How to handle clean no-till bean fields

Soybean Pest Beat: The temptation may be to skip the burndown treatment if fields sprayed last fall are clean this spring.
Tom J Bechman | Mar 05, 2018
I applied herbicides last fall on cornstalks going to no-till soybeans this spring. Those fields are clean as spring approaches. Can I skip the burndown herbicide trip? My worst weeds are typically marestail and giant ragweed in those fields.
The Indiana certified crop adviser panelists answering the question are: Gene Flaningam, Flaningam Ag Consulting LLC, Vincennes; Greg Kneubuhler, G&K Concepts, Harlan; and Tom Stein, Templeton/Boswell branch manager for Ceres Solutions Cooperative.
Flaningam: Skipping spring herbicide application will depend on your herbicide program and what type of herbicide-tolerant soybeans you’re planting. Marestail can’t be rescued in a glyphosate-type soybean herbicide program. Dicamba and Liberty soybean herbicide programs would work well in this situation.  Pay close attention to the label and the size of the weed you are targeting [when you’re ready to spray].
Kneubuhler: Unfortunately, the answer is an emphatic “no.” With fall applications of herbicides, we often start out the spring very clean, and yes, it even looks like we don’t need a burndown trip. I would highly advise against ignoring your spring trip. Fall applications are a great way to start clean and stay clean. However, if you avoid the spring residual pass, you typically pay for that dearly as the season unfolds, especially as you tackle tough weeds like marestail and giant ragweed. 
The spring pass becomes more of an added residual pass than a burndown pass. With the glyphosate resistance we now have with marestail and giant ragweed, it’s becoming a three-pass system in many cases. We need a fall burndown, an added spring residual trip and, finally, our in-crop, postemergence application. In summary, do not skip your spring burndown trip.
Stein: If your fields are clean at planting time, there will be nothing to burn down, so you can skip the burndown products, but don’t skip the trip. It is imperative that you make a herbicide application at this time, but instead of a burndown product, you want to apply a residual product — preferably with multiple modes of action. [The products you use] should control both marestail and giant ragweed, and keep them from germinating. There are several chemistries that fit this scenario well.
Summing up: You made a smart move by making a fall application and now having clean fields going into spring, especially since marestail and giant ragweed are two of your worst weeds. However, don’t let clean fields right now lull you to sleep. The CCAs suggest that if you truly don’t have any weeds, especially marestail and giant ragweed, in the field when you’re ready to make your spring preplant pass, you may not need to add burndown herbicides. However, it’s critical to still make the spring spray application so you can apply residual herbicides that will prevent many weeds from ever germinating.