Harvest Aid Products for Soybeans

What to Know About Harvest Aid Application

When soybean fields remain green beyond seed maturation or have green weeds, the soybeans may require a “harvest aid” or desiccant (Figure 1). In some situations, applying a harvest aid can help increase harvest efficiency, reduce the occurrence of foreign material in the harvested seed, maintain soybean seed quality, and reduce weed foliage.¹

Desiccants promote premature leaf drop and drying of green tissue but do not speed crop maturity or make seed dry faster. The addition of sodium chlorate to a desiccant can help remove moisture from green soybean tissue, including seed, and provide additional weed management.

Figure 1. Soybean fields with large escaped weeds may need a desiccant to accomplish a timely harvest. Weed management exercised early to midseason with labeled herbicides can help avoid the weed growth seen here.

Roundup^® brand agricultural herbicides include Roundup PowerMAX^® herbicide, Roundup PowerMAX^® II herbicide, Roundup PowerMAX^® 3 Herbicide and Roundup WeatherMAX^® herbicide. Each herbicide product is labeled for preharvest applications to soybean plants (both conventional and glyphosate-resistant) once pods have set and lost their green color. The herbicide label must be followed for application timing as it relates to soybean maturity. In addition, the minimum number of days between herbicide application and harvest is an important factor and must be adhered to.

Seven days is the minimum amount of time for when these four Roundup brand agricultural herbicides are applied to conventional or non-glyphosate-resistant soybean plants, and 14 days is the required amount of time if the herbicides are applied to soybean plants with Roundup Ready^® Technology or Roundup Ready 2 Yield^® Technology. Restrictions also apply for the feeding or grazing of grain, hay or fodder.

Application Timing

As you’ve read above, Roundup brand agricultural herbicide labels indicate applications cannot occur until pods have set and lost all green color. This coincides closely with the R8 growth stage (95% of the pods have lost green color and occurs about five to 10 days before the field is ready for harvest).²

Glyphosate products are systemic. As a result, susceptible weeds and conventional soybean products (without glyphosate resistance) may not drop leaves for several days. Glyphosate-resistant soybean products are also not affected by glyphosate herbicides.

For the best harvest aid effectiveness, tank mixes of labeled herbicides should be considered in accordance with label instructions. Table 1, below, provides information about Roundup brand agricultural herbicides including preharvest application timing, rates, days before harvesting after an application, and grazing or feeding restrictions.

Labels for other herbicide products have similar restrictions which must be read for application requirements and may include contact herbicides which kill the tissue the herbicides land upon. The activity of non-systemic herbicides is often quicker than systemic alternatives. However, spray volume may need to be increased to help provide adequate plant coverage. These herbicides are likely to have activity on conventional and glyphosate resistant soybean products. For the best harvest aid effectiveness, reference tank mixes of labeled herbicides.

The best practice is to begin sampling fields when soybean plants reach the R6 (full seed) growth stage. The R6 growth stage is characterized by a pod containing a green seed that fills the pod capacity at one of the four uppermost nodes on the main stem.³ Verification of growth stage can be confirmed by randomly collecting pods from the top one-third of plants throughout the field to determine pod coloration and seed development within the pods. The R7 growth stage is characterized by one main stem normal pod reaching its mature pod brown or tan color.³ When seeds turn yellow, they begin separating from the white membrane of the pod, indicating that seed filling is reaching completion and a harvest aid application may be considered as a solution.

Weed Management

When harvest time comes, improper weed management can cause a slew of problems on top of reduced yield. Did you know research at Mississippi State University showed that even low weed populations at harvest had the potential to reduce combine and cylinder speed? In addition, the amount of foreign material doubled, the percentage of damaged seed increased, and soybean seed moisture increased compared to weed-free control plots.⁴

Many weeds that can be found in near-maturity soybean fields can have mature viable seeds. As a result, if applied preharvest herbicides cause adversely large weeds to die and drop leaves, then the seeds that drop to the ground or run through a combine can grow. Cleaning harvest equipment can also prevent the spread of unwanted weed seed from field to field. Weed competition should be addressed early in the season to help protect crop yield potential and beat back the spread of weeds.

Harvest and Livestock Feeding

Remember: The minimum number of days prior to harvest or preharvest interval after a preharvest application must be followed. Additionally, grazing may or may not be allowed depending on the herbicide. These restrictions appear in the respective labels.

Table 1. Harvest aid herbicides. Herbicide labels must be reviewed and followed.

Sources

¹Heatherly, L.G. 2015. Using harvest aids for soybeans. Mississippi Soybean Promotion Board (MSPB). https://www.mssoy.org.

²Davis, V.M. 2012. A review of glyphosate use for preharvest weed control. Integrated Pest and Crop Management. University of Wisconsin-Madison. https://ipcm.wisc.edu/blog/2012/09/a-review-of-glyphosate-use-for-preharvest-weed-control/.

³Koger, T, Catchot, A., Allen, T., Zhang, L., Eubank, T., and Blessitt, B. 2010. Guide to soybean growth stages. P2588. Mississippi State University. https://www.mssoy.org/ .

⁴Ellis, J.M., Shaw, D.R., and Barrentine, W.L. 1998. Soybean (Glycine max) seed quality and harvesting efficiency as affected by low weed densities. Weed Technology 12(1): 166 - 173. doi:10.1017/S0890037X00042743. Cambridge University Press.

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