2,4-D resistant waterhemp found in Nebraska
Multiple Resistance Herbicide Populations
Of particular concern are waterhemp populations where individual plants are resistant to three or more herbicide mechanisms-of-action. In these instances, growers have fewer, effective weed management options. When populations with multiple-herbicide resistance are then managed with the one or two remaining herbicide mechanisms-of-action that are still effective, the likelihood of the population evolving resistance to those herbicides is high. The herbicide use pattern in the field where the resistant population was collected included an annual burndown application of atrazine, metolachlor, and 2,4-D followed by a postemergence application of 2,4-D. Research is underway at UNL to determine whether this waterhemp population has developed resistance to additional herbicide mechanisms-of-action.
Reducing the Spread of Herbicide Resistance
New technologies that confer resistance to 2,4-D and dicamba (both synthetic auxins) are being developed to provide additional herbicide options for postemergence weed control in soybean and cotton. The development of 2,4-D resistant waterhemp in this field is a reminder and a caution that these new technologies, if used as the primary tool to manage weeds already resistant to other herbicides such as glyphosate, atrazine or ALS-inhibitors, will eventually result in new herbicide resistant populations evolving. This will limit the value of those technologies to farmers.
To minimize the risk of developing herbicide resistant weeds:
- rotate effective herbicide mechanisms of action,
- tank-mix multiple effective herbicides, and
- use effective doses.
Where possible, use an integrated weed management plan that also includes non-chemical weed control options such as crop rotation and tillage. Carefully monitor fields for changes in susceptibility to the herbicides being used and contact a UNL extension office when resistance is suspected. If multiple plants survive in a field, and that species is known to have developed resistance elsewhere to herbicides used in that field, it may be prudent to remove the survivors before they produce seed.