Q: Why is it important to apply a late burndown herbicide when an early burndown application is missed? What are the major limitations?
Weeds grow quickly. If allowed to get a head start, they will grow alongside your crop and compete for resources like sun and water. This creates a competitive advantage for the rest of the season.
A major limitation of late burndown applications is that weeds can be larger and more difficult to control. Growers may need to increase burndown herbicide rates, or use more aggressive herbicide mixtures to achieve better control. Herbicide plant restrictions can be another limiting factor of late burndown applications. This affects decisions like which herbicides to use and the decision to plant as soon as possible.
Q: Why not just wait and spray after planting to avoid any further delay?
If possible, it is better to apply late burndown herbicide before the crop is planted. Weeds can be injured by the planting operation, which requires time to recover before spraying. Weather can quickly change after planting and prevent a post-plant application, allowing existing weeds to negatively impact the crop.
Planning burndown herbicide applications after the crop is planted can be risky. It’s easy to become preoccupied with other operations and weeds only become harder to control with further delays. The risk of crop injury can also increase from some herbicides used in the burndown application.
Q: Why is it important to scout fields before performing late burndown herbicide applications?
Fields should be scouted to observe the weed spectrum and size. This helps growers determine the right burndown herbicide program. In general, winter annual weeds, which are often the focus of early burndown herbicide applications, will already be setting seed with a late application. The focus may switch to summer annual weeds like common lambsquarter, common ragweed, velvetleaf and pigweed species. Also, it’s important to have a plan to control herbicide-resistant horseweed (marestail), waterhemp and Palmer amaranth. At this time, horseweed may be 6-8 inches tall, and waterhemp and Palmer amaranth may begin to emerge. The burndown herbicide program plays an integral role in controlling the most difficult-to-control weeds in the field.
Q: Can growth regulator herbicides be used in late burndown applications?
When using 2,4-D and dicamba, always keep the label precautions and plant back restrictions in mind. When using 2,4-D, soybean planting must be delayed at least 7 to 15 days depending on the rate of application. When using dicamba, soybean planting must be delayed 14-28 depending on the rate of application. An inch of rainfall is required after application before planting can occur. These restrictions can be avoided when planting 2,4-D or dicamba-tolerant soybeans. Also, using approved growth regulator herbicide products in the burndown application can help avoid these restrictions.
Q: How can you control glyphosate-resistant horseweed, giant ragweed and generally big weeds in soybeans with late burndown herbicide applications?
Growers can increase the rate of glyphosate in the burndown application to help control larger weeds. For immediate planting after a late burndown application, using XtendiMax® herbicide with VaporGrip® Technology, a restricted use pesticide, in the Roundup Ready® Xtend Crop System is the best option for managing glyphosate-resistant weeds. Herbicide products that can be tank mixed with XtendiMax herbicide can be found at www.xtendimaxapplicationrequirements.com.
Additionally, a burndown program that includes a residual herbicide can provide extended weed control, as well as multiple sites of action for managing resistant weeds. Residual herbicides can help improve controlling weeds with an extended germination period, like giant ragweed, waterhemp and Palmer amaranth.
Q: What are the weed control considerations when making late burndown herbicide applications in corn?
There are more herbicide choices and flexibility for effective weed control in corn than soybeans. Late burndown herbicide applications in corn can be very effective and safe to the crop. Dicamba and 2,4-D can be used around the time of corn planting. Emerged corn has tolerance to these herbicides. Residual herbicides like atrazine and mesotrione can provide good coverage on emerged weeds. Further, there are numerous postemergence herbicide options available depending on the weed spectrum growers wish to control.
Benefits and Limitations of Early Burndown Herbicide Applications
Hager, A. 2019. Weed management reminders in a wet spring. University of Illinois. The Bulletin.
Loux, M. 2019. Adapting burndown herbicide programs to wet weather delays. Ohio State University Extension.
Burns, E. and Sprague, C. 2019. Weed control recommendations for late and prevented planting. Michigan State University Extension.
Steckel, L. 2019. Late burndown in corn. University of Tennessee Extension.