Commercial production of northern highbush blueberry (Vaccinium corymbosum) is dependent upon rented colonies of honey bees (Apis mellifera) for meeting pollination requirements. Despite the prevalent use of honey bees, growers in Washington State and the greater Pacific Northwest (PNW), particularly those located in the western regions, claim pollination is limited and yield potential is subsequently reduced due to pollination deficits. However, there have been no studies or surveys that document this occurrence for this economically important region of blueberry production. The objective of this study was to survey honey bee activity in commercial plantings of ‘Duke’ highbush blueberry in western and eastern Washington and to assess the relationship between honey bee activity, growing region, and select yield components. Honey bee colony strength was also assessed to evaluate this variable’s relationship to honey bee activity and measured yield components. Sixteen and 18 commercial ‘Duke’ blueberry fields across Washington State were surveyed in 2014 and 2015, respectively. Average number of honey bee visitations per plant and honey bee colony strength were determined to evaluate overall honey bee activity. Estimated yield, berry number per plant, berry size (mass), and seed number per berry were also determined and analyzed to determine their relationship to honey bee activity through regression analysis. Honey bee visitation rates differed between western and eastern Washington, with western Washington sites consistently below recommended honey bee densities. Colony strength was also below recommended levels, but was lower for western Washington relative to eastern Washington. Estimated yield and berry number differed across sites and years, but were not related to honey bee visitation rates. Regression analysis revealed few significant relationships, although honey bee visitation rates were positively related to seed number per berry and seed number was positively related to berry size (R 2 = 0.25 and 0.16, respectively). Berry size was also positively related to colony strength (R 2 = 0.63). This study demonstrates that honey bee activity is limited in Washington blueberry production, particularly in western Washington, when compared with recommendations for optimal honey bee activity in blueberry. However, yields were unaffected between the compared regions. The lack of a relationship between honey bee visitation rates and yields suggests that pollination is sufficient for ‘Duke’ blueberry in Washington State and pollination deficits do not limit yield for this cultivar under the conditions of the study.
Lisa W. DeVetter, Sean Watkinson, Ramesh Sagili, and Timothy Lawrence
Lisa W. DeVetter, David Granatstein, Elizabeth Kirby, and Michael Brady
Global production of highbush blueberry (Vaccinium corymbosum) has continuously increased since the early 1990s, with substantial growth occurring after 2000. Benefiting from this growth is the organic blueberry (Vaccinium sp.) industry, which has been strengthened by increases in organic food sales and the price premiums received for organic products. Washington State is a national and global leader in organic blueberry production, with 47% of the national organic blueberry crop harvested in 2008. As this statewide industry continues to grow, it is important to recognize both the opportunities and challenges related to organic blueberry production and marketing. This paper addresses those issues and describes trends in organic highbush blueberry production using Washington State as a case study due to its scale and distinctive regional differences within the state in regard to climate, horticultural production, and market venues. Challenges related to the introduction and management of new diseases and pests, changes in the federal organic regulations, infrastructural limitations, and climate change threaten current production capabilities in Washington State. However, the industry is still poised to capitalize on organic blueberry markets and has a lower market risk in the medium term compared with other crops.
Rachel E. Rudolph, Thomas W. Walters, Lisa W. DeVetter, and Inga A. Zasada
One of the primary production challenges red raspberry (Rubus idaeus) growers in the Pacific northwestern United States confront is root lesion nematode [RLN (Pratylenchus penetrans)]. In this perennial production system, red raspberry serves as a sustained host for RLN. When a red raspberry planting is slated for removal in the fall, a new red raspberry planting quickly follows in the same field the following spring. The primary crop that occurs in rotation with red raspberry is a winter wheat cover crop to provide soil coverage and protection during the winter. The objectives of this research were to determine if winter wheat (Triticum aestivum) provides a green bridge for RLN in continuous red raspberry production systems and to determine if modified winter cover cropping practices can be used to reduce population densities of RLN before replanting red raspberry. Four trials were established in fields being replanted to red raspberry and the following modified winter cover cropping practices were considered: cover crop planting date (at fumigation or 2 weeks after fumigation), termination date (cover crop kill with herbicide 2 or 6 weeks before incorporation compared with the industry standard of incorporation immediately before planting), and the additional application of methomyl. ‘Rosalyn’ and ‘Bobtail’ winter wheat planted as cover crops in these trials were demonstrated to be maintenance hosts for RLN (ranging from 10 to 947 RLN/g winter wheat root across trials) allowing them to be a green bridge for RLN to infect the following red raspberry crop. Altering winter wheat cover crop planting date, termination date with herbicide, or methomyl application did not affect RLN population densities in the subsequent red raspberry crop. Although planting an RLN maintenance host may be of concern to growers, the advantages of reduced soil erosion and nitrate leaching associated with cover cropping outweigh the perceived risk to the subsequent red raspberry crop.
Rachel E. Rudolph, Lisa W. DeVetter, Inga A. Zasada, and Cedar Hesse
Cover crops can lessen soil erosion and compaction, improve water infiltration, enhance nutrient availability, suppress weeds, and assist with pest management. However, cover crops are not commonly used in alleyways of established red raspberry (Rubus idaeus) fields in the Pacific Northwest of the United States. Rather, the space between red raspberry beds is repeatedly cultivated and the soil is kept bare, which has detrimental effects on soil quality. Adoption of alleyway cover crops is limited because red raspberry growers are concerned about resource competition between a cover crop and red raspberry crop. A 2-year study was conducted in an established ‘Meeker’ red raspberry field in northwest Washington to evaluate the effects of eight annually seeded alleyway cover crops (cultivars of wheat, cereal rye, triticale, oat, and ryegrass), one perennial ryegrass alleyway cover crop, mowed weed vegetation, and the industry standard of cultivated bare soil (Till) on the physical, chemical, and biological properties of soil quality in alleyways and raised beds. This included evaluating soil bulk density (D b), compaction, organic matter, pH, cation exchange capacity (CEC), macro- and micronutrients, and bacterial and fungal community structure; red raspberry yield and fruit quality were also evaluated. Although there were statistically significant differences among treatments across sampling dates for CEC, there were no consistent trends. Alleyways planted with the perennial ryegrass mix had the lowest mean D b 6 and 24 months after seeding. Tilled alleyways had the lowest D b 12 and 18 months into the study. Red raspberry grown adjacent to Till did not result in a significantly higher estimated yield or fruit total soluble solids than raspberry grown adjacent to cover crops in either year of the experiment. Differences in microbial community structure were observed among seasons rather than treatments. These results do not demonstrate significant effects of alleyway cover crops on red raspberry productivity when applied to established fields. The potential benefits of alleyway cover cropping on soil quality may outweigh any concerns regarding resource competition. Changes in soil quality are often difficult to quantify and require long-term study.
Lisa W. DeVetter, Huan Zhang, Shuresh Ghimire, Sean Watkinson, and Carol A. Miles
Day-neutral strawberry (Fragaria ×ananassa) is typically grown in plasticulture production systems that use black polyethylene (PE) mulch for weed management and promotion of crop growth and yield. The objectives of this research were to evaluate several commercial plastic and paper biodegradable mulch (BDM) products [Bio360, Experimental Prototype (Exp. Prototype), and WeedGuardPlus] in comparison with standard black PE mulch and bare ground cultivation in day-neutral strawberry grown in an annual system in northwestern Washington. Mulch performance [as percent visual cover (PVC)], weed suppression, marketable yield, plant biomass, and fruit quality were evaluated in ‘Albion’ and ‘Seascape’ strawberry grown in 2014 and 2015. PVC measured at the end of the production season was lowest for the Exp. Prototype (8%) in 2014 and was greatest for Bio360 (90%), WeedGuardPlus (90%), and PE (98%). In 2015, PVC at the end of the production season was again lowest for Exp. Prototype (62%), followed by WeedGuardPlus (64%), Bio360 (93%), and PE mulch (97%). Overall, weed pressure was higher in 2015 relative to 2014 and was greatest in the bare ground treatment in both years of the study. By the end of the 2015 season, weed cover in the bare ground treatment was 95%, followed by WeedGuardPlus (50%), Exp. Prototype (34%), PE (25%), and Bio360 (15%). Yield showed year and cultivar effects and was higher in mulched treatments. Plant biomass showed varying effects; root biomass was lowest in ‘Seascape’ in 2015 under the bare ground treatment and greatest under Bio360, which was similar to PE mulch and WeedGuardPlus. Leaf biomass was lowest in the bare ground treatment and highest in mulched treatments (except in 2015, when leaf biomass was intermediate for plants grown with WeedGuardPlus). Crown biomass showed a similar trend and was overall greater for plants grown in mulched treatments except for Bio360 in 2014, which was the same as the bare ground treatment. Overall, fruit quality was maintained among strawberry grown with BDMs, with soluble solids concentration (SSC, %) and titratable acidity (TA) being the only variables to show treatment effects. SCC tended to be lower in fruit from bare ground plots. TA was different for ‘Seascape’ in 2015 with fruit from bare ground and Exp. Prototype treatments having higher TA than the PE treatment. This study demonstrates that BDMs can be comparable to PE mulch in terms of performance and impacts on crop productivity in day-neutral strawberry, suggesting that BDMs could be a viable alternative to PE mulch for strawberry growers in the Pacific Northwest.
Fan-Hsuan Yang, Lisa W. DeVetter, Bernadine C. Strik, and David R. Bryla
Accumulation of calcium (Ca) in fruit is largely caused by transpiration and varies depending on the concentration of Ca in the xylem fluid. The objective of the present study was to evaluate the relationship between fruit stomatal functioning and Ca accumulation during different stages of development in northern highbush blueberry (Vaccinium corymbosum L.). Stomata were scarce on the berries and were concentrated primarily on the distal end near the calyx. The density of the stomata was greatest at petal fall, averaging 5 to 108 stomata/mm2 from the proximal end (pedicel end) to the distal end of the berries. Stomata were wide-open at the early green stage of berry development and had a slight deposit of wax along the guard cells. As the berries expanded during the initial period of rapid growth (stage I), most of the stomata remained near the distal segment of the berries; by the late green stage, almost none was found in the middle and proximal segments. The majority of these stomata were completely covered with wax when the berries began to change color and ripen (stage II and stage III). Stomatal conductance (g S) of the berries averaged 45 mmol·m−2·s−1 at petal fall and rapidly declined as the fruit developed. By the fruit coloring stage, conductance was low and remained less than 15 mmol·m−2·s−1 throughout the ripening period. In four cultivars, including Duke, Bluecrop, Aurora, and Elliott, Ca uptake in the berries increased rapidly during the early green stage; however, it slowed considerably between the late green and fruit coloring stages and stopped completely during fruit ripening. The results of this study strongly suggested that practices used to increase the Ca content of blueberries, such as the application of foliar fertilizers, should be performed early in the season during the first few weeks after flowering.
Rachel E. Rudolph, Lisa W. DeVetter, Chris Benedict, and Inga A. Zasada
A survey was conducted in Washington State in 2015 and 2016 to gauge grower perceptions, understanding, and current practices regarding soil quality. Soil quality has been defined as the ability of the soil to sustain plants, animals, and humans over time. Many current practices of modern agriculture can be detrimental to soil quality, including soil tillage and soil fumigation, both of which are commonly used for the Washington red raspberry (Rubus idaeus) production system. The area between red raspberry beds, known as the alleyway, is frequently tilled and kept bare, without groundcover, to manage weeds. Growers commonly fumigate the soil before planting red raspberry to manage soilborne pathogens and plant-parasitic nematodes. The majority of red raspberry growers surveyed consider soil quality quite often in relation to the management of their fields. The majority of growers during both years considered cover crops to have a positive impact on soil quality. However, growers also perceived soil fumigation to have a positive impact on soil quality. The majority of growers responded that they were willing to adopt alleyway cover crops for a variety of reasons, including improving red raspberry production, physical soil quality, and beneficial soil microorganism populations. This survey demonstrated that there is interest in soil quality among growers; however, there is a difference in perceptions between growers and researchers regarding how management practices impact soil quality.
Jessica R. Goldberger, Lisa W. DeVetter, and Katherine E. Dentzman
Although agricultural plastic mulches can have significant horticultural benefits for specialty crops such as strawberry (Fragaria ×ananassa), there can also be significant economic and environmental costs. In particular, polyethylene (PE) plastic mulch requires labor and financial investments for removal and disposal. Micro- or nanoparticles may persist in soil and negatively affect microbial activity, physical soil properties, and nutrient availability. A possible alternative to PE mulch is biodegradable plastic mulch, which has similar horticultural benefits but does not need to be removed from the field at the end of the growing season. Biodegradable plastic mulch can be tilled into the soil, where it is converted by soil microorganisms into water, carbon dioxide, and microbial biomass. Although horticultural and environmental research into the impacts of PE and biodegradable plastic mulch is ongoing, it is also important to understand farmers’ practices and perceptions related to these mulches. We conducted a survey of strawberry growers in three growing regions of the United States: California, the Pacific Northwest, and the Mid-Atlantic. Our results indicate several regional differences, with California farmers being more likely to have used biodegradable plastic mulch, and growers from California and the Pacific Northwest being more likely to perceive negative impacts of PE mulch compared with growers in the Mid-Atlantic. Regardless of region, a majority of growers were interested in learning more about biodegradable plastic mulch. We conclude with several suggestions for biodegradable plastic mulch development and outreach that may promote strawberry growers’ adoption of this technology.
Amit Bhasin, Joan Davenport, Scott Lukas, Qianwen Lu, Gwen Hoheisel, and Lisa W. DeVetter
Bloom to fruit maturity is a period of rapid growth and nitrogen (N) uptake in northern highbush blueberry (Vaccinium corymbosum L.). Sufficient plant-available N is critical during this time, and growers often accomplish this through fertilizer applications from bloom through fruit development. For organic production in northern climates like Washington State, postharvest applications of N fertilizer are not recommended for northern highbush blueberry because they may stimulate excessive vegetative growth, reduce floral bud set, and increase the risk of winter injury through delayed acclimation. However, early fruiting cultivars with the potential for an extended growing season after harvest may benefit from postharvest N applications because the additional N may promote shoot and root growth that could support fruit production in future years while still allowing plants to form floral buds and acclimate to winter temperatures. The objective of this study was to evaluate the potential impacts of postharvest organic N fertilizer applications on ‘Duke’, an early fruiting northern highbush blueberry cultivar. Specific objectives were to determine the effects of postharvest organic N fertilizer application on plant growth, yield, floral bud set, fruit quality, cold hardiness, tissue macronutrient concentrations, and select soil properties. Four treatments varying in the timing of N application were evaluated in a commercial ‘Duke’ field in eastern Washington using a single fertilizer rate of 130 kg⋅ha−1 N from 2018 to 2020. The organic fertilizer N source was a liquid fertilizer derived from digested plant materials. The experimental design was a randomized complete block design with four replications and treatments included the following: control (100% of N applied preharvest); 80/20 (80% preharvest, 20% postharvest); 70/30 (70% preharvest, 30% postharvest); and 60/40 (60% preharvest, 40% postharvest). Although the year influenced measured variables, including yield, floral bud set, fruit quality, tissue nutrients, and soil properties, few treatment effects were observed across the 3-year study. Cold hardiness was only impacted once (8 Feb. 2020), and floral buds were overall hardy to extreme minimum winter temperatures for the region. This project showed that applying postharvest organic N as a liquid fertilizer had no negative consequences on productivity metrics for an early fruiting blueberry cultivar grown in a region with an extended growing season, thus providing growers with more flexibility when timing their fertilizer applications. Results may differ for other fertilizer sources, and further monitoring of soil NO3-N accumulation should be conducted to gain a better understanding of its dynamics and the potential for risks.