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Weed-Suppressive Bacteria Have No Effect on Exotic or Native Plants in Sagebrush-Steppe

Germino, Matthew J., Lazarus, Brynne E.
Rangeland ecology & management 2019
Artemisia, Bromus tectorum, Pseudomonas fluorescens, Taeniatherum caput-medusae, adverse effects, annuals, climate, discing, ecoregions, experimental design, grasses, imazapic, indigenous species, introduced plants, mixing, nontarget organisms, rangelands, rimsulfuron, soil, soil bacteria, steppes
Approaches and techniques for control of exotic annual grasses are a high priority in rangelands including sagebrush steppe. Strains of the soil bacterium Pseudomonas fluorescens have been proposed to be selectively pathogenic to multiple species of exotic annual grasses (“Pf,” weed-suppressing bacteria, “WSB”). However, defensible tests of the target and nontarget effects of these WSB strains in the field are needed. We evaluated the effects of D7 and MB906 strains of Pf WSB in sagebrush steppe invaded by cheatgrass (Bromus tectorum L), medusahead (Taeniatherum caput-medusae L. Nevski), and other exotic annual grasses. We evaluated the WSB strains with and without herbicides (imazapic, rimsulfuron) or discing to mix surface-spray of the WSB into deeper soils, and we replicated these tests in three ecoregions that differed in soils and climate. Over 3 yr after treatment, neither WSB strain affected cover of exotic annual grasses, perennial bunchgrasses, or the total community, either with WSB alone or in combination with herbicides or discing. WSB has received considerable attention and is being applied across large rangeland areas, but the WSB strains and methods applied here were ineffective. We recommend any future WSB use applied using experimental design and measurement until its effects can be proven.