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Cool weather may challenge weed control in wheat

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Column by Hardin County Extension Service Agent Matt Adams

As we progress through thiscooler-than-normal spring, wheat growers quickly are being faced with weed management decisions.

This spring, the million-dollar question has been, “Will my herbicides work in these cool temperatures?” Some growers have delayed herbicide applications in hope of better weather in coming days.

Stress conditions, whether they be moisture or temperature related, limit physiological processes in all plants, including weeds, to some degree.  This can limit the response of weeds to herbicide applications.  Adequate levels of control often can be achieved, but the slower activity of the herbicide application sometimes allows weeds to recover before a crop can out-compete them.

The slower activity of the plants caused by cooler temperatures also may slow the metabolic process of the herbicide by the desired crop, resulting in crop injury. 

So, back to the original question — do you spray or wait for better weather? The number and size of the weeds, as well as weed species in the spectrum ultimately determine the answer.  If you feel you can wait a few days and still maintain adequate weed control, the logical choice is to wait.

Dr. Jim Martin, University of Kentucky Extension weed specialist, recently gave the following tips to consider as we progress through the next few days:

  • Harmony and Harmony Extra are examples of ALS-inhibitor herbicides that can injure wheat in cool wet soil conditions. Injury also may occur if wide fluctuations of day and nighttime temperatures occur prior to, or soon after, application. It is not clear to what extent, if any, the injury observed for Harmony and Harmony Extra impacts wheat yield. The labels of these products recommend adding 2,4-D  as a tank mix partner to limit the risk of injuring wheat from the ALS-inhibitor herbicides. It is important to recognize the safest time to use 2,4-D in wheat is when plants are fully tillered and prior to jointing. 
  • Some growers may be tempted to include Clarity, Banvel or other products that contain dicamba as a tankmix partner with other herbicides to enhance control of certain broadleaf weeds. To limit the risk of injuring wheat, avoid using dicamba once wheat begins to joint.
  • When controlling wild garlic with Harmony, Harmony Extra or similar generic products, allow time for plants to develop 2 to 4 inches of actively growing tissue. The new growth emerges from the base of the plants and not from the old leaves that have tip burn from cold temperatures.

For more information about weed control in wheat, contact the Hardin County Extension Service at (270) 765-4121.

Matt Adams is a Hardin County Extension Service agent for agriculture and natural resources.