Date of Award

Spring 5-6-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Eric Gallandt

Second Committee Member

Bryan Peterson

Third Committee Member

Gregory Porter

Additional Committee Members

John Navazio

Rachel Schattman

Abstract

Effectively managing weeds in organic vegetable production continues to be challenging and costly. Cultivation, often referred to as physical weed control (PWC), is foundational for organic farmers; however, efficacy tends to be low and highly variable. Additionally, some crops are slow to germinate, and thus have poor competitive ability against weeds and high mortality from cultivation. This can result in high costs for hand-weeding labor, abundant seed rain into the soil, and a recurring, often increasing, weed problem. These challenges may be addressed by “stacking” tools to increase weed control efficacy, integrating targeted seedbank management strategies to reduce the germinable weed seedbank, and characterizing crop cultivar early growth traits to better understand crop tolerance to different tool mechanisms. ii Chapter one reviews weed management from the perspective of small-scale organic vegetable farms and the unique challenges they face. Weed control objectives, such as minimizing weed seed rain and reducing labor costs, seed- and seedling-focused management like tarping and hand-tool options, and future research needs for small-scale farms are discussed. Chapter two assesses a weed management systems experiment combining tool stacking with seedbank management and how these practices can affect weed control efficacy and the germinable weed seedbank, respectively. Tool stacking helped increase efficacy and lower weed seedling densities during the growing season, while seedbank management reduced the germinable weed seedbank and contributed to higher crop yields in bush bean and table beet. Chapter three builds upon the previous chapter by examining how tool stacking can be used with the Terrateck Double Wheel Hoe, a unique hand tool. The effects of single tools and tool stacking on crop mortality and weed control efficacy were examined in bush bean and table beet. Tool stacking increased weed control efficacy in both crops, and although stacking did not result in higher crop mortality in bush bean, table beet mortality was high. Chapter four assesses the concept of “cultivation tolerance” with nine carrot cultivars, selected to represent large, average, and relatively small plants. Root and shoot characteristics were measured in greenhouse experiments, and carrot mortality and yield from cultivation were measured in field experiments. Few differences in early growth characteristics were found at two-true leaves, and unexpectedly, no differences in cultivar mortality were detected in the field.

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