Double-cropping strawberry (Fragaria × ananassa Duch.) and lettuce (Lactuca sativa L.) could be a sustainable alternative practice for diversified specialty crop growers. Plastic mulch is beneficial for strawberry and lettuce production with soil-biodegradable mulch (BDM) providing opportunities to reduce plastic waste generation and costs of mulch disposal. The objective of this study was to compare non-biodegradable plastic mulches and BDM to bare ground cultivation in a strawberry–lettuce double-cropping system in a Mediterranean climate. A split-plot randomized complete block design experiment with mulch treatment [non-biodegradable polyethylene (PE) film, “weedmat” (woven, PE-based), BDM, and bare ground control] as the main factor and double-cropping rotation scheme (rotation 1 or 2) as the split-plot factor was conducted between 2020 and 2021. Strawberry yield was overall greatest when mulched with BDM, PE, and weedmat compared to the bare ground control. Total soluble solids (TSS), pH, and total titratable acidity (TA) of strawberry differed due to harvest date, but only pH differed due to mulch treatment. For lettuce canopy cover, rotation 2 had greater canopy cover (86%) compared with rotation 1 (66%) 30 days after transplanting. Average head weight (0.4 kg) and head length and diameter (both 20 cm) did not differ due to mulch or rotation. Average soil temperatures under PE and BDM were ~1.5°C higher than under weedmat and 2.5°C higher than the bare ground control. Soil under weedmat had the highest moisture content, whereas the PE, BDM, and bare ground treatments had similar levels. PE, BDM, and weedmat provided equivalent weed suppression, whereas the bare ground control had the most weeds. BDM deterioration estimated as percent soil exposure (PSE) was greatest (59% PSE) by the end of the experiment, whereas PE had 18% PSE and weedmat had no deterioration. Results show that despite high levels of deterioration, BDM performs similarly to PE in terms of soil temperature and moisture modification, weed suppression, and promotion of crop growth and yield in a double-cropped system. Double-cropping strawberry and lettuce is a promising alternative for growers to diversify their crop type and with potential economic benefits by increasing mulch lifespan.

Grafting has become a common practice for watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] production in many parts of the world, due to its efficacy against biotic and abiotic stressors. However, grafting success for watermelon is challenging in part due to the complex anatomy of the cucurbit vascular system. The survival of grafted transplants depends on compatibility between the scion and rootstock, which in turn depends on anatomical, physiological, and genetic variables. A better understanding of cucurbit anatomy and graft union formation would inform grafting approaches and transplant management. An anatomical study was conducted by scanning electron microscopy (SEM) at 11 and 25 days after grafting (DAG) with seedless watermelon cultivar ‘Secretariat’ grafted onto compatible rootstock cultivars ‘Pelop’ (Lagenaria siceraria) and ‘Tetsukabuto’ (Cucurbita maxima × Cucurbita moschata) in comparison to non-grafted watermelon and rootstock seedlings. At 11 DAG, the parenchymatic cells of the central pith of grafted plants were dead and a necrotic layer was observed, representing the beginning of callus formation. New xylem strands were formed in the vascular system, connecting the rootstock with the scion. At 25 DAG, fully developed vascular bundles at the graft interface were observed with both scion-rootstock combinations. Although more studies are necessary to characterize the sequence of physiological events after grafting in Cucurbit species, this is one of the first studies to describe the complex anatomical changes that occur during watermelon graft healing.

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.

Grafting is effectively used worldwide to overcome abiotic and biotic factors impacting yield, including soil temperature. Field studies were conducted in 2020 and 2021 in a cool Mediterranean climate (average daily air temperature range of 12.8–17.1 °C) to identify suitable rootstock combinations for grafted cantaloupe (Cucumis melo var. reticulatus) and evaluate fruit yield and quality. Cantaloupe cultivars Sugar Rush (SR), Goddess (G), and Athena (A) were compatible with interspecific hybrid squash (Cucurbita maxima × C. moschata) rootstock cultivars Super Shintosa (SS) and Carnivor (CN) but were incompatible with ‘Carolina Strongback (CS)’ (Citrullus amarus) and ‘Pelop (P)’ (Lagenaria siceraria) rootstocks. Nongrafted cultivars exhibited vine decline at harvest in 2020 but not in 2021, and grafting tended to delay harvest by 15–18 days. Overall, while grafting with interspecific hybrid squash rootstocks may have delayed fruit harvest, fruit quality was not compromised. Further, yield was increased for ‘Goddess’ and ‘Athena’, but not ‘Sugar Rush’. ‘A/CN’ had the highest fruit yield/ha and number per plant. The grafted treatments of each cantaloupe cultivar with interspecific hybrid squash rootstocks met the U.S. fancy grade criteria.