About 6000 ha of blackberry (Rubus L. subgenus Rubus, Watson) was harvested in the United States in 2012 [U.S. Department of Agriculture (USDA), 2014]. Oregon was the leading producer with 2500 ha, most of which were trailing types grown predominantly for the processed market (Strik and Finn, 2012; USDA, 2014). There were only 200 ha of organic blackberry harvested from certified and exempt organic farms in the United States in 2008, although worldwide production was 2500 ha (Strik et al., 2008; USDA, 2010). Consumer demand for organic products has been steadily increasing, creating a price premium for organic fruit and strong interest in organic production systems.
There is a growing body of research dedicated to blackberry growth and production (e.g., Strik and Finn, 2012), but there has been relatively little published on the organic production of blackberry. The Appropriate Technology Transfer for Rural America has published a general organic production guide that is mainly focused on small-scale production of erect and semierect types of blackberry for the fresh market with little information on the production of trailing types for the processed market (Kuepper et al., 2003). In organic trailing blackberry systems, Harkins et al. (2013, 2014) studied weed management and cultivar impacts during establishment, and Fernandez-Salvador et al. (2015a, 2015b) investigated several cultivar and fertilizer options.
Weed management can be one of the most challenging and expensive issues to address in organic production, as Organic Materials Review Institute (OMRI)-listed materials for weed control are limited, and removing weeds by hand is expensive. Therefore, some growers allow weeds to grow in organic blackberry plantings and remove them only before harvest. However, weeds compete with blackberry plants and can significantly reduce yield when left unmanaged (Harkins et al., 2013; Meyers et al., 2014). The use of a perforated landscape fabric, or “weed mat,” as a barrier to weeds within the blackberry row has been successful in blackberry plantings during establishment (Harkins et al., 2013; Makus, 2011; Meyers et al., 2014).
Most of the research published to date on trailing blackberry has been in ‘Marion’ or other older cultivars (Bell et al., 1995a, 1995b; Cortell et al., 1997a, 1997b; Julian et al., 2009; Mohadjer et al., 2001; Sheets et al., 1972; Takeda et al., 2002). However, many newer thornless cultivars, such as ‘Black Diamond’, are desirable to producers because they reduce training time and cane damage and eliminate the risk of finding thorny petioles in the machine-harvested, processed end product (Strik and Buller, 2002). Thornless cultivars of trailing blackberry are also reported to be cold hardier (Finn et al., 2005). ‘Marion’ and ‘Black Diamond’ together accounted for >75% of the 2914 ha of blackberry produced in Oregon in 2012 (USDA, 2013).
Trailing blackberry canes are typically trained onto a two-wire trellis in either late summer or late winter. Bell et al. (1995a) found that ‘Marion’ plants trained in August produced 46% greater yield than those trained in February. Despite the potential increase in yield, many growers still train in February, as canes left on the ground through the colder winter months are better protected from cold damage (Bell et al., 1992).
Irrigation practices in blackberry are varied. Most fresh market plantings are irrigated by drip irrigation, while blackberry grown for processed markets are most commonly irrigated using moveable pipe with overhead sprinklers or big gun systems (Strik and Finn, 2012; B.C. Strik, personal observation). Some growers in Oregon do not irrigate at all, even though blackberry plants have high water demands during fruit production (Bryla and Strik, 2008; Strik and Finn, 2012) and there is relatively little precipitation in summer (U.S. Department of Interior, 2013). There may be an option for an intermediate solution of turning off irrigation to blackberry after harvest instead of irrigating throughout the summer because irrigation demand drops off after fruit production (Bryla and Strik, 2008). Drip irrigation may be especially beneficial in organic production by reducing weed presence outside the drip zone and disease problems in the canopy when compared with overhead systems. Applying fertilizers through the drip irrigation system (fertigation) has worked well using OMRI-approved products in organic blackberry (Fernandez-Salvador et al., 2015a).
The objective of this study was to evaluate various production practices (cultivar, weed management, training time, and irrigation) for their effect on growth and organic production of mature trailing blackberry that were machine-harvested for the processed market. Two cultivars, ‘Marion’ and ‘Black Diamond’, were included in the study, along with three weed management strategies, nonweeded, hand-weeded, and weed mat. Two training dates, August and February, and two irrigation strategies, continuous summer irrigation and no irrigation after fruit harvest, were also included.
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