Post Residual Herbicides

In broad terms, post-residue means an herbicide that can be applied post-emergence to a crop that has soil residual weed activity. There are a number of herbicides that can be applied safely to emerged crops offering soil residual weed activity but most have little or no activity to emerged weeds.

To take care of the emerged weeds, these products are tank-mixed with another herbicide such as Liberty^® herbicide, glyphosate, or 2,4-D, which have post-activity on weeds but little or no soil residual activity. Several group 15 herbicides, such as Outlook^® herbicide or Zidua^® SC herbicide, fit the post-residual category for both corn and soybeans, adding a residual component for several weeks of protection from germinating weeds.

Overlapping residual protection from planting to crop row closure is essential to avoid yield-robbing interference from weeds and to reduce weed seed production in your field. An effective approach is to follow a planting time soil residual herbicide with a post-residual application.

📸: BASF Contributing Writer/Featuring a field as a side by side comparison of an effective post residual weed control strategy.

Watch labeled crop stage timing

All post-residue herbicides have labeled crop growth stages based on crop safety and herbicide residue limits. For example, Outlook^®  herbicide can be applied over the top of corn up to 12” tall (36" for layby). In soybeans, it can be applied over the top of soybeans up to the V5 stage. Zidua^® SC herbicide can be applied over the top of corn through the V8 stage, while in soybeans it can be applied up to V6 soybeans. New Surtain™ herbicide can be applied up to V3 corn and offers three modes of action for superior control of problem weeds. 

For best results, most applications should be made well prior to those maximum stages. 

Earlier applications of a post-residual will also allow for a better chance to catch a rain in early summer, ensuring herbicide activation and satisfactory results.

Watch labeled weed height

Post residuals do need to be applied at a time when the post-active herbicide in the mix is most effective, as applying to small emerged weeds will almost always give better results than waiting until the maximum labeled weed height. Also, applying to smaller weeds may mean you may be able to use a lower rate of the post-active herbicide.

Pick effective tank mix partners

Both your post-active herbicide and soil residual herbicide need to complement each other by filling holes in the weed spectrum. Also, make sure you are using multiple modes of action on problem weeds, such as waterhemp and palmer amaranth, for complete control and resistance management. 

Consider using different modes of action on the same weed with your planting time and post residual applications. A good one-two soil residual punch on waterhemp or palmer amaranth is to use a group 14 herbicide such as Sharpen^® herbicide or Verdict™ herbicide at planting, followed by a group 15 herbicide such Outlook^® herbicide or Zidua^® SC herbicide at the post-residue timing.

📸: @Photodjo via Canva/Featuring a grower standing in a clean soybean field.

Choosing an effective soil residual herbicide, whether at planting time or at the post-residual timing, will allow control of those that do escape to be better controlled by the post-active herbicide, especially if your post-application is delayed due to weather.

Always read and follow label directions. Grow Smart, Liberty, Zidua, Sharpen, and Outlook are registered trademarks of BASF. Verdict is a trademark of BASF. Copyright 2024 BASF Corporation. All rights reserved.

This content is being brought to you in partnership with Grow Smart^® Live and contributing guest authors. BASF provides the information in this article as a service to its customers; however, the views expressed by guest writers are their own and do not necessarily reflect the views of BASF.