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Sweetpotato (Ipomoea batatas) production in the northern United States is limited due to the perceived barriers of a short growing season and relatively cool summer temperatures, yet recent studies have shown yield in northern regions can be greater than the national average when sweetpotatoes are grown with plastic mulch. A study was conducted in northwest Washington to evaluate the productivity of ‘Covington’ sweetpotato with polyethylene (PE) and soil-biodegradable (BDM) mulches and different in-row spacings (20, 30, and 38 cm) in 2019, and to test accessions resistant to wireworm (Agriotes sp. and Limonius sp.) in 2020. In 2019, slips were shipped from North Carolina, and after 4 days in transit, 60% to 70% died after transplanting in the field. By the end of the season, BDM deterioration reached 11% compared with 0.4% for PE mulch, but there were no differences due to mulch in plant establishment, growth, yield, or the proportion of storage roots damaged by wireworm. Total storage root yield was 22 t⋅ha⁻¹ with PE mulch and 15 t⋅ha⁻¹ with BDM. Percent canopy cover was greatest at 20-cm spacing later in the growing season, likely due to intermingling of vines from adjacent plants, whereas high percent canopy cover at 38-cm spacing was likely due to increased production of secondary vines per plant. Total yield was greatest with 20-cm plant spacing (20.4 t⋅ha⁻¹), intermediate with 30-cm spacing (18.0 t⋅ha⁻¹), and lowest with 38-cm spacing (17.0 t⋅ha⁻¹). In contrast, the greatest number of storage roots per plant was produced with 38-cm plant spacing (3.4). There were more jumbo sweetpotatoes produced with PE mulch (3.4 t⋅ha⁻¹) and with 30-cm spacing (3 t⋅ha⁻¹), and the weight of U.S. No. 2 grade sweetpotatoes was greatest at 20-cm spacing (10.2 t⋅ha⁻¹). Soil temperature was increased by 3 °C under the PE mulch and 2 °C under the BDM compared with bare ground. However, 98% of storage roots were observed to be severely damaged by wireworm in 2019, with more than 10 to 20 holes per storage root. For wireworm-resistant accessions in 2020, 16% of the storage roots were damaged by wireworm, with 1.7 to 4.0 holes per storage root. Total yield of accessions PI 666141 and 04-791 (45.5 t⋅ha⁻¹ on average) was greater than the national average (24.7 t⋅ha⁻¹). Overall, sweetpotatoes appear to be suitable for production in northwest Washington, but low yield in 2019 highlights the importance of healthy slips for successful production. Future research should evaluate cultivars with maximum adaptation to the region, techniques to reduce wireworm damage including genetic resistance, and the economics of producing sweetpotatoes in northern regions.

The use of polyethylene (PE) mulch causes environmental pollution where incomplete removal leaves fragments susceptible to escape to ecosystems, such as the ocean, where they can cause ecological harm. PE mulch is generally nonrecyclable due to contamination with soil and crop debris after use, leaving growers with few end-of-life options for used PE mulch. Research studies have shown that soil-biodegradable plastic mulch (BDM) is comparable to PE mulch in terms of performance, soil health, and overall economics and is preferred from an environmental perspective, but the adoption of BDM by producers is still low. Previous research has shown that the primary barriers to BDM adoption are insufficient knowledge about BDM, high purchase cost, and unpredictable breakdown of BDM in the soil. The high purchase cost of BDM compared with PE mulch is offset by the costs for PE mulch removal, transport, and disposal fees. This project was conducted to develop BDM training materials, to educate and assess BDM knowledge gained by extension personnel and other agricultural professionals through trainings and webinars, and to educate producers about BDM through hands-on experience. Thirty-six research and extension publication outputs from two previous US Department of Agriculture Specialty Crop Research Initiative BDM projects were reviewed and transcribed into 45 new extension publications that included 11 slide presentations, 5 lecture slides, 10 fact sheets, and 3 videos. All the training materials are posted on a public university website. Professional development trainings were conducted at local, regional, national, and international levels to provide agricultural professionals the current, science-based information on BDM and resources for information. Survey results showed that at a local level, the greatest change of knowledge among participants was observed for “BDM use in organic production” (60%), and the lowest reported change of knowledge was observed for “limitations to PE mulch disposal” (19%). At a regional level, out of 58 participants, 23% to 35% of participants learned “a lot” and 35% to 51% learned “some new information” regarding BDM from the webinar. At the national level, out of 30 participants, 48% responded that they learned “a lot” and another 48% learned “some new information” on BDM from the training. Growers were trained about BDM via field days and on-farm demonstrations where five strawberry (Fragaria ×ananassa) growers volunteered to participate in BDM trials. The participant growers observed no difference in weed control and fruit yield between the PE mulch and the BDM. Growers expressed concerns about slow biodegradation of BDM after soil incorporation, potential impacts on soil biological activity, food safety concerns with BDM fragments and that BDM is not currently permitted for use in organic production.