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JORDAN WHITE THESIS
Embargoed Access, Embargo ends: 01/16/2027
Thesis
Putting down roots: growing sweetpotato with unique traits and plastic mulch in northwest Washington
Master of Science (MS), Washington State University
2026
Abstract
Two experiments were carried out in 2024 and 2025 at the Northwestern Washington Research and Extension Center in Mount Vernon, WA to assess production potential of sweetpotato [Ipomoea batatas (L.) Lam.], a nutritious and low-input crop new to the region. The first experiment evaluated resistance to wireworm (Agriotes lineatus, A. obscurus, and Limonius canus) using the wireworm-Diabrotica-Systena (WDS) severity index (0–4 rating). Cv. Cascade had the highest resistance (1.19 rating), and six USDA advanced breeding lines and cv. Covington had medium to high WDS ratings (1.93–3.02), indicating low to no resistance. Total and potential marketable yield of cv. Covington (22,712 kg.ha-1 and 18,111 kg.ha-1, respectively) were almost 2 times greater than other entries, indicating a need to improve yield of wireworm resistant cultivars. The second experiment assessed sweetpotato yield from 8 to 18 weeks after transplanting (WAT) with and without black polyethylene (PE) mulch. Total yield increased 1.3–1.9 times with PE mulch and 1.4–2.9 times with bare soil every 2 weeks from 10 to 18 WAT, and total and marketable yield were double with PE mulch (19,738 kg.ha-1 and 16,671 kg.ha-1, respectively) compared with bare soil (6,356 kg.ha-1 and 4,739 kg.ha-1, respectively) at final harvest. PE mulch increased soil temperature by ~1.8 °C on average throughout the growing season, and growing degree days (GDD) based on soil temperature with PE mulch was 20% greater with 10 °C base temperature (Tb) and 47% greater with 15.5 °C Tb than GDD based on bare soil temperature by the end of the growing season. GDD 10 °C Tb appears to be most suitable in northwest Washington as sweetpotato growth continued between 10 and 15 °C. Our findings show that PE mulch is essential to high yields in northwest Washington, and that there is a need for high-yielding wireworm resistant cultivars.
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Details
- Title
- Putting down roots: growing sweetpotato with unique traits and plastic mulch in northwest Washington
- Creators
- Jordan White
- Contributors
- Carol Miles (Advisor)Jacob Blauer (Committee Member)Gabriel LaHue (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Horticulture
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Number of pages
- 99
- Identifiers
- 99901393305501842
- Language
- English
- Resource Type
- Thesis