Date of Graduation

5-2024

Document Type

Thesis

Degree Name

Master of Science in Horticulture (MS)

Degree Level

Graduate

Department

Horticulture

Advisor/Mentor

Dickson, Ryan W.

Committee Member

Worthington, Margaret L.

Second Committee Member

Burnett, Stephanie

Third Committee Member

McWhirt, Amanda L.

Keywords

blackberry; floricane; growing degree day; heat unit; long cane; primocane

Abstract

Consumer demand for locally produced and high-quality blackberries is projected to increase. Most blackberry production is field-based, however, there is interest in producing blackberries using soilless culture and “long-cane” technique, where plants are grown in containers and trellised vertically. Soilless “long-cane” production of blackberries is viewed as a possible solution to the yield losses caused by soilborne pathogens such as Fusarium oxysporum, and methods of soil-borne pathogen control have become increasingly difficult with the ban of methyl bromide, a highly effective and widely used but environmentally harmful soil fumigant. Other reported benefits of soilless caneberry production include greater yields, increased harvest labor and resource efficiency, and the ability to schedule off-season harvests. Soilless production often occurs in protected environments (i.e. greenhouses, plastic high tunnels) which can be used to achieve off-season production for early spring and late fall markets. However, little research has been conducted to evaluate the potential of long-cane blackberry systems. This study evaluated the crop timing and yield potential of blackberry cultivars grown as long-canes and forced to flower and fruit under different environmental conditions. A separate objective was also to generate baseline information to assist growers in developing and managing long-cane systems. In the first experiment, four blackberry cultivars ('Natchez', 'PrimeArk ® Freedom', 'Ouachita', and 'Prime-Ark ® Traveler') were grown using long-cane technique and exposed to different cold storage and forcing environment strategies. Cold storage strategies consisted of allowing blackberry plants to fulfill dormancy requirements by either overwintering on an outdoor nursery area (USDA Plant Hardiness Zone 7a) or by being placed in a cold storage facility at 4°C. Forcing strategies consisted of placing dormant plants in either a heated greenhouse or outdoor nursery area in early or late spring for the development (i.e., “forcing”) of flowers and fruit. In the second experiment, eight blackberry cultivars (‘Loch Ness’, ‘Ouachita’, 'Natchez', ‘Osage’, ‘Ponca’, 'Prime-Ark ® Freedom', ‘Prime-Ark ® 45’, and 'Prime-Ark ® Traveler') grown as long-canes by a commercial long-cane producer were shipped dormant to the University of Arkansas and forced in both a greenhouse and high tunnel in early spring. To the author’s knowledge, this is the first study to track heat unit accumulation and quantify the thermal energy requirements for long-cane blackberry. The accumulation of heat units (measured as degree days) by cultivars at first flower and first ripe fruit were similar between production strategy treatments despite large differences in crop time (i.e., days to flower and/or fruit), suggesting cultivars had predetermined and consistent thermal energy requirements to reach these stages of development. Long-cane blackberry growers can use the heat unit information generated by this study to track plant development during production and predict harvest dates, which is common for field-grown blackberry and other crops. Overall, the marketable yield across cultivars and strategies was considered sub-optimal for commercial production, except as was observed with ‘Loch Ness’, which produced 3.6 kg∙plant-1 in the second experiment. Storing dormant long-canes at 4°C had no negative effects on yield compared to overwintering outdoors. Total harvested fruit (marketable and unmarketable fruit) was much greater (sometimes up to 5× greater) than the amount of marketable fruit harvested for certain treatments and cultivars, and potential causes of high unmarketable fruit percentages is discussed more in Chapter 2. Treatments where plants developed fruit under higher light and temperature conditions, for example forcing outdoors and later in spring, resulted in the greatest total fruit production and emphasized the impact of environmental factors on fruit yield. The greenhouse and high tunnel environments slightly improved the percentage of marketable fruit harvested, but also reduced sunlight transmission and total fruit yields compared to plants grown outdoors. The methods used to produce long-cane blackberry plants prior to dormancy have a major influence on yield and may have influenced yields in this study. Since the start of these experiments, the commercially standard practices for producing long-canes have evolved to result in improved yields, and the author expects the cultivars used in this study would have greater yields than reported using the new and current practices. Long-cane blackberry production shows promise as a strategy to minimize soil borne root diseases and schedule off-season production. However, proper cultivar selection and optimization of the protected structure, environmental parameters (mainly temperature and light), and cultural practices are necessary for these systems to be high-yielding and profitable.

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