, or giant ragweed will likely not be controlled by glyphosate; therefore, dicamba may provide a better option.²

Paraquat, alone or in a permissible tank mix with saflufenacil or sodium chlorate, is commonly recommended for harvest aid applications. Carfentrazone-ethyl, along with glyphosate and dicamba, which were mentioned earlier, provide additional options for harvest aid (Table 1). While both saflufenacil and sodium chlorate may be applied alone, this is not often recommended. Additionally, keep in mind that sodium chlorate is a true desiccant, which can rapidly pull moisture from plant material. While this may be advantageous in improving harvest efficiency, it can also lead to pod shattering if harvest is unnecessarily delayed post application.³ It is recommended to delay application of sodium chlorate if rain is predicted to occur in the next several days.

Table 1. Examples of herbicides labeled for use as a soybean harvest aid.*

Harvest Aid Application Timing and the Effect on Soybean Yield

The timing of a harvest aid application is critical because applying too soon can lead to a reduction in yield potential as well as seed quality. Growth stage R6.5, when the pods are turning yellow and the wall membrane inside a pod from one of the four uppermost internodes is separating from the seed, is considered to be the earliest “trigger” time for application. Some experts recommend R6.5 + 3 days in order to ensure that the entire field is at the proper stage and a yield penalty will not be incurred due to applying too early.^3,4,5 By the R7 growth stage, at least one normal sized pod has turned brown, tan, or tawny (Figure 4) and the plant is approaching physiological maturity.

A study published in Agronomy Journal evaluated the effect of harvest aid use on soybean seed yield, protein, and oil content. Data was collected at 19 sites across 13 states. The researchers found that harvest aid applications made at the R7 growth stage rarely impacted seed yield and did not reduce the protein or oil content of the seed. Green stem incidence was reduced 50% of the time and harvest could take place earlier. Yield reduction did occur in some locations when the harvest aid was applied at growth stage R6.5, supporting the recommendation that harvest aid products should not be applied prior to that growth stage.⁴

Research at the University of Arkansas found that the earliest growth stage in which no statistically significant yield reduction occurred was R6.5 when paraquat 3.0 (4.134 lb paraquat cation per gallon) was applied at 10.67 fl oz/acre, compared to the untreated control. Yield reductions of 68% and 56% occurred when paraquat was applied at growth stages R5.5 and R6, respectively. Applications made at growth stage R7 and at 50% leaf drop had a slight yield increase compared to the untreated control. This data also indicated that no statistically significant yield differences were found among various herbicide treatments when applied at the R6.5 growth stage.⁵

Summary

Harvest aids can improve harvest efficiency, especially when fields are infested with weeds or if green stems are still present after the soybean crop matures. The amount of foreign material in the harvested seed can be reduced and seed quality maintained with a properly timed harvest aid application. However, that proper timing is critical to maintaining yield potential while also improving harvest efficiency.

Always be sure to read and follow label instructions for any product being considered for use as a harvest aid.

Sources

¹Jhala, A. 2022. Harvest aid herbicide options in soybean. University of Nebraska–Lincoln Extension, CropWatch. https://cropwatch.unl.edu/2020/harvest-aid-herbicide-options-soybean/
²Loux, M. 2022. Preharvest herbicide treatments for weed desiccation. Ohio State University Extension, C.O.R.N. Newsletter. https://agcrops.osu.edu/newsletter/corn-newsletter/2022-28/preharvest-herbicide-treatments-weed-desiccation
³McNeal, J. 2023. Harvest aid for soybean. University of Tennessee, UTcrops News Blog. https://news.utcrops.com/2023/08/harvest-aid-for-soybean/
⁴Kendall, M.A., Mourtzinis, S., Lindsey, L.E., et al. 2025. Harvest aid applied at soybean growth stage R7 rarely impacted seed, protein, or oil yield. Agronomy Journal. 117(4): e70109. https://acsess.onlinelibrary.wiley.com/doi/10.1002/agj2.70109
⁵Ross, J. and Barber, T. 2025. Harvest aid products and timing in soybean. University of Arkansas, Division of Agriculture Research & Extension, Row Crops Blog. https://arkansascrops.uada.edu/posts/harvest/soybean-harvest-aids-2025.aspx
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