In chickweed collected from one particular field in New Kent County, Hagood recalls 32 times the labeled rate of Harmony had no visible effect. Of more concern, he says, samples from this field were sprayed with a number of other sulfonylurea herbicides, with a similar lack of control.

“We also tested these resistant plants to other ALS herbicides other than the sulfonylurea herbicides. The New Kent site was resistant to both Pursuit and Arsenal.

“Arsenal, in particular, is a very persistent and effective herbicide and resistance to this material should give growers some insights as to how difficult multiple herbicide resistant chickweed will be to manage,” Hagood says.

Since Hagood’s initial discovery, resistance problems have become an ever-increasing problem and continue to be a significant threat to the big wheat crop planted in the Upper Southeast last fall.

North Carolina State University Small Grains Specialist Randy Weisz says a good option for growers this spring to ALS-inhibiting herbicides, like Harmony Extra, Osprey, Powerflex and Finesse; may be to use 2,4-D or dicamba either alone, or in a tank-mix one of these ALS-inhibitors.

He points out that dicamba may be a better choice if henbit and chickweed are the major weed problems.

The North Carolina State specialist says that growers using either 2,4-D or dicamba should remember that both of these herbicides should only be applied after tillering is complete and before wheat plants begin jointing.

In future years Weisz suggests rotating or mixing chemistries.

An example of rotation across seasons might include using a pre-emergence or spike stage herbicide (like Axiom, or Valor) one year, Harmony Extra, Osprey, or PowerFlex the next year, and 2,4-D or dicamba in the third year.

Chemistries can also be mixed within a season by using a pre-emergence or spike stage herbicide followed by Harmony Extra, Osprey, or PowerFlex a few months later.

An easy approach to preventing resistance might also be to just tank-mix two herbicides with different modes of action such as Harmony Extra and dicamba.

He says that a rotation of using Axiom or Valor one year followed by one of the ALS herbicides the following year should also be good for preventing ryegrass resistance.


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“There are many ways growers can implement a resistance management program. The examples above are only examples, not absolute recommendations. Harmony Extra is still an excellent broadleaf weed control option in North Carolina and Osprey and Powerflex will provide control of small broadleaf weeds and grasses,” Weisz says.