How much herbicide is left in the April planted corn?

Author: Larry Steckel, Extension Weed Specialist 2 Comments

Judging by rating corn trials this week the answer depends upon the herbicide.  Atrazine or dicamba used pre plant started breaking last week about 14 days after application.  Many of the other common pre applied herbicides like Lexar, Corvus or Bicep were still holding. 

The treatments in our studies have seen 12” of rain since they were applied.  Some of the pre applied herbicides in corn across the state have experienced even more than that.  With that kind of rainfall, do not expect any pre applied herbicide to last like it did last year.  As we saw last spring, under dry conditions a pre applied herbicide can provide weed control for 5 weeks or more.  This year with the amount of rainfall Tennessee has experienced expect pre applied tankmixtures to start to play out about 3 weeks after application. 

With the warm and wet environment in the forecast for this weekend, I would expect to see weeds start to break through.  If they do, I would manage these corn fields as if no herbicide has been applied. What I mean by that is plan to re-apply a herbicide that can provide some residual control.  There are a number of good herbicide options that can be applied post in corn.  These include atrazine, Status, and the popular premixes Halex GT, Capreno and Realm Q, just to name a few.  A more thorough discussion of these corn post options was posted on an April 11 blog and can be found here: (Corn Pre Applied Herbicide Considerations). 

Where this gets complex is the season use limits on these products. An example would be that, by the label, a field can have 2.5 qts/A of atrazine applied if split between two applications. So a field will in reality have 1.5 qts/A of atrazine on it when 2 qts/A of Bicep was applied pre emerge.  So another 1 qt of atrazine can be applied post in the next week to 10 days if a new flush of weeds appears.  Please be mindful that atrazine can be applied post only up to 12” tall corn.   All the other herbicides mentioned above have season use limits as well. 


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2 thoughts on “How much herbicide is left in the April planted corn?

  1. I know we talked about this briefly the other day, but would you discuss again how much herbicide is left on cotton and soybean ground (Valor, Fierce, Clarity etc) from burndown, much of which was sprayed 30+ days ago and has had 10+ inches of rain. How should these fields be managed from now till planting? Also, with 70% chance of rain predicted for Friday and cooler temps over the weekend forecasted, would you advise planting cotton (treated) on upland, well drained soil this week or wait till next week? Thanks.

    1. Shane

      Thanks for the comment. We have quite a few herbicides out in the time frame you asked about. Clarity is long gone. Fierce is still holding on well. Valor is playing out. LeadOff is begenning to play out as well. As far as what to do with them until planting….. I would let them go and concentrate on planting what you can. Then when you run the planter in these fields and weeds are present apply Gramoxone with the Pre.

      As far as whether to plant or not? I would be inclined to start planting those hills if the soil is not heavy. Yes there is a 60% chance for Dyersburg Friday and Sun to Wed of next week look dry but then there is a 50% chance of rain next Thursday. So whether you start this week or next week the forecast looks similar. The only difference is historically we are in the prime time to plant cotton this week.

      Thanks again,

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