One of the first steps to a successful herbicide program is starting clean to allow the pre-emerge herbicide to reach the soil surface. The burndown also allows the opportunity to utilize other “effective” sites of action (SOA) that can’t be used in-season such as Gramoxone® SL 2.0. Spraying early in the spring provides the opportunity to control winter annuals like marestail and emerging summer annuals such as giant ragweed. When evaluating spring burndown options, we must consider if the herbicide has burndown only activity or burndown plus residual activity. Products like Liberty® and Gramoxone SL 2.0 will not have any residual activity but will provide very effective burndown activity. Other burndown products such as Sharpen® or metribuzin will provide residual value depending on the herbicide rate.
With limited windows for field activity in the spring, finding time to spray a burndown may be limited. If planting is delayed after the burndown application, new flushes of weeds can appear. Therefore, starting clean is the most ideal situation to ensure the pre-emerge herbicide reaches the soil surface. If you’re dealing with new flushes of weeds when the pre-emerge application is applied, some pre-emerge herbicides like Fierce® MTZ and Valor® XLT will have residual and burndown activity. However, when facing marestail or other problematic weeds, the addition of a non-selective burndown herbicide can help increase control of emerged weeds.
BECK’S PRACTICAL FARM RESEARCH (PFR)® RESULTS
In 2020, Beck’s PFR conducted a study that tested burndown products with and without residual activity. This study also looked at pre-emerge herbicides with the addition of a burndown product. Burndown only products such as Gramoxone® SL 2.0 struggled in comparison to other burndown options. However, the addition of metribuzin increased the burndown activity on marestail while also providing residual activity against problematic weeds like waterhemp. Liberty® was also an effective burndown, but should be avoided if used in-season. Enlist One® plus glyphosate was very effective on marestail rosettes, but control decreased once the plants began to bolt.
Burndown products like Sharpen® provided very effective burndown activity and residual control. Adding Liberty or Sharpen to Enlist One added another “effective” SOA and greatly increased marestail control. For residuals, the addition of non-selective herbicides helped increase burndown control. Burndown products with no residual value controlled emerged weeds, but failed to provide future protection. In that scenario, if planting is delayed, new flushes of weeds could emerge. Adding a burndown herbicide to the pre-emerge herbicide would increase control of emerged weeds.
In conclusion, the addition of Liberty or Sharpen to Enlist One increased marestail control and added another “effective” SOA. Sharpen is very effective on marestail and provided residual value to other problematic weeds like waterhemp. Gramoxone SL 2.0 required the addition of metribuzin to provide effective marestail control. Pre-emerge herbicides like Valor XLT and Fierce MTZ provide longer residual activity against problematic weeds other than marestail, such as waterhemp. Some burndown products will have plant back restrictions.
What about dicamba? To learn about utilizing dicamba for a marestail burndown, visit bit.ly/burndown-video
Additional Resources: Download Beck’s 2021 Recommended Soybean Herbicide Program Guide at beckshybrids.com/Herbicide-Brochure
Weed Management Resources under the Agronomy tab at BecksHybrids.com
~ Joe Bolte, M.S., CCA – PFR Technician and Herbicide Specialist