How to Apply Herbicides in a Drought

corn emerging in drought

When you’re under drought stress, spray your corn herbicides sooner rather than later.

  • Herbicides perform best when there is ample soil moisture and weeds are thriving.
  • If your region is headed toward a drought, spray when weeds are small to maximize herbicide performance.
  • Apply full, labeled rates to help improve weed control and resistance management.

Every year, drought impacts growers throughout in the U.S., and hot, dry conditions can make controlling weeds tougher than usual.

“Herbicides work very well when weeds have ‘wet feet,’ as I call it – soil moisture.”

Mike Weber
Principal Scientist, Bayer

“Herbicides work very well when weeds have ‘wet feet,’ as I call it – soil moisture,” said Bayer Principal Scientist Mike Weber.

If you’ve gone two weeks or more without rain, heed Weber’s top three tips for improving the effectiveness of your herbicide sprays:

  1. Always apply full-labeled rates of your chosen herbicides. “Cutting rates is a big mistake,” Weber says, “given the growing prevalence of weed resistance.” This is especially true in hot, dry conditions, when weeds become more tolerant to herbicides.
  2. Consider adding an adjuvant to your tank. Crop oil concentrates and non-iconic surfactants can help to aid in absorption issues, allowing the chemical to penetrate the weed’s waxy cuticle, which can thicken in a drought.
  3. Spray weeds when they are less than 3 inches tall. If you’re going after driver weeds like waterhemp or common lamsbquarter, smaller is always better, but particularly in a drought. “If those weeds are 8-10 inches tall, the herbicide is going to be inconsistent,” Weber says. “Consistency increases exponentially in abnormal growing conditions when you target small weeds.”

Identifying droughty conditions

Droughty conditions are different across the U.S. What a grower in Iowa would call a drought is very different from what a grower in Colorado or Arkansas might consider dry. It can also differ across fields: Crops growing in sandy soil will experience drought stress sooner than those growing in heavy soil.

So, how do you know when to adjust your herbicide application plans? 

“In general, if you don’t have any type of moisture within a two-week period – depending on what fell from the sky the previous two weeks – in general we would call that a dry trend,” Weber says.

How drought impacts weed control

Weeds growing under these droughty conditions often become more tolerant to herbicides. “Besides developing a thicker-than-normal cuticle – a waxy barrier to chemical absorption – drought also slows herbicide translocation within a weed”, Weber says. Consequently, application of herbicides under such conditions often results in reduced weed control.

“In a drought scenario, you want to make sure you pull the trigger earlier and spray smaller weeds, so you’re maximizing the performance of your herbicide,” Weber says.

Not only can spraying earlier in the season improve outcomes, but spraying earlier in the day can, too. Translocation and water uptake in weeds occur in the morning; weeds take in herbicides rapidly and translocate them to all areas of the plant. Later in the day when the sun is hot, stomates close to conserve water.

Reactivation provides added protection from weeds

When dry weather sets in, most herbicides lose residual weed control, and new weeds emerge. That can lead to increased expenses from extra sprays. Using a pre-emergence herbicide with reactivation properties, like Corvus® herbicide, helps growers maintain lasting residual weed control – even if weather conditions turn dry.

With a half-inch of rain, the active ingredient reactivates itself to control weeds that may have emerged, and also prevent new weed growth.

Safeners can lessen crop stress

Safeners are designed to help crops metabolize herbicides. For a corn plant under drought stress, this means it can recover more quickly than when sprayed with another herbicide without a safener. Corvus and DiFlexx® DUO herbicides from Bayer feature built-in safeners.

“With a drought stress scenario, we do have safeners that really help the crop metabolize the herbicide,” Weber says. “That's been one of our calling cards with Bayer and our herbicide portfolio for several years now.”

Using Corvus and DiFlexx DUO corn herbicides

With over 10 years of proven performance, Corvus (2,27) is the No. 1 pre-emergence corn herbicide.* Growers turn to Corvus to get an early win against weeds for end of season rewards.

  • Application rate: 3.3 to 5.6 fl oz/A
  • Timing: Burndown, pre-plant, pre-plant incorporated, pre-emergence and post-emergence through V2
  • Recommended tankmix options: Atrazine (5), Roundup® Brand Agricultural Herbicide (9), Harness® (15), Dual® (15)

DiFlexx DUO (4,27) takes down tough weeds, like waterhemp and Palmer amaranth, with two powerful and effective sites of action.

  • Application rate: 24 to 40 fl oz/A
  • Timing: Corn up to 36 inches or up to V7 growth stage for broadcast application/up to V10 for directed application
  • Recommended tankmix options: Atrazine (5) for corn under 12 inches tall, Roundup Brand Agricultural Herbicide (9)

To learn more, contact a Bayer representative.

*Amongst growers – Source: Brand Health Check


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©2019 Bayer Group. Always follow grain marketing and all other stewardship practices and pesticide label instructions. Bayer, the Bayer Cross, Corvus, DiFlexx, and Roundup are registered trademarks of Bayer Group. Roundup Ready® 2 Technology contains genes that confer tolerance to glyphosate. Glyphosate will kill crops that are not tolerant to glyphosate. Corvus is a Restricted Use Pesticide. Not all products are registered in all states and may be subject to use restrictions. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. For additional product information, please call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.CropScience.Bayer.us. Bayer CropScience LP, 800 North Lindbergh Boulevard, St. Louis, MO 63167. [Insert CR code here]

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