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Highbush Blueberry Cultivar Trial in Northwestern Washington

Volume 6 Issue 10

Clara TeVelde, Sean Watkinson, and Lisa DeVetter

Washington State University (WSU) Northwestern Washington Research and Extension Center



Figure 1. Clara TeVelde preparing for a blind blueberry cultivar tasting at WSU NWREC, 2017. Clara oversaw the cultivar trial in 2017 as part of her undergraduate internship experience at WSU.


New cultivars of highbush blueberry (Vaccinium corymbosum) are being developed by public and private breeding programs outside of Washington State.  While many of the important cultivars for the northwest Washington region of blueberry production have originated from breeding programs outside of Washington, cultivars still need to be evaluated for adaptability and suitability for this environment.  Furthermore, cultivar trials can begin identifying potential management issues for certain cultivars and start the process of looking at different approaches to mitigate such issues.  The Washington State University (WSU) Small Fruit Horticulture program has been conducting an initial cultivar trial for the past two years at the Northwestern Washington Research and Extension Center in Mount Vernon, Washington.  The objective of this trial is to evaluate new cultivars that have been developed outside of Washington State for potential adaptability to our unique climate in western Washington.  A secondary objective is to begin the process of extending this information to the grower community and cooperative breeding programs, so that they may have additional information regarding the performance of new cultivars.  This report presents data from the second harvest of this trial, as well as observations regarding establishment and productivity.


This cultivar trial was established in spring of 2015 as a randomized complete block design, with three-plant plots of each cultivar replicated three times (i.e., one three-plant plot per block, three blocks total).  Cultivars included in this study are: ‘Top Shelf’, ‘Blue Ribbon’, ‘Calypso’, ‘Clockwork’, ‘Last Call’, ‘Cargo’, and ‘Mini Blues’ (ORUS 10-1; formerly known as ‘Baby Blues’).  ‘Duke’, ‘Bluecrop’, ‘Liberty’, and ‘Elliott’ were also grown as experimental controls.  In 2016 and 2017, we planted ‘Mini Blues’ and an experimental huckleberry cross from Dr. Amit Dhingra (WSU Professor of Horticulture), respectively.  Blossoms were removed in the first year of growth to allow adequate plant establishment.  Plants were drip irrigated with two lines of drip tape on both sides of the plant and annually fertilized with 90 lbs N/acre (30 lbs N/acre as dry fertilizer applied pre-bloom plus 60 lbs N/acre applied via fertigation) in 2015 to 2017.  A woven-polypropylene fabric (“weedmat”) was applied over the drip tape and provided seasonal weed control.  The fabric was removed in the fall and winter months to reduce the incidence of vole (Microtus spp.) damage.  Netting for bird control was applied as the fruit began to ripen to prevent fruit loss from predation.

Plants were hand harvested in 2016 and 2017 excluding ‘Cargo’ in 2016 due to poor growth that was addressed through modified pruning and harvested this year (2017).  ‘Mini Blues’ was also not harvested in 2016, as blossoms were removed during its first year of growth, but it was harvested this year.  Total yield per plant was determined from fresh berry weights and average berry weight was estimated from a random 50-berry sample per plot.  The 50-berry sample was cooled and analyzed for firmness immediately after harvest.  Soluble solids (SS; measured as %Brix) was measured from undiluted, extracted juice with a digital refractometer (HI96801 Refractometer; Hanna Instruments, Woonsocket, RI).  Firmness was also measured on a subset of cultivars using a FirmTech II firmness tester (BioWorks, Inc., Wamego, KS).  Due to size or lack of fruit, not all cultivars were measured for firmness.

Results and Discussion:

‘Top Shelf’ had the greatest yield in 2017, followed by ‘Blue Ribbon’, ‘Liberty’, ‘Blue Crop’, ‘Last Call’, ‘Cargo’, and ‘Clockwork’ (Fig. 2).  Yields were lowest for ‘Elliott’ and ‘Mini Blues’. ‘Elliott’ failed to successfully establish across the experimental planting; we observed it was very sensitive to vole and disease pressure.  The low yield observed in ‘Mini Blues’ is attributed to the age of the plant, the smaller size of the bush, and overall smaller berry size unique to this cultivar.


Figure 2. Average yield per plant, 2017. Note ‘Baby Blues’ (ORUS 10-1) is being re-named ‘Mini Blues’.


Dates of the first harvest, firmness (g/mm of deflection), average berry weight, and SS are presented in Table 1.  Berry size was largest in ‘Top Shelf’, followed by ‘Calypso’ and ‘Cargo’.  The cultivars with the smallest berry size were ‘Mini Blues’ and ‘Clockwork’.  The small berry size in ‘Mini Blues’ was expected, as fruit from this cultivar is intended to go in the processing market where small fruit size is desirable.  During the 2017 season a blind taste test was held on August 3, 2017 at the Northwestern Washington Research and Extension Center.  Participants included faculty, staff, and graduate students.  During this tasting, it was indicated that ‘Blue Ribbon’ was the most preferred by 36.4% of participants. ‘Clockwork’ came in second place at 22.7% with ‘Bluecrop’, ‘Mini Blues’, and ‘Top Shelf’ following at 13.6% each (N= 22 Participants).  No additional cultivars were evaluated due to the time of the season and availability of other cultivars to sample.  SS is an indicator of sweetness.  SS was highest in ‘Mini Blues’ and measured 17.26%; this was followed closely by ‘Clockwork’, ‘Calypso’, and ‘Bluecrop’ (Table 1). ‘Elliott’ and ‘Cargo’ had the lowest SS averaging 13.93% and 14.11%, respectively.  Firmness data were not collected from all cultivars in this trial because berry size was too small for detection by the FirmTech.  Overall, however, it was observed that ‘Duke’, ‘Cargo’, and ‘Clockwork’ had firmer fruit than ‘Calypso’, ‘Elliott’, ‘Blue Crop’, and ‘Liberty’.

Table 1. First harvest date, fruit firmness, average berry weight, and soluble solids (SS) content of blueberry cultivars grown at the Washington State University Northwestern Washington Research and Extension Center, 2017.

Cultivar First
(g/mm of deflection)
berry weight
Soluble solids
(measured as
Top Shelf 7/25/2017 186.47 3.03 14.31
Blue Ribbon 7/25/2017 182.26 2.42 15.34
Calypso 8/21/2017 135.37 2.92 15.74
Last Call 8/21/2017 170.87 2.42 14.72
Duke 7/18/2017 219.41 1.89 15.02
Liberty 8/14/2017 145.41 2.87 14.52
Clockwork 7/25/2017 194.69 1.66 16.16
Blue Crop 8/1/2017 150.39 2.24 15.46
Elliot 8/24/2017 163.81 2.25 13.93
Mini Blues 8/1/2017 *_* 0.83 17.26
Cargo 8/14/2017 195.26 2.88 14.11

“-“ indicates no data available.
This report presents preliminary information of new cultivars that may be suitable for commercial blueberry production in northwest Washington.  As this trial continues, we will modify our management practices to better suit these new and unique cultivars.  This will allow more refined assessment of these new cultivars and their potential viability within the northwest Washington blueberry industry.  In conclusion, many of the evaluated cultivars demonstrate promise for processed and fresh-market production within the northwest Washington blueberry industry.  Continued research will provide further information regarding the adaptability and role these new cultivars will have in this important industry.


We would like to thank Jim Lovelace and Dick Mombell of Fall Creek Farm & Nursery, Inc., for provision of plants.  Additionally, we would like to thank Dr. Chad Finn, United States Department of Agriculture Agricultural Research Service, for provision of plants.  If you would like more information about cultivars available through Fall Creek, please see the following link: