Late Season Strawberry Production Using Day-Neutral Cultivars in High-Elevation High Tunnels

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Small-scale fruit and vegetable growers increasingly use high tunnels to expand production windows and exploit demand for local produce. Day-neutral cultivars, high tunnels, low tunnels, and targeted heating were investigated in North Logan, UT (lat. 41.766° N, 1405 m elevation, 119 freeze-free days) to extend the availability of local strawberries. Day-neutral cultivars Albion, Evie 2, Seascape, and Tribute were spring-planted in an annual hill system both inside and outside of high tunnels. Within the high tunnels, low tunnels and targeted root zone heating were tested in replicated plots. During the summer months, plastic was removed from the high tunnels and replaced with shadecloth. Treatments were evaluated for yields, fruit size, and production season. Fruit production in the tunnels began in late May and continued sporadically until December. Combinations of high and low tunnels provided more hours of optimal growing conditions than high tunnels alone, but managing the combination to maintain optimum temperatures proved difficult with temperatures often exceeding the optimum for strawberry. Targeted root zone heating efficiently increased root and canopy temperatures, preventing flower bud damage during extreme cold events, but did not significantly improve total season yields. Of the cultivars tested, ‘Evie 2’ and ‘Seascape’ had the most consistent yields and acceptable fruit size. Economic analysis indicated that growing spring-planted day-neutral strawberries in high tunnels was marginally profitable, whereas field production at this location would be a money-losing enterprise. Although the fresh market strawberry industry in the United States is overwhelmingly dominated by California and Florida, small-scale production continues throughout much of North America, particularly in proximity to urban centers where fresh local produce commands premium prices. Demand for local produce continues to increase with the developing local food movement despite environmental conditions in many areas that are less than ideal for strawberry production. Ideal conditions for strawberries occur when temperatures are between 20 and 26 °C. Suboptimal temperatures (less than 20 °C) retard the growth and development of both the strawberry plant and fruit, whereas superoptimal temperatures (greater than 35 °C) cause the strawberry plant to stop growing (Galletta and Bringhurst, 1990). Fall-planted June-bearing cultivars in an annual hill production system have proven effective for focusing fruit production in the early spring (Black et al., 2002; Poling, 1993; Stevens et al., 2011), but length of fruiting season is limited by photoperiod and temperature (Durner et al., 1984). Alternatively, day-neutral cultivars are insensitive to photoperiod and continue to flower as long as temperatures are between 4 and 29 °C (Hancock and Handley, 1998; Pritts and Dale, 1989). In many production areas including the northeast United States, day-neutral cultivars are increasingly being used to extend the growing season and produce strawberries throughout the summer. Day-neutral plants are established in the early spring, come into production near the end of the June-bearing production season, and continue to fruit through the summer and fall months (Pritts and Dale, 1989). Conditions in the high-elevation valleys of the Intermountain West region of the United States (Utah, Idaho, Nevada, western Colorado) are particularly challenging for strawberry production. Early spring temperatures are generally suboptimal and transition rapidly to summer temperatures that are typically superoptimal (Moller and Gillies, 2008). Wide diurnal temperature fluctuations in early spring also limit strawberry production in the region, and there is not sufficient water available for spring frost protection. The production window for field-grown June-bearing strawberries also coincides with peak national production and depressed wholesale prices (Pollack and Perez, 2008). The short growing season and depressed prices often make strawberry production in the region only marginally profitable. High tunnels have been successfully used to manipulate temperature and extend the growing season for a number of crops, including flowers (Rasmussen and White, 2006), vegetables (Orzolek et al., 2006), and small fruits (Demchak, 2009; Demchak et al., 2006). We previously showed that high tunnels could be used effectively in high-elevation, arid regions in the western United States to advance the production season of June-bearing strawberries with the added benefit of protecting early blossoms from frost, resulting in increased early and total yield and greater potential profitability (Rowley et al., 2010b, 2010c). Extending the production season later into the summer and fall would require day-neutral cultivars and additional temperature management strategies. Low tunnels can be used inside high tunnels to further increase temperatures for plant growth and have been used in a number of crops with varied success (McIntosh and Klingaman, 1993; Roberts and Whitworth, 1993; Takeuchi and Motsenbocker, 2005). Low tunnels are typically only 40 to 50 cm tall and cover only one row or one bed of strawberries (Galletta and Bringhurst, 1990). Replacing high-tunnel plastic with shadecloth during the warmest summer months is another method for passive manipulation of growing temperatures. The focus of this study was to optimize management systems for late-season extension of strawberry production in the Intermountain West region of the United States. Specific objectives for this study were to quantify the season extension benefits that result from using day-neutral cultivars in high tunnels, to identify a suitable day-neutral cultivar for high tunnel production, to examine temperature manipulation methods for use in combination with high tunnels to optimize growing conditions, and to examine the possibility of using summer-planted plug plants for increased fall production.

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