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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Research Project #442706

Research Project: Development of Cheatgrass Biological Control with Microbes and Integrated Cape-ivy Control to Reduce Populations of Non-native, Invasive Weeds

Location: Invasive Species and Pollinator Health

Project Number: 2030-22000-033-013-I
Project Type: Interagency Reimbursable Agreement

Start Date: Aug 1, 2022
End Date: Sep 30, 2025

Invasive exotic weeds occupy tens of millions of hectares of rangeland, forest, wetland and associated riparian ecosystems. Weeds threaten biodiversity and reduce availability and quality of water and soil resources, costing over $7B per year. In the western US, cheatgrass (Bromus tectorum) is the most widespread invasive grass species. Cheatgrass has a host of negative effects on ecosystems: it is a low-quality forage for livestock and wildlife, shortens established fire regimes and increases fire risks, decreases carbon storage in soils and biomass and negatively affects biodiversity. Along the coast, a vining perennial plant known as Cape-ivy (Delairea odorata) has invaded sensitive riparian, forest and scrubland habitats, consuming water and smothering vegetation, and costing the CA Department of Parks and Recreation over $100K per year and thousands of staff and volunteer hours to control by hand. Dense dead mats of Cape-ivy draped over trees may exacerbate fire hazards in coastal forests and shrublands. Control of cheatgrass and Cape-ivy with chemical herbicides is not a feasible option for ecosystem-wide management. Biological control is the only sustainable long-term control option. For cheatgrass, weed-suppressive bacteria offer a promising alternative for large-scale and long-term control; however, currently available strains, such as Pseudomonas fluorescens strains (e.g., ACK55) have shown uneven results in field trials, with highly successful treatment in some locations but not others. This inconsistent response could be due to interactions between ACK55 and the resident soil microbial community (microbiome). Here, we will integrate spatial and temporal sampling of cheatgrass-invaded rangelands in the UC Reserve System and possibly other SPF sites to determine changes in the taxonomic and functional composition of the soil microbiome across different soil types and time scales using molecular methods. Characterization of the microbiome will likely lead to discovery of known or novel bacteria or fungi that are commonly associated with cheatgrass, and that might facilitate its invasion. In the case of Cape-ivy, a shoot tip-galling fly has been released by USDA-ARS and is established at at least six sites on non-Federal lands along the coast. We will monitor impact of this fly, either alone or in combination with grazing or hand-pulling methods, by tracking shoot tip density, weed biomass and diversity of other plants over time, as well as by measuring the ability of protected vs unprotected Cape-ivy to regrow after grazing or pulling. The results of both cheatgrass and Cape-ivy investigations will inform implementation efforts for biological control of these weeds in forests and rangelands imperiled by fire, for protection of natural resources, forest health, and biodiversity.

We will use a combination of field-based surveys and molecular-based -omics approaches to characterize the soil microbiome across temporal and spatial gradients. We will examine changes in the soil microbiome community composition and diversity using extraction of DNA from cheatgrass root and soil samples followed by high-throughput sequencing with reference to taxonomic markers broadly used for bacteria and archaea (prokaryotes) and fungi to isolate microbial DNA and track shifts in species abundance over time and space. We will pair this in-depth sampling with metatranscriptomic approaches of known weed-suppressive strains of Pseudomonas fluorescens, including ACK55 and D7, both of which have been commercially produced and distributed. We will use long-read sequencing with Nanopore technology to assembly and compare the genomes of several strains previously shown to negatively affect cheatgrass and other invasive grasses such as medusahead to quantify changes in gene regulation linked to ecosystem functions, including carbon and nitrogen cycling, and will analyze soil nutrient composition in support of these studies. Sites in the University of California Reserve System and possibly other SPF rangeland sites will be visited twice per year for two years to account for seasonal and inter-annual variation, and both cheatgrass root and soil samples will be collected. Studies of cheatgrass under this project will be complemented by separately-funded laboratory studies, including culturing of microbes discovered as a result of sequencing, greenhouse studies of efficacy, and field application of the putative pathogenic bacterial strain ACK55. Studies of the impact of the Cape-ivy shoot tip-galling fly Parafreutreta regalis alone will involve sampling of Cape-ivy in the spring and fall in 30 small (25 x 25 cm) quadrats per site x 3 established sites to determine percent cover, shoot density and biomass as well as galling intensity and measure changes over time for at least three years. Point-intercept transects (100 m per site) will be sampled twice per year every 1 m to determine occurrence and abundance of Cape-ivy and other vegetation. To examine the effects of the fly on post-grazing or hand-pulling regrowth, one month after those physical control treatments, ten 2 x 2 m plots will be marked at each of three sites at which the Cape-ivy fly is established. If regrowth is not sufficient, 10 potted Cape-ivy plants will be placed in the ground in each plot. In five of the plots, Cape-ivy will be treated with 50% acephate granules (2 grams per pot or 20 g per m2 rate), which we have shown in greenhouse tests suppresses gall formation when applied immediately after adult oviposition. We will monitor gall density, regrowth shoot length and digitized percent cover as well as inflorescence density in a 1 x 1 m area within the 2 x 2 m plots. The results will inform implementation of biological control as a stand-alone control method or in combination with other methods.