Invasive weeds create an array of challenges for land managers.  The method currently used to obstruct unwanted growth is hand pulling, a technique that is only moderately effective after years of repetition.  Soil disturbances and erosion are unwanted side effects of pulling weeds manually, and can compound issues like compromised clarity of surrounding water.

Now, Cooperative Extension associates from three western states have developed an improved technique for battling noxious weeds.  Susan Donaldson, University of Nevada, Reno; Jennifer Erskine-Ogden, University of California, Davis; and Mark Renz, University of Wisconsin-Madison, have issued their findings in A Precision Method for the Control of Perennial Herbaceous Species in Sensitive Locations (http://www.unce.unr.edu/publications/SP06/SP0609.pdf).

The method offers land managers an alternative for controlling small infestations in sensitive locations and diverse plant communities. The dip-and-clip procedure allows carefully targeted herbicide application that decreases the risk of environmental contamination.  It is a variation of a procedure in which plants are cut and herbicide is applied to the remaining stump. The new treatment proved successful in decreasing invasive weed re-growth in tests conducted at Lake Tahoe, an environmental area known for its ecological sensitivity.

"The Lake Tahoe Basin Weed Coordinating Group had identified several locations in which no other method was available to control these invasive weeds," said Donaldson.  "Without this method, we were concerned that infestations would continue to spread and threaten lake clarity."

The technique involves dipping clipper blades into an herbicide solution so that with each cut of a plant stem, excess solution is deposited in the remaining stem.  Immediate application of herbicide ensures translocation into the roots, essential for plant death.  The technique avoids issues related to spray drift that could occur using traditional herbicide application methodology, and decreases the risk of water contamination.

While the dip-and-clip method is moderately expensive and labor intensive for the first year of treatment, Cooperative Extension research shows that second-year infestations in treated areas do decrease.  This in turn allows native herbaceous and woody plants to reestablish and continue healthy growth, according to Erskine-Odgen.

"Invasive weeds threaten environmental thresholds at Lake Tahoe, which validates the need for this improvement in methodology for controlling noxious weeds," said Donaldson.

Three perennial invasive weeds found in the Lake Tahoe area – perennial pepperweed, Dalmatian toadflax and diffuse knapweed – require herbicidal treatment for effective control.  These aggressive species tolerate a variety of conditions that damage some plants such as drought, grazing, burning and mowing; however, the dip-and-clip method has proven successful in lowering their annual re-growth.