Open Space Advisory Board Agenda and Packet 2019 10 09

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Research Hypothesis: We hypothesized that treatments including indaziflam would provide significantly longer annual and biennial weed control preventing re- establishment, as compared to treatment excluding indaziflam. Section 2: Anticipated Value of the Research/Contribution to Management Needs: Annual, biennial, and perennial weeds including downy brome, common mullein, diffuse knapweed, field bindweed and Russian thistle are often present on similar rangeland, roadside, and disturbed sites along the Front Range of Colorado. These species are found on City of Louisville Open Space properties including Aquarius and Davidson Mesa Open Space. These highly invasive species compete with desirable native species for early spring moisture and have the capability to spread from disturbed to undisturbed areas. Downy brome also germinates in the fall and early spring, exploiting moisture and nutrients before native plant communities begin active growth in the spring. Downy brome seeds are tolerant to temperature and moisture stress and can remain viable in the soil for up to 5 years. Land managers have been faced with the problem of selectively controlling biennial invasive species with broadleaf herbicides. For invasive winter annual grasses such as downy brome, chemical control options include imazapic, rimsulfuron, and glyphosate; however, these herbicides lack consistency beyond the initial year of application and have been shown to injure desirable plant communities. Indaziflam (EsplanadeTM, Bayer CropScience) is a relatively new herbicide that is currently registered for annual weed control in turf, orchards, and noncropland. Indaziflam is used at rates between 3.5 and 7 oz/A and has excellent preemergence activity on many annual weed species (Fig. Al). Indaziflam has several attributes that make it an ideal candidate to control non -crop weeds that reproduce primarily by seed production, 1) long soil -residual activity and 2) no injury to perennial grasses, forbs, and shrubs (Figs. A2-9). This combination would increase the opportunity for successful restoration of City of Louisville Open Space properties. Because indaziflam is a root inhibiting herbicide this allows for increased safety on desirable perennial plants, that have roots below the layer where the herbicide is active (Fig. Al). The emerged plants at the time of application would be initially controlled by the tank mix partner (picloram, aminocyclopyrachlor, etc.), while indaziflam would provide the long-term control of subsequent seedlings. Field studies at CSU have demonstrated that indaziflam has excellent long term downy brome control (3+ years) with minimal injury to native perennial species (Figs. A2-6). A greenhouse study has shown indaziflam can control downy brome, diffuse knapweed, common mullein, and several other biennial seedlings at rates as low as 1 oz/A. Several research trials were conducted on the City of Louisville Open Space properties to ultimately provide additional management options for long-term control of invasive annual and biennial weeds where treatments in the past have provided inconsistent, short-term control. Fewer herbicide applications would mean additional years for native species to respond and recover, a lighter load of herbicides sprayed on managed properties, and the financial/labor savings from yearly herbicide treatments or mowing operations. This research provides an insight into the long-term control of invasive weed species and the effect of herbicide treatments on desirable grass and forb species. Section 3: Methodology 12