Dissertation
NATURAL ORGANIC REGISTERED HERBICIDES AND THEIR USE IN THE DRYLAND INLAND PACIFIC NORTHWEST
Doctor of Philosophy (PhD), Washington State University
2025
Abstract
Weed management is often the greatest production challenge for farmers, whether conventional, no-till, or organic, in the inland Pacific Northwest (iPNW). This dissertation investigates the use and effectiveness of two plant-derived herbicides, registered for use in certified organic production under United States Department of Agriculture organic standards, with different active ingredients–capric and caprylic acid (CAP) and d-limonene (LIM)–to combat weeds in the iPNW. After the Introduction (Chapter 1), Chapter 2 examines in field plot studies the use of CAP, LIM, and winter peas (Pisum sativum L.), in controlling weeds. Both CAP and LIM controlled weeds similar to mechanical control (MECH) and did not affect soil pH, nutrient cycles, or pea weevils. The cost to apply CAP and LIM was found to be prohibitive to use as a main form of weed management in the grain rotation systems of the iPNW. However, CAP and LIM may be best used for spot spraying difficult weeds already resistant to commonly used herbicides in the iPNW.
In greenhouse studies, Chapter 3 addresses questions and concerns about plant back intervals (the minimum time that must pass between a pesticide application and planting the next crop) for CAP and LIM and their effect on soil pH. CAP could be used up to a day before emergence without inhibiting germination or emergence, whereas LIM reduced emergence of wheat (Triticum aestivum) and pea (Pisum sativum) throughout the study. Neither of the herbicides acidified the soil.Chapter 4 evaluates the sensitivity of major iPNW field crops, such as wheat and pea, and weeds to three different labeled concentrations of CAP and LIM in a greenhouse study. CAP and LIM were compared to MECH. CAP mixed at the highest labeled concentration caused similar plant death to MECH for all large weeds except Italian ryegrass (Lolium multiflorum). Nearly all concentrations of CAP and LIM caused less regrowth of large rattail fescue (Vulpia myuros) than MECH.
Natural herbicides, such as CAP and LIM, certainly have their benefits but are currently too costly for large-scale use in the iPNW. If they can become more cost-effective, iPNW farmers would likely use them.
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Details
- Title
- NATURAL ORGANIC REGISTERED HERBICIDES AND THEIR USE IN THE DRYLAND INLAND PACIFIC NORTHWEST
- Creators
- Aaron Blaine Appleby
- Contributors
- Lynne A. Carpenter-Boggs (Advisor)John P. Reganold (Committee Member)Karen A. Sanguinet (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Crop and Soil Sciences
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 148
- Identifiers
- 99901357689401842
- Language
- English
- Resource Type
- Dissertation