A new paradigm in rangeland restoration: using a pre-emergent herbicide to assist in native plant establishment and release

Clark, Shannon Lee, author
Nissen, Scott, advisor
Dayan, Franck, committee member
Meiman, Paul, committee member
Bjostad, Lou, committee member
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Invasive winter annual grasses (IWAG), especially downy brome (Bromus tectorum L.), are a significant threat to rangeland ecosystems in the western United States. Invasions in natural ecosystems can cause severe negative impacts by reducing native plant diversity and lowering community productivity, increasing fire frequency, and displacing native vegetation that is critical wildlife and pollinator habitat. Herbicides currently used for IWAG management can provide adequate short-term control; however, results can be inconsistent and injury to desirable species can occur. Indaziflam (Esplanade®, Bayer CropScience) is a new herbicide option for long-term IWAG control in natural areas and rangeland. As a cellulose biosynthesis inhibitor, indaziflam stops root growth in newly germinated seedlings by preventing cellulose formation. Field studies were conducted to assess native plant tolerance, revegetation and broadleaf weed seedling control with indaziflam applications. At two sites, indaziflam did not impact perennial grass cover, native species richness, or the community composition of forbs and shrubs at one and two years after treatment (YAT). However, the abundance of native forbs and shrubs was reduced by treatments containing picloram and aminocyclopyrachlor. In a separate field study at two sites, a glyphosate dose response showed approximately three times more glyphosate was needed for a 50% reduction (GR50) in feral rye biomass (GR50 = 126.0 g ae ha-1) compared to downy brome biomass (GR50 = 40.4 g ae ha-1). Indaziflam treatments still resulted in reduced downy brome and feral rye biomass compared to the non-treated check 3 YAT, while imazapic and glyphosate did not provide control beyond the first year. Establishment of cool-season grasses (C3), warm-season grasses (C4) and forb/shrubs through drill seeding was only successful across all three functional groups in treatments which included indaziflam. C3 grasses had greater establishment, with an average frequency of 61 ± 1.7% (mean ± SE) at Site 1 and 46 ± 2.6% SE at Site 2 at 3 YAT. In a third field study, treatments containing indaziflam had increased Dalmatian toadflax [Linaria dalmatica (L.) P. Mill], diffuse knapweed (Centaurea diffusa Lam.), and common mullein (Verbascum thapsus L.) control 2 YAT compared to treatments without indaziflam. A laboratory assay was conducted to evaluate the impact of litter on imazapic, rimsulfuron, and indaziflam availability. Downy brome litter at 2,600 kg ha-1 intercepted 84.3 ± 1.0% SE of the applied herbicide. Simulated rainfall at 0 days (d) after application was able to recover 100% of the intercepted rimsulfuron and imazapic, while recovery decreased to 65 ± 1.7% at 1 d and 7 d. Only 54 ± 1.9% of indaziflam could be recovered at 0 d, and recovery decreased to 33 ± 1.1% when simulated rain was applied at 1d or 7 d after application. The multi-year winter annual grass control provided by indaziflam could provide a new strategy for rangeland restoration, allowing enough time for the release of the remnant native plant community or the establishment of native species through revegetation. Indaziflam could potentially be incorporated into management systems to manage the weed seed bank and extend biennial and perennial weed control.
2019 Spring.
Includes bibliographical references.
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invasive winter annual grasses
downy brome
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