Weed Management, Training, and Irrigation Practices for Organic Production of Trailing Blackberry: I. Mature Plant Growth and Fruit Production

Abstract

<jats:p>Weed management, training time, and irrigation practices were evaluated from 2013 to 2014 in a mature field of trailing blackberry (<jats:italic>Rubus</jats:italic> L. subgenus <jats:italic>Rubus</jats:italic> Watson) established in western Oregon. The field was planted in 2010 and certified organic in 2012, before the first harvest season. Treatments included two cultivars (Marion and Black Diamond), three weed management practices [nonweeded, hand-weeded or bare soil, and weed mat (black landscape fabric)], two irrigation strategies (irrigation throughout the growing season and no postharvest irrigation), and two primocane training dates (August and February). When averaged over the other treatments, ‘Marion’ and ‘Black Diamond’ had similar yields in both years. However, the presence of weeds reduced vegetative growth and yield, especially in ‘Black Diamond’, while weed mat increased growth and yield over hand-weeded plots by 13%. Withholding irrigation after harvest reduced water use by an average of 44% each year without adversely affecting yield in either cultivar. The effects of training time were primarily seen in 2014 after a cold winter. August-trained ‘Marion’ plants had more cold damage than February-trained plants and, consequently, had fewer and shorter canes, less biomass, fewer nodes, and 1 kg/plant less yield than February-trained plants. ‘Black Diamond’ was cold hardier than ‘Marion’, but was more readily infested by raspberry crown borer (<jats:italic>Pennisetia marginata</jats:italic> Harris). As the planting reached maturity, yields in the best performing organic production systems (both cultivars under weed mat and ‘Marion’ that was February-trained) averaged 11 and 9 t·ha<jats:sup>−1</jats:sup>, for ‘Black Diamond’ and ‘Marion’ respectively, similar to what would be expected in conventional production.</jats:p>

Pruning and Training Systems Impact Yield and Cold Hardiness of ‘Marion’ Trailing Blackberry

“…However, training primocanes in August (+P+F-Aug) decreased berry weight in 2000 but increased yield in 1999 and 2000 compared to training in February (+P+F-Feb). The impact of training time on yield of 'Marion' has been inconsistent in our various studies [14,16], perhaps due to differences in cultural or environmental factors.…”

“…Significant yield reduction of 'Marion' has been observed in grower fields [11] and other research trials [16] at similar temperatures. The stress and damage to primocanes that occur during training to the trellis wires are thought to increase risk of winter cold injury [9,16]. In 1999 and 2000, the lowest yield was in the industry standard of pruning out dead floricanes after harvest and training the primocanes to the trellis wires in February (Table 2).…”

“…Since the floricanes would have had time to fully remobilize nutrients by October 30 (+PlF), the likely reason for the unpruned treatment (+P+F) to have greater yield in 1997 is less training damage to primocanes. It is important to train primocanes carefully to the trellis wires to avoid kinking or damage, which reduce subsequent yield [9,16]. When primocanes either grew up through the canopy of the floricanes or could be trained over the dead floricane canopy, there was less training damage (personal observation).…”

“…'Marion' blackberry is relatively sensitive to winter cold injury because it has a low chilling requirement [36] and can experience cane or bud damage at temperatures at −5 to −22 • C [12,13]. Significant yield reduction of 'Marion' has been observed in grower fields [11] and other research trials [16] at similar temperatures. The stress and damage to primocanes that occur during training to the trellis wires are thought to increase risk of winter cold injury [9,16].…”

“…Bell et al [14] theorized that training primocanes in August improved the light exposure and carbohydrate status of the primocanes, compared to leaving canes on the ground most of the winter and training in February, thus increasing subsequent bud break. Flower bud initiation and differentiation occur in early autumn in trailing blackberry [15]; good light exposure during this period has improved the number of flowers per lateral in 'Marion' in some cases [14] but not others [16].…”