Highbush blueberry (Vaccinium sp.) area in the United States increased from 22,932 ha in 2005 to 37,816 ha in 2012 (U.S. Highbush Blueberry Council, unpublished data), an average planting rate of 2125 ha/year. Northern highbush blueberries are long-lived perennial plants, requiring 7 years or more to reach full production. The cash costs to establish new plantings, through Year 6, can surpass $30,165/ha for conventional blueberry in Oregon (Julian et al., 2011).
Blueberry plantings are often established on raised beds (Strik, 2007) to help prevent saturated soils, reduce compaction, improve internal drainage (Magdoff and Van Es, 2000), and reduce disease problems such as Phytophthora root rot (Bryla and Linderman, 2007). Organic mulches are commonly used in blueberry to help control weeds (Burkhard et al., 2009; Krewer et al., 2009; Larco et al., 2013; Sciarappa et al., 2008), improve blueberry plant growth and yield (Clark and Moore, 1991; Karp et al., 2006; Kozinski, 2006; Krewer et al., 2009), root distribution through the soil profile (Spiers, 2000), and whip and shoot production (Kozinski, 2006; White, 2006).
Weed management is critical for economic production in blueberry (Pritts and Hancock, 1992; Strik et al., 1993). Pre-emergent and contact herbicides are commonly used in conventional production systems, but growers must use extreme caution when using contact herbicides during the blueberry plant-growing season to avoid crop damage.
Blueberry growers, historically, were encouraged to prune off all fruit buds to prevent fruit production in the first and second growing seasons to improve plant growth in the establishment years (Strik et al., 1993). Early cropping or allowing plants to produce fruit in the first 2 years was shown to reduce crown and root growth and fruit production in Year 3 relative to uncropped plants (Strik and Buller, 2005). However, growers experience an increased rate of return when vigorous plants are pruned to produce a limited commercial crop in Year 2 (Julian et al., 2011). Cultural practices that improve plant growth during the establishment year may lead to greater early fruit production and economic returns in blueberry.
Grow tubes (commonly called “tree shelters” in forestry) have been used successfully to improve the establishment of grape (Vitis sp.), walnut (Juglans regia L.), olive (Olea europaea L.), and landscape or forest trees (Burger et al., 1996; Famiani et al., 2007; Hall and Mahaffee, 2001; Kjelgren et al., 1997; Laliberté et al., 2008; Potter, 1988; Tuley, 1983). Grow tubes were originally developed and used in Great Britain to protect young trees from animal browsing; the use of grow tubes in commercial crop plants also offers this advantage in addition to protecting young plants from drift when contact herbicides are used to control weeds. Grow tubes have been shown to improve tree height (Bergez and Dupraz, 2000; Hammatt, 1998; Kjelgren et al., 1997; Oliet and Jacobs, 2007; Sharpe et al., 1999) and reduce suckering or branch growth (Burger et al., 1992; Hammatt, 1998), which may offer advantages in faster tree or vine establishment and a reduction in pruning costs in the establishment years. Whereas suckering is a disadvantage when establishing grapevines or many trees, an important part of establishing good blueberry bush architecture is new whip growth from the base of the plant. Root growth has been reduced in some plants when they are established with tubes, often at the expense of aboveground growth (Burger et al., 1992; Coutand et al., 2008; Famiani et al., 2007; Mayhead and Boothman, 1997; Sharpe et al., 1999; Svihra et al., 1996). Trees established with grow tubes required staking to prevent wind damage after the tubes were removed (Burger et al., 1992; Kjelgren et al., 1997).
Blueberry growers in some production regions in the western United States began using grow tubes to protect plants from mechanical or herbicide damage and from wind in the establishment year. Translucent and opaque grow tubes, commonly used by growers, differ in their effect on microclimate and temperature at the soil–mulch interface within the tube (Tarara et al., 2013). The low shortwave transmissivity of grow tubes reduced blueberry growth within the tube, but growth increased once plants grew above the tube height (Tarara et al., 2014).
The objective of the present study was to evaluate the effects of using various types of grow tubes in the establishment year(s) on plant (top and root) growth and early production of northern highbush blueberry cultivars.
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