Demand for fresh red raspberries (Rubus idaeus) by consumers in the United States has increased dramatically in the past 10 years, mirrored by an equally dramatic increase in both foreign and domestic production. Fresh raspberry movement into U.S. markets from both foreign and domestic sources grew from 98 million pounds in 2010 to 281 million pounds in 2014 (U.S. Department of Agriculture Agricultural Marketing Service, 2018). Most fresh red raspberries in North America are grown in coastal areas of California or in Mexico using a high tunnel cultivation system (Gaskell et al., 2004; Tourte et al., 2016). High tunnels allow growers to extend harvest times and produce consistently high-quality fruit in these long-season areas (Bolda et al., 2012). High tunnels provide similar benefits in regions with colder winters and shorter growing seasons (Demchak and Hanson, 2013; Hanson et al., 2011; Yao and Rosen, 2011).
Most raspberry cultivars released in the past decade are primocane fruiting, meaning they produce fruit in the autumn from the apical nodes on current-year canes, termed “primocanes” (Keep, 1961). Primocane-fruiting cultivars provide flexibility in management and fruiting times, because primocanes retained over the winter produce additional fruits the following summer from basal nodes on 2-year-old canes, termed “floricanes.” The fruiting cycle repeats as new primocanes grow and produce a second crop of fruit in the autumn. Managing plants to produce fruit on both floricanes and primocanes is termed “double cropping.”
Double cropping is common in long-season areas such as California because raspberry harvest times can be staggered and extended (Bolda et al., 2012). In areas with shorter growing seasons, raspberries grown in the open field are typically managed for primocane fruiting only, which lowers pruning, training, and trellising costs (Bushway et al., 2008). The view that floricane fruit are lower in quality than primocane fruit (Bushway et al., 2008) may also discourage growers from double cropping, even though fruit quality differences likely vary based on cultivar and seasonal weather differences (Harshman et al., 2014). In a shorter-season location in Illinois, double cropping several older cultivars doubled yields, compared with primocane-only fruiting (Skirvin and Otterbacher, 1979). In Michigan, double cropping the cultivar Heritage increased total yield only slightly over primocane-only fruiting (Hanson et al., 2011). How newer raspberry cultivars respond to double cropping is not known.
Floricane density likely affects fruit yield and quality, but optimal densities in double-cropped plants in short-season areas are not known. Twelve to 15 floricanes per linear meter of row are recommended for double cropping in California high tunnels (Bolda et al., 2012). For floricane-fruiting cultivars in short-season regions, 9 to 15 floricanes per meter of row are recommended (Bushway et al., 2008), and retaining more canes tends to increase yield but reduce fruit quality (Gundersheim and Pritts, 1991; Vanden Heuvel et al., 2000). Because floricanes compete with primocanes for light and perhaps photosynthates (Fernandez and Pritts, 1993), retaining more floricanes in double-cropped plants may reduce subsequent primocane yields.
High-tunnel raspberry production has not been widely adopted in short-season states in the Midwest and Northeast United States, even though regional high tunnel production recommendations have been developed (Pritts et al., 2017). The slow adoption likely reflects concerns over the high initial investment cost and the additional knowledge and labor that is required to manage the high tunnels and plants, as well as the recent establishment of the exotic pest spotted wing drosophila (Drosophila suzukii) (Conner and Demchak, 2018). The purpose of this study was to compare the yield potential and harvest periods of double-cropped primocane-fruiting raspberries managed with varying floricane densities in a short-growing-season area. The study was conducted in high tunnels to enhance plant vigor and managed organically because organic berry prices are generally higher than conventional prices (Tourte et al., 2016).
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