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Soybean herbicide harvest aids can serve multiple purposes. In some regions, harvest aids are used to desiccate the green tissue (pods, leaves, and stems) on physiologically mature soybean plants to help promote harvest efficiency.1 Harvest aids can help desiccate weeds that may interfere with harvest operations. The potential to provide weed control benefits or reduce weed seed viability is highly dependent on the herbicide used, weed size, and application timing.
Things to consider prior to application of a harvest aid product:1
The advantages of using a harvest aid product include potentially better harvested seed quality, earlier harvest, and/or increased harvesting efficiency. However, an improvement in overall yield potential is not an expectation. Pre-harvest herbicides do not speed up maturity, or make soybean seed dry down faster, they only serve to drop remaining leaves and dry out green material. A harvest aid may facilitate the drying of pods, making them easier to harvest.
Desiccants can reduce green vegetation, but do not remove excessive moisture from the seed. The addition of sodium chlorate to a desiccant can help to remove excessive moisture from green tissue and/or seed, and provide control of weeds. Harvest the desiccated soybean crop according to label.
Weeds that are drought stressed may not be desiccated effectively. Crop and weed drydown may be slowed during periods of cool, wet weather. Additional time beyond the pre-harvest interval may be needed to dry down large weeds.
The commonly used harvest aid products have specific instructions regarding application timing (Table 1). Once soybeans reach the R6 growth stage it is a good time to begin sampling fields in preparation for a harvest aid application. In general, it is advisable to wait until the plants have reached the R7 growth stage, which is when rapid leaf yellowing begins and one or more pods reach the mature brown or tan color.2 Once seeds turn yellow, they begin to separate from the white membrane of the pod, indicating that seed filling is reaching completion and an application may be considered. Application of a product prior to label instructions can reduce seed yield potential or quality. To determine the growth stage of a soybean field, randomly collect pods from the top 1/3 of plants throughout the field and examine the pod and seeds to determine if all of them meet the criteria for an application as specified by the product label.
Herbicides such as Gramoxone® SL, Sharpen® powered by Kixor®, and Aim® EW can be used as harvest aids in soybean. Each product has attributes and products differ in speed of activity, efficacy, pre-harvest intervals, and cropping restrictions. Please check product labels prior to use for recommendations and precautions. Gramoxone SL is a contact herbicide that can provide desiccation of soybean plants and should be applied in at least 20 gallons of water/acre for good coverage. Translocated herbicides, like Sharpen®, are taken up and move through the plant requiring more time for more complete activity. Tank mixtures may provide the best combination of crop desiccation and weed control. Spray adjuvants are typically recommended with harvest aid products to improve coverage and efficacy.
Sources: 1 Heatherly, L.G. 2011. Using harvest aids for soybeans. http:/mssoy.org; 2McWilliams, D.A., Berglund, D.R., and Endres, G.J. 2004. Soybean growth and management quick guide A-1174. North Dakota State University. University of Minnesota. Web sources verified 8/4/2015.