Sponsored: Fall vs. Spring Burndown in Soybeans
In times of lower commodity prices, we’re always trying to find new ways to cut cost. One area to consider is cutting costs on soybeans is your fall burndown program. But, before making that decision, you should evaluate the benefits of a fall burndown.
If pests such as soybean cyst nematode (SCN) are an issue on your farm, a fall herbicide application may be necessary as SCN can overwinter in henbit. These applications will also help control winter annuals such as marestail that have developed resistance to the glyphosate as well as group 2 (ALS) herbicides. Marestail can germinate in both the fall and spring, so a fall burndown can reduce the amount of weeds present at the time of spring burndown. Because marestail can also overwinter as a rosette, it is much easier to control in the fall before it bolts in the spring.
Figure 1: A marestail rosette overwintering (A) compared to a plant in early summer (B)
A fall burndown can also reduce late escapes of summer annuals, preventing them from adding to the soil seed bank. Because there is less vegetation in the spring, a fall burndown can also help warm soil temperatures. Do the benefits of a fall burndown outweigh a spring burndown? We have seen great value with a fall burndown so it’s important to find cost effective treatments that will result in effective control.
Beck’s Practical Farm Research (PFR)® team in southern Illinois is evaluating fall versus spring burndown programs this year in an effort to not only compare the weed control between the two programs, but also find the most effective ways for the two programs to work in unison. For example, if a fall burndown is applied, can a cheaper burndown in the spring such as Gramoxone® or Roundup plus 2,4-D help save on costs? Ultimately, a successful soybean herbicide program begins with a successful burndown. A burndown also provides the opportunity to use different modes of actions as well as herbicide actives. The table below depicts the treatments that are currently being evaluated.
Table 1: Herbicide burndown treatments that will be tested in the fall or spring
When deciding which fall herbicide treatment to use, you must first determine what you want out of your fall herbicide. Do you just want burndown activity? Or do you want residual activity that will last all fall? For just burndown activity, Brash® is a cheap and effective product. However, only the weeds present at the time of application will be controlled, so this product is an effective option to apply after harvest to control any late emerging summer annuals such as waterhemp. Brash could also be effective toward the end of the season when weeds are still actively growing but soil temperatures are on the verge of dropping reducing new flushes.
Products such as metribuzin will provide both burndown and residual activity. However, the residual value won’t be as great as with Autumn™ Super or Classic®. This will cause the residual activity to break by spring, deeming another burndown necessary. Authority® MTZ will result in residual activity for the fall, but if an Authority based product will be used in the spring, a different product should be applied in the fall.
In this study, we are also evaluating various Group 2 herbicides which can provide extended residual activity late into the fall on many winter annuals. However, marestail has developed resistances to many Group 2 herbicides. The success of a fall burndown will influence what is needed in the spring. For this study, fall treatments will be rated in the spring at the time of the burndown application. Gramoxone®, which was selected to help offset the cost of the burndown, will then be applied across all fall treatments and evaluated 28 days after treatment (DAT). Other successful spring treatments that are being tested could be an option if heavy weed pressure is present.
Figure 2: Annual bluegrass (A) and henbit (B)
When it comes to spring treatments, we must first decide if we want just burndown activity or burndown plus residual activity. Products such as 2,4-D can result in cheap, effective burndown activity but will require a plant back restriction. One substitute could be Xtendimax® on Roundup Ready 2 Xtend® soybeans, which would result in no plant back restrictions.
Gramoxone applied in the spring will result in the use of another mode of action compared to the traditional Group 2, 14 and 15 herbicides. However, Gramoxone will result in no residual value. Some options that will result in residual value would be Sharpen®, which is very effective in controlling GR horseweed and summer annuals or Metribuzin which provides effective burndown and residual control. These products will not only provide residual control but will help prevent any new emergence of weeds until planting. Once again, visual ratings will be taken at 28 DAT.
Figure 3: Common chickweed (A) and field pennycress (B)
An effective fall and spring burndown can lay the success of the entire soybean herbicide program. However, as margins become tighter we must find ways to have successful weed control that is also cost effective. This study will look at the positive and negatives of the two different burndown timings. We will also look at how we can make fall and spring burndown work in unison to help save cost. Stay tuned for more insights as this study progresses!
Joe Bolte CCA | Southern Illinois-PFR Operator/Herbicide Specialist
Practical Farm Research (PFR)® is a registered trademark of Beck’s Superior Hybrids, Inc. Brash® is a registered trademark of WinField United. Autumn™ Super and PowerMAX® are trademarks of Bayer. Classic® is a registered trademark of E.I. du Pont de Nemours and Company. Authority® MTZ is a registered trademark of FMC Corporation. Gramoxone® is a registered trademark of a Syngenta Group Company. Sharpen® is a registered trademark of BASF. Xtendimax® and Roundup Ready 2 Xtend® are trademarks of Monsanto.