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Indaziflam: a new cellulose biosynthesis inhibiting herbicide provides long-term control of invasive winter annual grasses




Sebastian, Derek James, author
Nissen, Scott, advisor
Beck, George, committee member
Meiman, Paul, committee member
Gaines, Todd, committee member

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Invasive winter annual grasses such as downy brome (Bromus tectorum L.) are a threat to native ecosystems throughout the US. These invasive grasses exploit moisture and nutrients throughout the fall and early spring before native plants break dormancy. This results in decreased native species abundance and development of monotypic stands. Short-term downy brome management has been shown to be effective; however, the soil seed reserve has often been overlooked although it's the mechanism responsible for rapid re-establishment. While glyphosate, imazapic, and rimsulfuron are herbicides commonly recommended to control invasive, annual grasses, their performance is inconsistent, and they can injure desirable perennial grasses. Indaziflam is a recently registered cellulose-biosynthesis inhibiting herbicide, providing broad spectrum control of annual grass and broadleaf weeds. Indaziflam (Esplanade®, Bayer CropScience) is a cellulose biosynthesis inhibiting (CBI) herbicide that is a unique mode of action for resistance management and has broad spectrum activity at low application rates. At three sites, glyphosate and rimsulfuron provided less downy brome control than indaziflam one year after treatment (YAT). Percent downy brome control with imazapic decreased significantly 2 YAT (45-64%), and 3 YAT (10-32%). Across all sites and application timings, indaziflam provided the greatest downy brome control 2 YAT (89-100%) and 3 YAT (83-100%). At two additional sites evaluating five application timings, indaziflam treatments resulted in superior invasive winter annual grass control 2 YAT (84% ± 5.1 to 99% ± 0.5) compared to imazapic (36% ± 1.2). Indaziflam treatments significantly increased biomass and species richness of co-occurring species, 2 YAT. In a greenhouse bioassay, indaziflam was significantly more active on downy brome, feral rye (Secale cereale L.), jointed goatgrass (Aegilops cylindrica L.), Japanese brome (Bromus japonicus Thunb.), medusahead (Taeniatherum caput-medusae [L.] Nevski), and ventenata (Ventenata dubia (Leers) Coss) compared to imazapic, with the exception of jointed goatgrass. Comparing all species, the GR50 values for imazapic were on average 12 times higher than indaziflam. Indaziflam's increased activity on monocots could provide a new alternative management strategy for long-term control of multiple invasive winter annual grasses that invade >23 million ha of US rangeland. Indaziflam could potentially be used to eliminate the soil seed bank of these invasive grasses (< 5 years), decrease fine fuel accumulation, and ultimately increase the competitiveness of perennial co-occurring species.


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