Foliar Applications of Calcium and Boron Do Not Increase Fruit Set or Yield in Northern Highbush Blueberry (Vaccinium corymbosum)

Abstract

<jats:p>Fruit set in northern highbush blueberry (<jats:italic>Vaccinium corymbosum</jats:italic> L.) can be low under certain climatic conditions, contributing to reduced yields in northwestern Washington. The mechanisms influencing fruit set are complex, but reduced fruit set may be associated with inadequate nutrient availability during critical stages of flowering, ovule fertilization, and initial fruit development. Calcium (Ca) and boron (B) are of particular interest for reproductive developmental processes and are frequently applied annually by growers in the Pacific Northwest region because of the perception that these nutrients enhance fruit set and corresponding yields. Evaluation of commonly applied products containing these nutrients and their effects on fruit set and yield are of specific importance to justify the application of these nutrients. To address this, commercially available fertilizers containing Ca and B were applied to ‘Draper’ and ‘Bluecrop’ blueberry as foliar sprays, either alone or in combination, during the 2015 and 2016 growing seasons in northwestern Washington. Treatments included calcium chloride (750 and 1500 ppm Ca), calcium sulfate (150 ppm Ca), and tetra borate (125 and 250 ppm B) foliar sprays, repeated six times per season every 7–10 days from early pink bud through petal fall. No significant increases were observed for fruit set, estimated yield, and fruit quality (firmness and berry weight) across the treatments. Increased concentrations of B were observed in leaf tissues in 2015 and 2016, and to a lesser extent fruit tissues. Calcium remained unchanged regardless of treatment and tissue type. Under the conditions of this study, foliar applications of Ca and B did not lead to increased fruit set or yield. This research suggests that other approaches should be explored to increase fruit set and corresponding yields of highbush blueberry grown in northwest Washington.</jats:p>

Organic Production Systems in Northern Highbush Blueberry: II. Impact of Planting Method, Cultivar, Fertilizer, and Mulch on Leaf and Soil Nutrient Concentrations and Relationships with Yield from Planting through Maturity

“…Leaf B concentrations were below sufficiency levels the entire study period, despite sufficient or close to sufficient levels of soil B and application of additional fertilizer B as a granular to the soil and as a foliar product just before bloom according to the recommended practice (Hart et al, 2006). Although sufficient plant levels of B are thought to be critical for good pollination and fruit or seed set, frequent applications of foliar B, while improving leaf and fruit B concentrations in some cases, had no impact on fruit set or yield in Washington (Arrington and DeVetter, 2017). In our study, leaf B was not consistently related to yield.…”

“…Although Strik and Vance (2015) found considerable variation in leaf and fruit Ca concentrations, there did not appear to be a relationship in these values for either cultivar. In addition, foliar applications of Ca at manufacturer recommended rates have not been found effective to increase fruit Ca concentration (Arrington and DeVetter, 2017;Vance et al, 2017), likely due to the relatively short time that stomates are functional in blueberries and the impact on Ca uptake through the xylem (via transpiration) in the fruit (Yang, 2018). Although the use of feather meal increased fruit Ca concentration in this trial relative to fish solubles (Fernandez-Salvador, unpublished data), the relationship between leaf and fruit Ca concentrations was inconsistent with both negative and positive correlations in 'Liberty' and 'Duke', respectively, in 1 out of 2 years.…”

Highbush Blueberry Cultivars Differ in the Relationship between Seed Number and Berry Weight during the Harvest Season

“…In our study, minimum seed number also varied greatly among cultivars. In Washington, Arrington and DeVetter (2018) found fewer seeds/berry in 'Duke' (11-33) than in our study, but also reported lower fruit set in their region, likely because of adverse weather reducing pollinator activity (Arrington and DeVetter, 2017). Increased pollinator activity through stocking with more hives/ha increased seeds/berry (Arrington and DeVetter, 2018).…”

“…Cultivars differ in percent fruit set or seed set because of differing bloom periods and associated differences in weather (Arrington and DeVetter, 2017), differences in attractiveness of the flowers to pollinators (Courcelles et al, 2013), and genetic differences in self-or cross-compatibility and pollen quantity or quality (e.g., Brewer and Dobson, 1969;Chavez and Lyrene, 2009;Ehlenfeldt and Kramer, 2012;MacKenzie, 1997;Rabaey and Luby, 1988;Vander Kloet, 1983). As a result, cultivars have been found to differ in the seeds/berry and, often as a result, berry size (Arrington and DeVetter, 2018;Brewer and Dobson, 1969;DeVetter et al, 2016;Eaton, 1967;Ehlenfeldt, 2001;Ehlenfeldt and Martin, 2010;Gupton, 1984;Gupton and Spiers, 1994;Jackson et al, 1972;Lang and Danka, 1991;Lyrene, 1989;Meader, 1936;Meader andDarrow, 1944, 1947;Moore et al, 1972;Morrow, 1943;Payne et al, 1989;Taber and Olmstead, 2016).…”

Foliar Calcium Corrects a Deficiency Causing Green Fruit Drop in ‘Draper’ Highbush Blueberry (Vaccinium corymbosum L.)

“…Fall foliar Ca applications to increase the amount that is stored by the plant during the dormant season, and that will be available for remobilization in the spring, is a potential strategy for reducing GFD pre-disposition. Thus far, our initial attempts to reduce GFD by increasing plant Ca through fall foliar applications in the previous year have not been effective (data not shown), and a subsequent study by researchers in northwestern WA has shown no effect of fall Ca on GFD in the following year [71].…”