By Fumiomi Takeda
The introduction of primocane-fruiting (PF) blackberries by the University of Arkansas is considered a major innovation in the blackberry industry. Anytime a variety or new way of growing a crop can extend the production and marketing season, the crop becomes more important for growers and consumers.
In addition to extending the season, this advance has expanded the commercial production of blackberries in Central America, California and other areas with mild winter conditions or in high-latitude regions with low winter temperatures. In blackberry production, winter injury is a huge concern. New cultivars and practices in PF blackberry production have enabled growers and packers to ship high-quality fresh blackberries to distant markets almost year-round in North America and to produce blackberries in areas where floricane-fruiting (FF) production has not been profitable due to winter injury. Some of these growing methods should be evaluated for growing blackberries in Florida.
Blackberry production in Florida is currently low. This has been attributed to lack of inadequate winter chill hours for production in Central Florida and areas further south. Lack of winter chill hours can cause poor and erratic budbreak in deciduous fruit crops, including blackberries.
For example, a blackberry farm near Haines City, Florida, planted recently released FF blackberries Natchez and Ouachita developed by the University of Arkansas in 5-gallon containers. These varieties produce fruit on floricanes that go through a dormant or rest period in winter and bloom and fruit the following year. The primocane development was low, and fruit production on the floricanes was less than satisfactory.
The low yield of FF blackberries grown in Central Florida is a result of low budbreak (less than 20% compared to about 60 to 70% in U.S. Department of Agriculture Plant Hardiness Zones 7 and 6) and low berry numbers per shoot (about five per shoot compared to more than eight in more northern states). In South Georgia, the same varieties have produced 15 or more fruit clusters on 6-foot tall primocanes, with each cluster producing eight or more large berries. The same FF varieties grown near Mayo in North Florida are growing vigorously and are producing ample amounts of tall primocanes with potential to produce sufficient flowering shoots and good yields.
Primocane Manipulation
Recently released PF blackberries produce fruit on current year canes and are adaptable to different production systems designed to increase their yields and produce fruit out-of-season. Their primocanes can be manipulated to produce berries in early spring or in the fall. After harvest is over, the canes can simply be cut off or mown down at ground level. This growth characteristic in PF blackberries offers growers an opportunity to produce blackberries even during winter months in areas like Florida.
To increase yields in PF blackberries, primocanes are typically tipped or topped after they reach about 3 feet in height in late spring to encourage formation of one or two branch canes from lateral buds just below the cut. If vigorously growing primocanes are not tipped then they will continue to grow upward and produce fruit only at their tips.
One study showed that in PF Prime-Ark® Traveler, the early emerged primocanes were more productive than those that emerged later in the season. Additional cane manipulation techniques, such as bending them to force subsequent growth to occur horizontally instead of growing vertically and removing leaves on the primocanes, promoted flower production and produced more fruit compared to those grown using the tipping method. (Figure 1)
The primocanes that emerged in April produced 64% more flower shoots than those that emerged after May. The late primocanes that emerged in June were not as productive as those that emerged in April, when they were bent and leaves removed produced fruit until November when remaining berries were damaged by frost.
PF blackberries can also produce fruit with less than 100 chill hours. In Prime-Ark® Freedom blackberry, research has shown that fruiting lateral numbers can be increased by bending the developing primocanes and training the primocanes to continue their extension growth horizontally. Also, these findings indicated the alternative primocane management practices of bending to orient primocanes to grow horizontally and removing the leaves increased budbreak and flower shoot emergence. Flowers begin to emerge at their tips four weeks after bud break along the entire length of bent primocanes.
Remaining Challenges
Research on PF blackberries has contributed to a better understanding of primocane emergence time and orientation, flowering relationships and how these factors improve cropping performance. Now the challenge is to force low-chilled PF blackberries to produce sufficient numbers of fruiting laterals and obtain high-quality fruit during winter at the time when strawberries are being harvested in Florida.
Other challenges for commercial blackberry production are to receive high prices for fresh fruit and to have a system to produce blackberries before or after summer months when Florida fruit is not competing with blackberries coming from Mexico.
Selecting the right PF blackberry variety and using a novel production method is another route to consider for producing blackberries in Florida.
Fumiomi Takeda (fumi.takeda@usda.gov, 304-620-5694) is a research horticulturist with the U.S. Department of Agriculture Agricultural Research Service at the Appalachian Fruit Research Station in Kearneysville, WV.