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Project description

Controlling establishing infestations of herbaceous perennials in the Lake Tahoe Basin. (03XN014)
Program Exotic Pests and Diseases Research Program
M. Renz, Extension Plant Sciences, New Mexico State University
W.E. Frost, UCCE El Dorado County
Host/habitat Wildland
Pest Perennial Pepperweed Lepidium latifolium; Dalmation Toadflax Linaria dalmatica; Yellow Toadflax Linaria vulgaris; Russian Knapweed Acroptilon repens; Spotted Knapweed Centaurea maculosa
Discipline Weed Science
Natural Systems
Start year (duration)  2003 (Three Years)
Objectives The overall goal of this project is to quantify the effectiveness of a cut-blade herbicide delivery method, which minimizes the use of herbicides while maximizing control of establishing herbaceous perennial weeds.

Quantify the effectiveness of timing of application and herbicide rate of approved herbicides applied to the lower surface of stems that are cut from four herbaceous perennial weed species (perennial pepperweed, yellow or dalmation toadflax, spotted knapweed, Russian knapweed) in the greenhouse.

Compare the effectiveness of the top three treatments for each species found within objective 1 and a conventional spot spray application at two different sites within the lake Tahoe Basin.

Evaluate the response of resident vegetation to the various applications in objective 2 over a two-year period.

Several herbaceous perennial weed species have recently established within the Tahoe Basin. While control methods exist for these species, they cannot be implemented in sensitive areas within the Tahoe Basin. A new herbicide delivery method that deposits herbicide on the lower side of a cut surface of plants may provide effective control of these herbaceous perennials. This method minimizes herbicide inputs into the environment while applying the herbicide solution to target species exclusively. By quantifying the effectiveness of this new method, we hope to provide land managers with an effective management option for the eradication of establishing infestations of herbaceous perennial weeds within the Tahoe Basin.
Two field sites each were located within and/or around the Lake Tahoe Basin for Dalmatian toadflax, perennial pepperweed, and diffuse knapweed. Vegetation data as percent cover of each species were collected in 4m2 plots, plots were treated with one of four or five treatments after data collection during year one, and percent cover and density data were collected again in year two. Results showed a significant decrease in cover for Dalmatian toadflax using the dip and clip method with telar (p < 0.05) and glyphosate (p < 0.05) when compared to untreated controls. Percent cover of diffuse knapweed decreased significantly compared to control when using transline with both the dip and clip method (p < 0.05) and the spot spray method (p < 0.05). Due to its close proximity to streams and the heavy snowfall in winter 2004 and 2005, the perennial pepperweed sites had a large amount of variability. While we did not see reductions in perennial pepperweed cover compared to the untreated controls, we did see significant decreases in the glyphosate (p < 0.05) and telar (p < 0.05) dip and clip plots post treatment compared to pre-treatment.

The greenhouse experiment indicated that the dip clip treatment significantly decreased perennial pepperweed, regardless of herbicide used. Both glyphosate and chlorsulfuron (telar) decreased living belowground biomass and increased dead belowground biomass of perennial pepperweed (p < 0.05), though it did not effect new root production or belowground stem production. Smaller original root fragments had significantly more root death than larger root fragments (P < 0.001) indicating the treatment has greater efficacy on younger plants than older plants. A second set of treatments may more effectively kill older and larger perennial pepperweed plants.

This project has just been initiated for the spring/summer field season of 2004. Funds have just been received and the greenhouse portion of the experiment will be treated between March 29, 2004 through April 2, 2004, Greenhouse results will be taken 30 days after application and be available to help guide field applications that will occur between June 1, 2004, and July 1, 2004. A part-time post doc (Jennifer Erskine, PhD) has also been hired to coordinate the field experiments in the Lake Tahoe basin. Currently she is finding appropriate sites with infestations of herbaceous perennials (perennial pepperweed, dalmation toadflax, yellow toadflax, Russian knapweed, and spotted knapweed) to conduct the field trials within or near the Lake Tahoe basin. While initial results will be collected this season, conclusive control information and impact on resident vegetation will not be available until the summer of 2005.

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