Selective herbicide application is a common restoration strategy to control exotic invaders that interfere with native plant recovery after wildfire. Whether spraying with preemergent or bioherbicides releases native plants from competition with exotics (“spray-and-release” strategy) and can make communities resistant to re-invasion by exotic annual grasses (e.g., cheatgrass, medusahead), without risks to non-target native plants or secondary invasion, is a major question for land managers of semiarid plant communities. We applied chemical herbicides (imazapic, rimsulfuron) and weed-suppressive bacteria (Pseudomonas fluorescens strains MB906 and D7) to three different SW Idaho sagebrush-steppe communities after fire. We measured plant cover prior to burning and for four years after treatments.

Selective herbicide application is a common restoration strategy to control exotic invaders that interfere with native plant recovery after wildfire. Whether spraying with preemergent or bioherbicides releases native plants from competition with exotics (“spray-and-release” strategy) and can make communities resistant to re-invasion by exotic annual grasses (e.g., cheatgrass, medusahead), without risks to non-target native plants or secondary invasion, is a major question for land managers of semiarid plant communities. We applied chemical herbicides (imazapic, rimsulfuron) and weed-suppressive bacteria (Pseudomonas fluorescens strains MB906 and D7) to three different SW Idaho sagebrush-steppe communities after fire. We measured plant cover prior to burning and for four years after treatments.

The exotic grass-fire cycle is degrading semiarid rangelands, such as the vast areas of shrub-steppe in North America now invaded by fire-promoting cheatgrass. Chemical- or bio-herbicides are sprayed onto soils to inhibit the invaders, but information on chemical- or bio-herbicide effects on plant communities is limited. We asked how the plant community responded to the bioherbicide Pseudomonas fluorescens strain ACK55 (Battalion Pro®) in comparison to the separate and combined effects of the most conventional pre-emergent chemical herbicide, imazapic (Plateau®), in two cheatgrass-invaded sagebrush-steppe sites. Plant community responses are compared with soil microbial community responses in the Larger Work, and soil microbial data are available in GenBank. Plant community responses are compared with soil microbial community responses in the Larger Work, and soil microbial sequence data were deposited to the NCBI Short Read Archive (BioProject PRJNA1254875).

Top-down and bottom-up factors affecting invasive populations are rarely considered simultaneously, yet their interactive responses to disturbances and management interventions can be essential to understanding invasion patterns. We evaluated post-fire responses of the exotic perennial forb Chondrilla juncea (rush skeletonweed) and its biocontrol agents to landscape factors and a post-fire combined herbicide (imazapic) and bacteria (Pseudomonas fluorescens strain MB906) treatment that targeted invasive annual grasses in a sagebrush steppe ecosystem. Biocontrol agents released against C. juncea in previous decades included Cystiphora schmidti (gall midge), Aceria chondrillae (gall mite), and Puccinia chondrillina (rust fungus). C. juncea abundance was greater in sprayed than unsprayed plots, and where soils were coarser, slopes faced southwest, solar heat loads and topographic water accumulation were greater, and cover of deep-rooted native perennials was lower. Mite infestation was greater in unsprayed plots, midge infestation was greater at higher elevations on steeper slopes, and midges were more abundant while rust was less abundant on gravelly soils. Biocontrol infestation levels varied considerably between years and could not be predicted in 2019 from 2018 infestation levels. Multiple biocontrol species were often present at the same plots but were rarely present on the same C. juncea individuals. These results suggest that spatial patterns of invasion by C. juncea are related to deep-soil water availability, warmer conditions, and alleviation of competition. Treatments designed to reduce invasive annual grasses may inadvertently release C. juncea by both reducing plant competition for soil resources and affecting biocontrol agent (mite) abundance.

Top-down and bottom-up factors affecting invasive populations are rarely considered simultaneously, yet their interactive responses to disturbances and management interventions can be essential to understanding invasion patterns. We evaluated post-fire responses of the exotic perennial forb Chondrilla juncea (rush skeletonweed) and its biocontrol agents to landscape factors and a post-fire combined herbicide (imazapic) and bacteria (Pseudomonas fluorescens strain MB906) treatment that targeted invasive annual grasses in a sagebrush steppe ecosystem. Biocontrol agents released against C. juncea in previous decades included Cystiphora schmidti (gall midge), Aceria chondrillae (gall mite), and Puccinia chondrillina (rust fungus). C. juncea abundance was greater in sprayed than unsprayed plots, and where soils were coarser, slopes faced southwest, solar heat loads and topographic water accumulation were greater, and cover of deep-rooted native perennials was lower. Mite infestation was greater in unsprayed plots, midge infestation was greater at higher elevations on steeper slopes, and midges were more abundant while rust was less abundant on gravelly soils. Biocontrol infestation levels varied considerably between years and could not be predicted in 2019 from 2018 infestation levels. Multiple biocontrol species were often present at the same plots but were rarely present on the same C. juncea individuals. These results suggest that spatial patterns of invasion by C. juncea are related to deep-soil water availability, warmer conditions, and alleviation of competition. Treatments designed to reduce invasive annual grasses may inadvertently release C. juncea by both reducing plant competition for soil resources and affecting biocontrol agent (mite) abundance.

Proliferation of cheatgrass and other exotic annual grasses such as medusahead and ventenata are a major environmental concern and operational problem for roadsides in Idaho. These annual grasses are highly flammable and they shorten fire-return intervals. Flammable vegetation is particularly hazardous in roadsides because of proximity to a ready source of ignition, and fires that start on roadsides can spread into adjacent public lands and urban communities with sprawling home development, causing extensive and expensive damage and degradation to wildlife habitat, rangelands, private or public property, utilities, etc. Thus, the Idaho Transportation Department (ITD) has a strong interest in preventing roadside vegetation from becoming invaded by exotic annual grasses and in improving vegetation on roadsides that are currently invaded, replacing exotic annual grasses with perennial bunchgrasses and forbs that support pollinators. These data were generated in roadside tests of various tools designed to reduce exotic annual grasses on the landscape, as well as techniques designed to improve the efficacy of these tools. These include the ACK55 strain of the bacterium Pseudomonas fluorescens, which was isolated to target cheatgrass, medusahead and jointed goatgrass (aka “weed-suppressive bacteria”, hereafter “WSB”). We also tested a relatively new pre-emergent herbicide, indaziflam (Rejuvra®) thought to remain active in soil for years after application. We tested these against and in combination with the “workhorse” pre-emergent herbicide most frequently sprayed by land managers for exotic annual grass control, Imazapic (Plateau®).

Proliferation of cheatgrass and other exotic annual grasses such as medusahead and ventenata are a major environmental concern and operational problem for roadsides in Idaho. These annual grasses are highly flammable and they shorten fire-return intervals. Flammable vegetation is particularly hazardous in roadsides because of proximity to a ready source of ignition, and fires that start on roadsides can spread into adjacent public lands and urban communities with sprawling home development, causing extensive and expensive damage and degradation to wildlife habitat, rangelands, private or public property, utilities, etc. Thus, the Idaho Transportation Department (ITD) has a strong interest in preventing roadside vegetation from becoming invaded by exotic annual grasses and in improving vegetation on roadsides that are currently invaded, replacing exotic annual grasses with perennial bunchgrasses and forbs that support pollinators. These data were generated in roadside tests of various tools designed to reduce exotic annual grasses on the landscape, as well as techniques designed to improve the efficacy of these tools. These include the ACK55 strain of the bacterium Pseudomonas fluorescens, which was isolated to target cheatgrass, medusahead and jointed goatgrass (aka “weed-suppressive bacteria”, hereafter “WSB”). We also tested a relatively new pre-emergent herbicide, indaziflam (Rejuvra®) thought to remain active in soil for years after application. We tested these against and in combination with the “workhorse” pre-emergent herbicide most frequently sprayed by land managers for exotic annual grass control, Imazapic (Plateau®).

Data includes functional group cover of exotic annual grasses, deep rooted perennial grasses, and shallow rooted perennial grasses within the first five years after the 2015 Soda wildfire across different post-fire restoration treatments. Additional landscape and weather covariates hypothesized to influence treatment effectiveness are included.

We conducted a case studies testing effectiveness of a soil borne bacteria, Pseudomonas fluorescens strain D7, in controlling Bromus tectorum (cheatgrass) and in affecting the density of sown desirable seedlings. Response variables (foliar cover, aboveground biomass, and density of B. tectorum; density of sown native plants) were measured for three years after treatment.

Eighty-one monitoring plots within the Minidoka National Wildlife refuge on the Snake River Plain in south-central Idaho were surveyed in July-August from 2020 to 2023 to evaluate the effects of herbicides on the vegetation-community across areas that varied in both burn history and background cheatgrass abundance. Surveys consisted of line-point intercept measurements along two 6m or 50m transects with 100 points of observation per line. In spring of 2023 "escaped" cheatgrass individuals were counted in each 6x6m herbicide-treated plot.