Blackberries are a very popular small fruit within West Virginia. However, given the variable climate of West Virginia, consistent production of quality fruit can be challenging. One option available for growers is to examine blackberry production using protected structures such as high tunnels. High tunnels also permit organic production of blackberries which can further enhance the market value of this fruit.
Several different production systems for high tunnel, organic blackberry production were examined in this project. Container production would be a suitable fit for high tunnel production, since blackberries do not produce marketable yields the first 12-18 months after establishment. Containers would allow for the plants to be moved in or out of the high tunnel as needed without tying-up valuable production space. Unlike raspberries, which have been grown successfully within containers for high tunnel production, blackberries do not perform well in container culture. It was beyond the scope of this project to understand why this is the case. However some hypotheses such as a restricted root zone, erratic media moisture and elevated root zone temperatures could be the cause. Nevertheless, it is recommended that any grower wishing to pursue high tunnel blackberry production to focus on ground culture production.
Pest management is the most critical factor for successful organic, high tunnel blackberry production. Proactive scouting and release of beneficial predators can be effective.
‘Triple Crown’, a semi-trailing, thornless blackberry variety with excellent yield and quality performed well within the high tunnel and had earlier marketable yields with less winter injury relative to open-field plots. ‘Prime Ark 45’ had excellent yield and quality, but tended to produce a lot of late fruit. Thus supplemental heat or row covers could extend the harvest season for this primocane variety. For an organic production system, the primocane fruiting cultivars may be a better choice. The canes are removed at the end of the winter so there is less labor needed for pruning flricanes relative to floricane varieties such as ‘Triple Crown’. In addition, the pest cycle of chronic pests such as spider mites is disrupted by removing the canes each season.
Blackberries (Rubus sp.) are a popular small fruit for market across West Virginia. There has been a 29% increase in acreage of blackberries across the United States since 1997 (Demchak and Elkner, 2010). Consistent commercial production in West Virginia can be risky given the variable climate of West Virginia. In West Virginia, the USDA Hardiness Zone can range from 4-6 which results in winter injury to blackberries. Fluctuating spring temperatures also promote early budbreak and risk of freeze injury. The options for growers are to choose varieties with cold tolerance such as ‘Illini Hardy’, ‘Chickasaw’ and ‘Chester’. These varieties are relatively productive, but yield and quality may not be as good as other varieties with less cold tolerance.
The second option for blackberry production in West Virginia is growing them under protected structures such as a high tunnel. High tunnels are plastic greenhouse structures which do not use electricity, heaters or fans like conventional greenhouses. Instead, high tunnels are heated by solar radiation and air movement is passive through vents. Crops within high tunnels are grown in the soil with drip irrigation used to provide water and fertilizer to the plants.
Since high tunnels exclude rainfall and accumulate heat units, marketable yield is significantly higher and there is a significant reduction in pesticide use. Organic production using high tunnels is feasible for many vegetable and fruit crops. The semi-closed environment of the high tunnel facilitates release of beneficial insects for biological pest management. The objective of this research project was to evaluate the feasibility of growing blackberries organically within a high tunnel structure in central West Virginia.
The objectives of this project were: 1) investigate the feasibility of growing blackberries organically within a high tunnel; 2) investigate organic pest management for high tunnel blackberries; and 3) investigate superior floricane and primocane fruiting cultivars for West Virginia.
A commercial-sized high tunnel (30 ft. width x 96 ft. length; Rimol Greenhouse Systems) was constructed on the Jett Farm located in southern Harrison County, West Virginia in 2008 (39.2 lat.). The high tunnel had a single layer of polyethylene plastic, and no supplemental heat was applied. Two crops of annual strawberries were grown within the high tunnel 2008-2009 (Figure 1). The soil within the high tunnel was amended with organic dairy manure compost (0.9lbs/ft2).
Two methods of growing blackberries within a high tunnel were investigated over the course of this project: ground culture of blackberries versus containerized production. Five blackberry varieties (‘Triple Crown’, ‘Prime Jan’, ‘Navaho’, ‘Kiowa’ ‘Arapaho’ and ‘Chester’) were potted in 7 gallon nursery containers filled with a 1:1 mixture of peat moss and organic dairy manure compost (Figure 2). The plants were allowed to grow one year in the outside environment within the containers adjacent to the high tunnel structure which was filled with strawberry plants. For irrigation, each pot was drip irrigated with pot drippers to provide 1.5 inches of water equivalent either by rainfall or supplemental irrigation. No additional fertilizer was applied to the plants. Nine plants were potted of each variety providing 3 replications of 3 plants each (Figure 3). In October, the containers were moved within the high tunnel to protect them during the winter. Vigor of plants within the pots was evaluated after budbreak the following spring.
To compare organic blackberry production within a ground culture system, in April 2010, 4 blackberry varieties were established within the mineral soil of the high tunnel (‘Prime Ark 45’, ‘Prime Jan’, ‘Triple Crown’ and ‘Ouachita’) (Figure 3). Each plant was spaced 3 feet apart within the row and the rows were 6.5 feet apart. Each variety was replicated 3 times with 3 plants per replication. Two drip irrigation lines were placed per row. Irrigation was scheduled using a tensiometer.
Plants were scouted for pest invasions. Bumble bees were placed within the high tunnel to promote pollination and fruit set. Beneficial insects were released if pest densities exceeded economic thresholds. In 2010-11, a T-trellis was constructed to control canopy width and facilitate harvest. Temperature (air) within the high tunnel was recorded using a Hobo data logger.
Total marketable weight and individual berry weight were measured. Brix was measured on a subsample of harvested fruit using a hand-held refractometer.
High tunnels increased the average daily air temperatures by an average of 4-7 degrees F (Figure 4). The high tunnel used for this project had a single layer of polyethylene relative to a double layer which could have increased the average daily air temperatures by ?10-12 degrees F. Blackberry cultivars were grown within containers for 24 months. Growing blackberries in containers significantly reduced vigor of the plants. Cane production (number) of container-grown blackberries relative to field plots of the same varieties was approximately 40%.
Blackberries, regardless of variety. did not grow sufficiently within containers over a 2 year period. Therefore, this experiment was jettisoned, and the plants were transplanted in open-field plots at the WVU Organic Farm near Morgantown, WV. Since container production of blackberries was not effective, the experiment focused on a smaller number of floricane and primocane fruiting varieties. ‘Triple Crown’ and ‘Prime Jan’ in addition to ‘Prime Ark 45’ and ‘Ouachita’ were planted within the high tunnel in 2010 (Figure 5). ‘Triple Crown’ is a thornless, late,semi-trailing blackberry variety which produces high quality fruit. However, this variety has shown symptoms of winter injury in West Virginia. ‘Ouachita’ is a mid-season, thornless blackberry variety with good disease resistance. ‘Prime Jan’ and ‘Prime Ark 45’ are primocane-fruiting blackberry varieties and could be used for late-season blackberry production within a high tunnel (Table 1).
Pest management is one of the most critical management issues facing high tunnel crop producers. The dry, warm environment of the high tunnel favors pest development. For organic production, routine scouting to detect pest invasions is required. Two-spotted spider mites feed on blackberry foliage with typical symptoms observed such as leaf cupping and interveinal chlorosis. The two spotted spider mite was detected within the high tunnel in April, 2011, and whiteflies were also observed in May, 2011. A 10x hand lens was useful in identifying the spider mites. Botanigard, a fungus which attacks soft bodied insects, was used to control the whiteflies and a small number of aphids. This biological fungicide was very effective in controlling the whiteflies. Organic control options for spider mites may be more challenging. Predatory mites (Phytoseiulus sp., and Neoseiulus sp.,) were used to control two spotted spider mites within the high tunnel when spider mite densities exceeded the threshold of 10-15 mites/leaf. Natural predators became common within the organically-managed high tunnel (Figure 6).
The predatory mites were effective in suppressing two spotted spider mites on blackberries within the high tunnel. However, spider mites continued to survive on the blackberry plants through early fall. Only when weather conditions became cooler did they visibly disappear.
In 2011, the first bearing year of ground culture high tunnel blackberries was recorded. ‘Triple Crown’ produced approximately 0.75 lbs. of marketable fruit per plant. Brix readings of ‘Triple Crown’ fruit was 12%. ‘Triple Crown’ in open-field plots at the WVU Organic Farm exhibited signs of winter injury on approximately 2 canes per crown. ‘Triple Crown’ grown within a high tunnel, did not show any winter injury symptoms. ‘Triple Crown’ fruit within the high tunnel was harvested beginning July 8, approximately 25 days before field plots.
‘Prime Jan’ and ‘Prime Ark 45’ began fruit maturity in late August, 2011 and harvest continued through early November (Figure 7). Both varieties produced approximately 1 lb. of marketable fruit per plant. Fruit quality of ‘Prime Ark 45’ was superior to ‘Prime Jan’ with an average brix of 12% (Figure 7). However, Prime Ark had a significant number of unripened fruit when it was finally frozen out on November 10. If supplemental heat was available, perhaps another month of harvest could have occurred with this cultivar.
- Figure 4. Mean daily temperature within the high tunnel versus ambient.
- Table 1. Blackberry varieties evaluated within a high tunnel.
- Figure 7. ‘Prime Jan’ (right) had smaller fruit relative to ‘Prime Ark 45’ (right)
- Figure 5. Blackberries were trellised within the high tunnel.
- Figure 6. Natural predators became common within the organic high tunnel.
Although this research project had partially negative results, it provided useful information on high tunnel blackberry production. One of the hypotheses was the feasibility of growing blackberries within containers. Based on recommendations for growing greenhouse/high tunnel raspberries, it would have been easy to conclude that a similar production system could work for blackberries. Blackberries have a much greater root mass relative to raspberries, and container production does not facilitate growth. This project accomplished discovering that this system is not viable and saved new growers a tremendous amount of time and capital.
Blackberries, however, can be gown successfully within a high tunnel with all the expected benefits: earliness, lateness, low disease, and winter protection. If attention is paid to early insect pest detection, organic blackberry production is extremely viable. Primocane fruiting cultivars may be a better choice for an organic production system since selective pruning is minimized and pest cycles can be broken.
Education & Outreach Activities and Participation Summary
Results from this ongoing high tunnel organic blackberry project have been extended to growers using several methods. A tour with Master Gardeners was conducted in 2010 with approximately 50 gardeners attending. Slides made from digital images of the project have been shown to commercial growers at 6 grower meetings from 2010 through December, 2011. Attendance at these meetings has been approximately 175 new and established growers from across West Virginia. In addition, the organic blackberry project at the WVU Organic Farm has been the site of 2 summer field days with over 100 gardeners and growers. Results from the high tunnel project are discussed. In 2012, a spring tour will be held at the high tunnel. Data from this project will continue to be collected and ultimately be used to create a High Tunnel Blackberry Guide.
High tunnels are becoming an indispensable tool for growing food crops in West Virginia. Over 100 high tunnel structures have been constructed in the past 3 years within West Virginia. As growers search for cropping system choices, information is crucial. There is a tremendous demand for berries including raspberries, blueberries, strawberries and blackberries. As growers attempt to fill this demand, the question of high tunnel production is asked.
Results from this project will continue beyond the length of the SARE Farmer Grant. The blackberries will remain within the high tunnel for another 3-5 years which will allow me to collect further data on yield, quality and production issues this crop. Information from this project will help direct growers to make optimal choices for variety selection and pest management. Since there has only been 1 year of yield data, we felt it was too early to create an enterprise budget for organic, high tunnel blackberry production.
Future research should focus on optimal planting arrangements for blackberries within a high tunnel. Given the limited space for cropping, what is the best planting arrangement for high tunnel blackberries? Further research needs to look at western trailing types from the Pacific Northwest. Given that ‘Triple Crown’ performs well within a high tunnel, it can be assumed most trailing varieties would also produce acceptable yield and quality.