Graduation Year

2025

Graduation Month

December

Document Type

Thesis

Degree Name

Bachelor of Science

School or Department

Forestry and Conservation

Major

Environmental Science and Sustainability

Faculty Mentor Department

Ecosystem and Conservation Sciences

Faculty Mentor

Akasha Faist

Keywords

Rejuvra, annual grass, invasive species, germination

Subject Categories

Terrestrial and Aquatic Ecology | Weed Science

Abstract

Invasive annual grasses are a major driver of grassland degradation globally. In perennial grasslands, invasion can heavily impact biodiversity, including potential changes to the soil seed banks. Seed banks, the living seeds stored in the upper soil column, play an important role in healthy systems, or can harbor invasive species. To reduce negative invasion outcomes, whether in the seed bank, or aboveground vegetation, pre-emergent herbicides are a commonly used tool for land managers. Pre-emergent herbicides work by targeting seeds as they germinate and begin emerging from the soil. Thus, our study asks 1) how does pre-emergent herbicide influence germination and emergence of seeds from the soil seed bank? 2) How do pre-emergent herbicides influence the survivability of the germinates after they emerge. For this study, we employed three treatments. A control with no herbicide and two herbicide combination treatments: 1) Rejuvra and 2) Rejuvra plus Plateau combined. Rejuvra is a pre-emergent cellulose inhibitor that targets annual grasses for up to four years after application. Plateau is an acetolactate synthesis inhibitor that targets perennial and annual grass and broadleaf plants. Implementing these treatments at four field sites in northeastern Oregon, each with three 50m transects divided into three segments applied with one of the three treatments. Approximately one month after herbicide application we collected representative soil seed bank samples across the sites and treatments. Collected soils were cold treated and then planted in a greenhouse to monitor emergence and survivability rates of those emerge. Results demonstrated herbicide treatments had significantly reduced monocots and dicot emergence, and decreased survivability after emergence. Rejuvra did not target monocots, as expected, but reduced total emergence and survivability, irrespective of functional group. Reductions in germination and reducing survivability after emergence can help to deplete the seed banks of these annual species. These findings may be useful to land managers trying to restore grasslands heavily invaded by annual grass and forb species.

GLI Capstone Project

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© Copyright 2025 Blake J. Roeslein, Bryan Endress, Abby McMurtry, and Akasha Faist