The Utility of Fall Herbicide Applications

In the Sept. 22-28, 2015 (2015-31) edition of The Ohio State University’s C.O.R.N. Newsletter, Dr. Mark Loux has penned some informative thoughts in an article entitled “Fall Herbicide Applications and New Technology.” He addresses fall herbicide treatments relative to Enlist (tolerant to 2,4-D and glyphosate) and Xtend (tolerant to dicamba and glyphosate) technologies for those who have decided that fall treatments will no longer be necessary because of the ability to use 2,4-D and dicamba in postemergence treatments. A summary of his points follow.

• Fall herbicide treatments may still be the best option for no-till producers who don’t want to deal with a lot of weed cover in the spring. Also, spring burndown treatments may not control and desiccate weeds fast enough in a no-till system, since these weeds will have had several months to become established and grow.


• Fall is the preferred time to control biennials and cool-season perennials since spring and/or summer treatments with 2,4-D and dicamba may not be as effective for their control.


• Variability of weed control with spring-applied 2,4-D/glyphosate may lead to more control problems than if herbicide applications are made in the fall.


• One or more POST applications of Enlist Duo in addition to an earlier spring burndown application that may have been made means that two or more applications of this same herbicide will have been made, and this could lead to development of 2,4-D resistance. Thus, applying herbicides with a different mode of action (MOA) in the fall should aid in avoiding resistance development to 2,4-D. The same can be said for dicamba use in the Xtend system.


• Using the Enlist and Xtend systems means that 2,4-D and dicamba will be available to use POST in soybeans in addition to their already being applied in fall and spring weed control programs. This overuse will certainly lead to selection for resistance development. So again, using fall-applied herbicides or residual PRE herbicides with a different MOA can offset this overuse of 2,4-D and dicamba that can occur with their availability for POST applications.


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The bottom line is this: Both 2,4-D and dicamba have been used for fall and spring weed management for some time. Now, both the Enlist and Xtend systems extend the use window of 2,4-D and dicamba, respectively, into the summer. This potential overuse of these two herbicides will most certainly hasten selection for resistance in targeted weeds. Therefore, fall and early spring application of herbicides with MOA’s different from that of these auxin herbicides will prolong the effectiveness of these new technologies that are now available for POST weed control in soybeans.

Hopefully, we have learned what over-dependence on a single herbicide/mode of action can lead to in the weed management arena, and can use that knowledge to prolong the effectiveness of these new herbicide technologies that are just now coming on the scene.

Composed by Larry G. Heatherly, Oct. 2015, larryheatherly@bellsouth.net