Evaluating Postharvest Organic Nitrogen Fertilizer Applications in Early Fruiting Northern Highbush Blueberry

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.

Effects of Machine-Harvest Interval on Fruit Quality of Fresh Market Northern Highbush Blueberry

Machine harvesting blueberry (Vaccinium sp.) alleviates labor costs and shortages but can reduce fruit quality. Installation of softer catching surfaces inside modified over-the-row harvesters (modified OTR) and adjusting harvest intervals may improve fruit quality and packout. The objective of this study was to determine the effect of harvest interval on fruit quality of fresh market northern highbush blueberry (Vaccinium corymbosum L.) harvested using a modified OTR. ‘Liberty’ blueberry bushes were harvested by hand or using a modified OTR at 3-, 10-, and 14-day intervals in 2019 and at 7-, 11-, and 14-day intervals in 2020. Hand-harvested ‘Liberty’ had greater packout and firmness than machine-harvested fruit. Machine harvesting at the 3-day interval in 2019, and the 14-day interval in 2020 reduced packout from 70–80% to 60% and 54%, respectively. In 2019, machine harvesting at a 3-day interval overall resulted in fruit with greater firmness, higher titratable acidity (TA), and lower total soluble solids (TSS) and SS/TA, compared to other harvest intervals. In 2020, the 7-day machine-harvest interval had a greater TA and lower TSS/TA, compared to the 11- and 14-day intervals. Overall, modified OTR machine-harvest intervals can be extended to 10–11 days for fresh market northern highbush cultivars such as ‘Liberty’ grown in northwest Washington.

Honey bee (Apis mellifera) colony strength and its effects on pollination and yield in highbush blueberries (Vaccinium corymbosum)

Many pollination studies with honey bees have examined the effect of colony density on crop yield and yet overlook the effect of variation in the population size of these colonies. High colony density in northern highbush blueberry has been met with concerns from beekeepers who feel higher densities will intensify outbreaks of European foulbrood (EFB, Melissococcus plutonius, Truper and dé Clari), a honey bee brood disease. The purpose of this study was to confirm the prevalence of EFB in colonies pollinating blueberries and to determine whether field-level variation in the population of adult workers in colonies explained variation in blueberry fruit set and/or yield. We addressed these objectives over the course of two production seasons at 13 commercial blueberry fields in Oregon, USA, stocked with identical densities of 10 colonies/ha. We confirmed that all colonies had negligible symptoms of EFB at the start of blueberry pollination, but 53% of colonies in 2019 and 41% in 2020 had symptoms immediately following the pollination season. We also validated a method for rapidly assessing adult honey bee colony populations, namely by counting the rate of foragers returning to colonies, and it was found to be strongly correlated to true internal adult bee population independent of year and ambient temperature at the time of evaluation. Using returning forager counts, we determined there was considerable variation in the average population of colonies at each field, ranging from an estimated 10,300 to 30,700 adult worker bees per colony. While average colony strength did not predict variation in fruit set, it was related to variation in yield, independent of year. Our linear model of flight count (as a proxy for colony strength) predicts estimated yield increases of up to 25,000 kg/ha of blueberries could be achieved by colonies stronger than the recommended six frame minimum, suggesting that higher pollination benefits could be achieved without increasing hive density if stronger colonies are promoted.

Phytochemical research and anti-inflammatory activity of the dry extracts from northern highbush blueberry leaves

All over the world, non-steroidal anti-inflammatory drugs (NSAIDs) are taken annually by about three hundred million people and this figure is constantly increasing. At the same time, NSAIDs are also one of the most common causes of side effects of drug therapy. The development and implementation of new anti-inflammatory drugs, including those of plant origin, with minimal side effects is an urgent task of modern pharmaceutical science. Vaccinium corymbosum L. (family Ericaceae), which is gaining more and more popularity among berry crops and is successfully cultivated in Ukraine, is promising in this direction for research. The aim: phytochemical analysis of dry extracts from blueberry leaves to establish the possibility of creating new drugs with anti-inflammatory activity. Materials and methods. The objects of the study were dry extracts of northern highbush blueberry leaves. The content of amino acids and phenolic compounds was determined by HPLC and spectrophotometry. The prototypal activity was studied in vivo and in vitro. Research results. 4 dry extracts were obtained from northern highbush blueberry leaves. In the extracts obtained by HPLC, 7 amino acids were identified, including 3 essential ones: arginine, histidine, and phenylalanine. As a result of the HPLC study, 7 phenolic compounds were identified in extracts from the leaves of northern highbush blueberry: 5 flavonoids - rutin, quercetin-3-O-glucoside, kaempferol-3-O-glucoside, quercetin and kaempferol and 2 hydroxycinnamic acids, chlorogenic and caffeic acid. For the first time, the anti-inflammatory effect of extracts from blueberry leaves was investigated. It was revealed that extract 1 at a dose of 50 mg/kg and extract 4 modified with arginine at a dose of 25 mg/kg have the highest anti-inflammatory activity. Conclusions. The results of the conducted studies indicate that extracts from the leaves of northern highbush blueberry in terms of the content of biologically active substances are promising sources for the creation of new drugs and dietary supplements with anti-inflammatory activity

An Energy Balance Model for Predicting Berry Temperature and Scheduling Sprinklers for Cooling in Northern Highbush Blueberry

Heat-related fruit damage is a prevalent issue in northern highbush blueberry (Vaccinium corymbosum L.) in various growing regions, including the northwestern United States. To help address the issue, we developed a simple climatological model to predict blueberry fruit temperatures based on local weather data and to simulate the effects of using over-canopy sprinklers for cooling the fruit. Predictions of fruit temperature on sunny days correlated strongly with the actual values (R2 = 0.91) and had a root mean-square error of ≈2 °C. Among the parameters tested, ambient air temperature and light intensity had the greatest impact on fruit temperature, whereas wind speed and fruit size had less impact, and relative humidity had no impact. Cooling efficiency was estimated successfully under different sprinkler cooling intervals by incorporating a water application factor that was calculated based on the amount of water applied and the time required for water to evaporate from the fruit surface between the intervals. The results indicate that water temperature and nozzle flow rate affected the extent to which cooling with sprinklers reduced fruit temperature. However, prolonging the runtime of the sprinklers did not guarantee lower temperatures during cooling, because cooling efficiency declined as the temperature of the fruit approached the temperature of the irrigation water. Users could incorporate the model into weather forecast programs to predict the incidence of heat damage and could use it to make cooling decisions in commercial blueberry fields.

Individual and Combined Use of Sawdust and Weed Mat Mulch in a New Planting of Northern Highbush Blueberry. III. Yield, Fruit Quality, and Costs

A 4-year trial was established in Oct. 2016 in western Oregon to evaluate the effects of various in-row mulch treatments on yield, fruit quality, and costs of installation and maintenance during establishment of northern highbush blueberry (Vaccinium corymbosum L. ‘Duke’). The treatments included douglas fir [Pseudotsuga menziesii (Mirb.) Franco] sawdust, black weed mat (woven polypropylene groundcover), green weed mat, and sawdust covered with black or green weed mat. Fruit were harvested during 2018–20 (second through fourth growing seasons). Weed mat color had no effect on yield or fruit quality. In 2018, yield was higher with black weed mat over sawdust mulch than with black weed mat alone, whereas mulch had no effects during 2019 and 2020, or on cumulative yield. Percent total soluble solids in the berries was highest with sawdust and weed mat alone compared with weed mat over sawdust mulches, whereas berry weight, diameter, and firmness were unaffected by mulch. Sawdust was the most expensive mulch over the lifespan of the planting because it required replenishment after 2 years. Black weed mat over sawdust resulted in the highest net profit when fruit sales and cost of materials and labor were considered.

Sensitivity of Northern Highbush Blueberry Cultivars to Soil Water Deficits during Various Stages of Fruit Development

In many regions, water limitations are increasing because of frequent and persistent droughts and competition for water resources. As a result, growers in these regions, including those producing blueberries, must limit irrigation during drier years. To identify the most critical periods for irrigation, we evaluated the effects of soil water deficits during various stages of fruit development on different cultivars of northern highbush blueberry (Vaccinium corymbosum L.). The study was conducted for 2 years in western Oregon and included two early season cultivars, ‘Earliblue’ and ‘Duke’, a midseason cultivar, ‘Bluecrop’, and two late-season cultivars, ‘Elliott’ and ‘Aurora’. Volumetric soil water content and stem water potentials declined within 1 to 2 weeks with no rain or irrigation in each cultivar and were lowest during the later stages of fruit development. Water deficits reduced berry weight by 10% to 15% in ‘Earliblue’ and ‘Elliott’ when irrigation was withheld in the second year during early or late stages of fruit development and by 6% to 9% in ‘Aurora’ when irrigation was withheld in either year during the final stages of fruit development. However, water deficits only reduced yield significantly in ‘Aurora’, which produced 0.8 to 0.9 kg/plant fewer fruit per year when irrigation was withheld during fruit coloring. In many cases, water deficits also reduced fruit firmness and increased the concentration of soluble solids in the berries, but they had inconsistent effects on titratable acidity and sugar-to-acid ratios. As a rule, water deficits were most detrimental during later stages of fruit development, particularly in midseason and late-season cultivars, which ripened in July and August during the warmest and driest months of the year.