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Save Yield, Kill Weeds

Keeping weeds under control is a year-round job. 

Although you might have already laid your foundation of pre-emergence herbicides, your yield isn’t safe. The next tool you need is a well-timed post-emergence herbicide application. 

“Timing is everything when it comes to weed control,” says Jason Bond, Ph.D., Mississippi State University weed scientist. 

Time Your Application
Bond recommends a post-emergence herbicide application seven to 21 days after planting. He admits that’s a large range, but it’s necessary because several elements affect good weed control:

  • Did the pre-emergence application receive rain for incorporation?
  • How large are the weeds?
  • Is the timing right for an application?

“Ideally, it would be three or even four weeks after planting before a post-emergence application, but sometimes you don’t have that option in order to stop the weeds,” says Bond. “You want to target the weeds at less than 4 inches tall. After that, it starts getting out of control.”

Know Your Technology
Bond tells farmers to think about several factors when selecting the herbicides to go into their post-emergence tank mix, but technology is the first one.

“Whether it’s Roundup Ready or Liberty Link, or whatever there will be in the future, you need to be aware of which technology is in the field in order to select the right herbicides,” he says.

Acquire Your Target
The next step in establishing control is to identify your target – your biggest weed problem.

“Once you have the right herbicide to address your primary weed problem, which is more than likely Palmer amaranth, then you need to think about what to add in the mix to control your second-biggest weed threat,” says Bond.

He says you should also make sure you have the correct components – like a surfactant, if needed –in your tank mix to get the best weed control.

Calibrate Your Equipment
Small details can make or break your herbicide application. Bond says to pay attention to water volume and nozzle selection.

“Some herbicides are especially sensitive to water volume; with others, nozzle selection matters,” he says. “Water volume, combined with nozzle selection, determines the size of the droplet when it hits its target.”

Once your sprayer is calibrated, then you have to think about the wind and the consequences of drift, including the possibility of not hitting your target or affecting sensitive plants growing downwind.

After checking off all these boxes for post-emergence application, Bond says you should always remember one thing: “Don’t go across the field spraying without a mixture of herbicides that includes both post-emergence and residual activity on your target weeds,” he says.

For more weed management tips, visit our weed’s resources page