Blueberry Fields Research Articles

Landscape structure and farming management interacts to modulate pollination supply and crop production in blueberries

Abstract Pollination services are affected by landscape context, farming management and pollinator community structure, all of which impact flower visitation rates, pollen deposition and final production. We studied these processes in Argentina for highbush blueberry crops, which depend on pollinators to produce marketable yields. We studied how land cover and honeybee stocking influence the abundance of wild and managed pollinators in blueberry crops, using structural equation modelling to disentangle the cascading effects through which pollinators contribute to blueberry fruit number, size, nutritional content and overall yield. All pollinator functional groups responded to landscape changes at a spatial scale under 1000 m, and the significance or direction of the effects were modulated by the field‐level deployment of honeybee hives. Fruit diameter increased with pollen deposited, but decreased with honeybee abundance, which, had indirect effects on fruit acidity. Honeybees had a positive effect on the number of fruit produced by the plants and also benefited the overall yield (kg plant−1) through independent effects on both the quality and quantity components of fruit production. Synthesis and applications. Deployment of beehives in blueberry fields can buffer, but not compensate for the negative effects on honeybee abundance produced by surrounding large scale none‐flowering crops. Such compensation would require high‐quality beehives by monitoring their health and strength. The contribution of honeybees to crop production is not equal across production metrics. That is, higher abundance of honeybees increases the number of berries produced but at the cost of smaller and more acidic fruits, potentially reducing their market value. Growers must consider this trade‐off between fruit quantity and quality when actively managing honeybee abundance.

Characterization and modification of biochar from a combined heat and power (CHP) plant for amending sandy soils collected from wild blueberry fields

Wild (or lowbush) blueberries (Vaccinium angustifolium Ait.) undergo severe drought impacts due to climate warming because they grow in sandy soils with poor water retention. The feasibility was studied for using biochar in a forest biomass-fueled combined heat and power (CHP) plant to amend the sandy soils. The chemico-physical properties (e.g., bulk density, moisture content, porosity, pH) of the biochar were measured. An acid treatment method (1% to 3% acidic or citric acid solution) was developed to decrease the biochar pH from 11.4 to neutral or lower, aiming to aid in weed control in wild blueberry fields. The water holding capacity (WHC) of sandy soils (S) mixed with biochar (B) (Type I) and sandy soils mixed with both biochar and fertilizer (Type II) at four ratios of 100S:0B (control), 50S:50B, 30S:70B, and 10S:90B were measured. The biochar generated from the CHP plant had comparable physical properties (such as bulk density, porosity, pH, and surface area) with woody biochar made from pyrolysis. The acid treatment method significantly lowered the pH to a range of 5.0 to 6.5. The 50:50 mixing ratio for both Type I and Type II increased the water holding capacity by about 20% compared with control groups.

Phenotype, phenology, and disease pressure assessments in wild blueberry fields through the use of remote sensing technologies

Phenotype, phenology, and disease pressure assessments in wild blueberry fields through the use of remote sensing technologies

Erythritol sprays reduce D. suzukii infestation without impacting honey bee visitation nor fruit quality.

Spotted-wing drosophila, Drosophila suzukii, is an economic pest of small fruits and cherries. Insecticides primarily control this pest while alternative controls are in development. Laboratory studies show that erythritol is insecticidal to D. suzukii and other pests while safe for human consumption. Moreover, erythritol combined with sucrose or non-caloric sucralose can stimulate feeding and quicken mortality. Before growers can use erythritol, the impact on crop protection, non-target insects, and fruit quality need evaluation. In three blueberry and cherry field cage trials, oviposition on fruit sprayed with erythritol:sucrose or erythritol:sucralose formulations was lowered by 59-81% compared to unsprayed controls. Fly infestation (larval or adult counts from fruit) was 90% lower in a greenhouse blueberry trial, and 49% lower in an open field blueberry trial with 2M erythritol: 0.5M sucrose. Infestation was also 57% lower in an open field cherry trial with 1.5M erythritol: 0.5M sucrose. Other field trials with very low pest pressure or frequent rains revealed no differences from controls. Field trials consistently revealed that honey bees did not preferentially visit plants sprayed with either erythritol formulation, although yellow jackets visited erythritol:sucrose-sprayed plants more frequently. Erythritol formulations consistently led to more leaf spotting, but there was no reduction in quality of treated blueberries or cherries in terms of mold development, firmness, diameter, epidermal penetration force, and Brix° (total soluble solids; TSS) at harvest. Eleven trials conducted over four years show that erythritol formulations can reduce D. suzukii pressure without attracting foraging honey bees nor negatively impacting fruit quality. This article is protected by copyright. All rights reserved.

First report of Diaporthe sojae causing stem canker on blueberry in China.

Blueberry (Vaccinium corymbosum) plants are popular all over the world due to their high nutritional value and health benefits. In October 2020, blueberry stems (cv. O'Neal) displaying reddish brown necrotic lesions were observed from a blueberry field in Anqing (Anhui, China), with the incidence of approximately 90%. The affected plants were somewhat stunted that had smaller fruit, and in severe cases, partial or whole plant died. We randomly selected three sampling sites to collect stems with the symptoms. Samples at the margin between diseased and healthy tissues were taken out, cut into 5 mm pieces in length，and then mixed them together. Twenty small samples were surface-sterilized, and plated onto potato dextrose agar (PDA). The plates were incubated at 25°C in the dark until fungal colonies were observed. After subculturing single hyphal tips, 9 out of 12 fungal isolates with similar morphologies were obtained. The representative isolate, LMKY12 was selected for further identification. The colonies on PDA showed white, fluffy aerial mycelia with 7.9  0.2 mm (n=5) diameter after inoculation in darkness at 25°C for one week. The colony darkens in color with age, yellowish pigmentation in reverse were observed. After 15 days of incubation, dark brown, irregular hard particles (fruiting bodies in sexual stage) accumulated on the surface of the colonies. Asci were 8-spored, sessile, club-like, hyaline, and 35-46 x 6-9 μm (n=30) in size. The ascospores were oval or spindle shaped, two-celled, constricted at division, and containing four guttulates with larger guttules at centre and smaller one at ends, measured 9-11 x 2-4 um (n=50). No sporulation observed on blueberry stems after inoculated 30 days. In order to induce the production of conidiophores, mycelial plugs were placed on blueberry leaves and cultured in darkness at 25°C. There are two types of conidia observed after 20 days of inoculation. Alpha conidia were aseptate, hyaline, smooth, ovate to ellipsoidal, often biguttulate, measured 5.33-7.26 x 1.65-2.53 μm (n=50). Beta conidia were hyaline, linear, measured 12.60-17.91 x 0.81-1.38 μm (n=30). The morphological characteristics matched the previous description of D. sojae (Udayanga et al. 2015; Guo et al. 2020). To confirm the identification, the mycelial genomic DNA of LMKY12 was extracted as a template. The rDNA internal transcribed spacer (ITS), translation elongation factor 1-α gene (TEF1-α), and calmodulin (CAL) were amplified and sequenced using primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R, and CAL-228F/CAL-737R (Carbone and Kohn 1999), respectively. BLAST analysis revealed that the ITS (ON545758), CAL (OP886852), and TEF1-α (OP886853) sequences were 100% (527/527 base pairs), 99.21% (504/508 base pairs), and 99.41% (336/338 base pairs) similar to the strain FAU636 of D. sojae (KJ590718, KJ612115, KJ590761), respectively. Phylogenetic analysis based on concatenated sequences of ITS, TEF1-α, and CAL using MEGA 7.0 by maximum likelihood attributed the isolate LMKY12 to the D. sojae clade. Pathogenicity tests were performed on blueberry cv. O'Neal using detached stems (n=8) in laboratory, one-year-old potted plants (n=4) in greenhouse. Inoculations were done by placing mycelial plugs (7 mm in diameter) taken from a 7-day-old PDA culture on wounded stems. Inoculations with uncolonized agar plugs served as negative controls. Reddish dark brown lesions similar to the symptoms were observed on all inoculated stems 7 days after inoculation. No symptoms developed on control stems. Reisolations were successfully made from all the inoculated stems, and the pathogen was confirmed by the presence of pycnidia, alpha conidia and beta conidia. To our knowledge, this is the first report of D. sojae causing blueberry stem canker in China.

Identity and diversity of pollens collected by two managed bee species while in blueberry fields for pollination.

The nutritional needs and foraging behavior of managed bees often lead to pollen collection from flowers other than the focal crop during crop pollination. To understand the pollen needs and preferences of managed bees during blueberry pollination, we identified pollen collected by Apis mellifera Linnaeus, 1758 (Hymenoptera: Apidae) and Bombus impatiens Cresson, 1863 (Hymenoptera: Apidae) colonies across two years. Bumble bees collected a wider diversity of pollens compared to honey bees, whereas honey bees were more focused on abundant resources. Despite blueberries being the most abundant resource in the landscape, it was not the most collected pollen by either bee species in 2018. However, it was the most collected pollen by bumble bees in 2019 and they collected substantially more blueberry pollen than honey bees in both years. In 2018, buckthorn, Rhamnus L. (Rosales: Rhamnaceae) or Frangula Mill. (Rosales: Rhamnaceae), and willow, Salix L. (Malpighiales: Salicaceae), pollens were abundantly collected by both bee species. In 2019, cherry, Prunus L. (Rosales: Rosaceae), and willow (Salix) pollens were collected at high proportions by both species. Brambles, Rubus L. (Rosales: Rosaceae), and white clover, Trifolium repens L. (Fabales: Fabaceae), were also common pollen sources for honey bees, whereas oak, Quercus L. (Fagales: Fagaceae), was collected by bumble bees. Landscape analyses also revealed that certain land cover types were positively correlated with the collection of preferred pollen types. Herbaceous wetlands were associated with collection of buckthorn (Rhamnus/Frangula), willow (Salix), and cherry (Prunus) pollen, which were primary pollen resources for both bee species. There was no correlation between landscape diversity and pollen diversity, suggesting that colonies forage based on nutritional requirements rather than resource availability.

The contrasting role of climate variation on the population dynamics of a native and an invasive insect pest.

Since 2008, spotted-wing drosophila, Drosophila suzukii, has become a major pest of soft, thin-skinned fruits in the USA, causing significant annual yield losses. Historically, the native blueberry maggot fly, Rhagoletis mendax, has been a key blueberry pest in eastern North America and a driver of insecticide usage. After its invasion in 2011 into New Jersey (USA), D. suzukii has supplanted R. mendax as the main target of insecticide applications in the state. However, the impact of D. suzukii on the native R. mendax has not been documented, particularly in relation to local climate. Historical monitoring data from New Jersey blueberry farms were used to assess the role of climate on R. mendax and D. suzukii populations. Seasonal trap captures of R. mendax adults have decreased after D. suzukii invasion, while D. suzukii trap captures have increased. Similarly, D. suzukii first captures have occurred earlier each year, while R. mendax has been captured later in the growing season. Winter freezing and summer growing degree days were found to significantly correlate with D. suzukii activity. Using downscaled climate simulations, we projected that D. suzukii will arrive in New Jersey blueberry fields up to 5 days earlier on average by 2030 and 2 weeks earlier by 2050 with warming temperatures, exacerbating yield losses and insecticide usage. As regional temperatures are projected to warm and the invasive range continues to expand, we predict the rate of phenological development of the invasive D. suzukii and its impact on native insects to change noticeably, bringing new challenges for pest management strategies.

Large Remaining Forest Habitat Patches Help Preserve Wild Bee Diversity in Cultivated Blueberry Bush

Global declines in wild and managed bee populations represent a major concern for the agricultural industry. Such declines result, in part, from the loss of natural and semi-natural habitats in and around agricultural ecosystems. However, remaining forest patches in heavily modified landscapes represent nesting habitats that may be crucial to preserving wild bees and their services. Because wild bees are the main pollinators of fruit crops, preserving potential nesting habitats might be particularly important for the crops’ yield and profitability. Here, we assessed whether the abundance and richness of visiting wild bees in blueberry crops relates to the amount of surrounding forest cover and if so, whether those relationships varied with spatial scale. Specifically, we sampled wild bee communities in 18 blueberry fields during the blooming period in Montérégie, Quebec, Canada, where sampling consisted of pan trap triplets and direct observation of flower visitors on blueberry bushes. Then, we quantified the proportion of forest in radii of 0.5 km, 1 km, and 2 km around each field. Wild bee abundance was positively related to the proportion of forest habitat surrounding the crop field, but the relationship for wild bee richness was less clear. Moreover, these relationships were strongest at 1 and 2 km radii of measured land cover. Overall, pollinator diversity was highest when at least 30% of the surrounding landscape consisted of forest patches, representing a total area of at least 1 km2. Our results suggest that preserving large habitat patches in agricultural landscapes can help prevent further decline in wild bee diversity while maximizing pollination services to fruit crops.

Spatial dependency and independency of nitrogen in lowbush blueberry commercial fields

Rhizomes of wild lowbush blueberry ( Vaccinium angustifolium Aiton) extend horizontally, creating spatial dependency when fertilization trials are performed. Knowing this spatial dependency would help researchers to better design field studies. Here, we used labelled nitrogen (N) fertilizer (15N-(NH4)2SO4) to measure N translocation among blueberry stems for one old (56 year) and one younger (15 year) commercial field. Leaf 15N concentrations at the tip-dieback stage were used to monitor N acquisition. No difference between sites suggests no field age effect on N translocation. Spatial dependency and independency were reached for distances of ≤0.75 and ≥1.75 m from the fertilizer application point, respectively.

Evaluation of the Effectiveness of Loose and Compressed Wood Chip Mulch in Field-Grown Blueberries—A Preliminary Study

Blueberry production in the field faces several challenges, including competition from weeds and soil suitability. Different mulch types are widely used in blueberry cultivation to control weeds, conserve moisture, and mitigate soil erosion. However, the comparative effects of loose and compressed wood chips on fruit quality and weed control in blueberry production systems have not been studied. Many farmers use expensive imported peat moss as soil covers, while others apply organic mulches such as chips or chaff, which can be easily washed away by runoff. This study aimed to evaluate the effects of compressed mulching boards (MB) fabricated without the use of chemical adhesives using pressurized steam and compression technologies in blueberry cultivation. During the two growing seasons, the effectiveness of compressed MB on soil moisture retention, fruit quality, and weed biomass was compared to that of wood chip (WC) and control treatments in a blueberry field. Although a significant difference was observed in the fruit fresh weight, no significant differences were observed in the other fruit growth parameters for all the treatments. Generally, the compressed MB significantly improved soil moisture retention capacity compared to WC and control during the two-year study. The compressed MB showed effective weed suppression ability by significantly reducing the weed biomass at all sampling times.

Models for Apothecial Emergence and Ascospore Discharge of Monilinia vaccinii-corymbosi in Michigan Blueberry Fields

Monilinia vaccinii-corymbosi ( Mvc) is the causal agent of mummy berry in highbush blueberries. The primary inoculum of Mvc consists of ascospores that are discharged from apothecia on overwintered mummified blueberry fruits on the ground below blueberry bushes. Models currently exist in southern climates to predict the emergence of apothecia and ascospore discharge based on growing degree days. To better understand the release of primary inoculum in northern climates, apothecial emergence and ascospore discharge were studied in relation to weather variables. A Burkard spore trap was used to collect ascospores in blueberry fields with a history of the disease in 2002, 2003, 2004, and 2009. Peak ascospore discharge was inversely correlated with daily relative humidity, and the majority of ascospores were initially discharged between 61 and 291 growing degree days (using 5.5°C base) and after 1,549 to 1,924 chill hours (above freezing) were attained. The chilling requirement of pseudosclerotia was studied by removing them at different times during the winter and allowing them to germinate in the laboratory. Additionally, the optimal average apothecial cup diameter in the field was investigated in relation to ascospore discharge (between 3 and 7 mm). Finally, we proposed a simplified degree-day model to predict apothecia emergence and ascospore discharge with apothecia emergence timings at several locations from 2007 to 2010. This information can be used to predict mummy berry apothecium emergence and ascospore discharge and could be incorporated into web-based risk modeling applications for providing growers with useful tools to improve fungicide spray timing.

Wild host fruit–niche diversity of Drosophila suzukii in lowbush blueberry agroecosystems in Saguenay-Lac-Saint-Jean, Québec, Canada

Abstract Understanding movements of Drosophila suzukii (Diptera: Drosophilidae) into berry fruit crops from wild-fruit hosts in borders of semi-natural agroecosystems, such as lowbush blueberry, is important to determining harvesting time and managing wild-fruit diversity near crops. This study aimed to inventory the wild-fruit hosts associated with lowbush blueberry (Ericaceae) production in Québec, Canada, near the limits of lowbush blueberry’s eastern North American range. We also tested the hypothesis that fruit traits of berry fruit species present in or near lowbush blueberry fields might explain field infestation levels. Flies of both sexes emerged from five wild-fruit species in 2016, to which six more species were added in 2017. The most productive wild-fruit hosts were Cornus canadensis (Cornaceae) and Aralia hispida (Araliaceae) (> 100 emerged flies/100 g of fruit) in 2016, to which Prunus pensylvanica (Rosaceae) and Rubus idaeus (Rosaceae) were added in 2017. Among nine variables considered in statistical modelling (fruit size, sugar content, and reflected colour bands) and taxonomic family (a nominal variable), none could explain field infestation levels over two years. In lab tests comparing fruits of Cornus canadensis, a common weed within fields, and lowbush blueberries, mated D. suzukii females laid twice as many eggs on blueberries, but both species were equally suitable for development.

Phenological assessment of the wild blueberry field using an unmanned aerial vehicle

Phenological assessment of the wild blueberry field using an unmanned aerial vehicle

Machine vision system for real-time debris detection on mechanical wild blueberry harvesters

Improving fruit quality is important to wild blueberry producers. Plant debris like leaves and stems caused a reduction in fruit quality during mechanical harvesting. A debris detection system was developed using two Logitech C920 webcam cameras mounted before and after the blower fan on a commercial mechanical wild blueberry harvester. Images were collected from two commercially managed wild blueberry fields located in central Nova Scotia to develop a dataset of 1000 images. Two convolutional neural networks (CNNs), YOLOv3 and YOLOv3-SPP, were used and compared for performance analysis. The CNNs were trained using no augmented images, images with five augmentations (sharpening, brightness, contrast, gamma correction, and saturation), and images with five augmentations that were more heavily weighted towards gamma. Four different computer hardware packages (Hewlett-Packard, Shuttle XPC, Jetson TX2, and GPU-based Desktop) were used to determine the appropriate hardware and CNN model combination for real-time performance. YOLOv3 and YOLOv3-SPP were trained to mAP scores of 72.87 and 74.38% using the dataset with more gamma-augmented images. This was an improvement over the dataset with no augmentation (67.75; 68.49%) and equally numbered augmentations (71.26%; 73.03%). YOLOv3-SPP combined with an Intel® Core™ i9-7900X CPU and Nvidia GeForce RTX™ 2080 Ti GPU in a desktop computer achieved the fastest detection rate of 33.30 ms. The detection speed on all other hardware configurations exceeded 33.30 ms, indicating that a powerful desktop GPU is required for real-time performance of this task. With adequate processing hardware, the developed technology could be integrated into a control system to automatically adjust brushes based on conveyor information from mechanical wild blueberry harvesters to make cleaning berries easier and enhance fruit quality.

Evaluation of acetolactate synthase (ALS)-inhibiting herbicides for red sorrel (Rumex acetosellaL.) management in lowbush blueberry (Vaccinium angustifoliumAiton)

Red sorrel is a common herbaceous perennial weed species in lowbush blueberry fields that may be managed with acetolactate synthase (ALS)-inhibiting herbicides. Greenhouse and field experiments were established to determine the crop tolerance and potential efficacy on red sorrel of tribenuron-methyl, nicosulfuron + rimsulfuron, foramsulfuron, flazasulfuron, pyroxsulam, and halosulfuron-methyl. Ramet density of greenhouse-grown red sorrel plants established from root fragments was reduced by tribenuron-methyl, flazasulfuron, and pyroxsulam, though tribenuron-methyl and flazasulfuron were the most consistently effective herbicides under field conditions. Spring non-bearing year tribenuron-methyl and flazasulfuron applications reduced both non-bearing and bearing year total red sorrel ramet density and reduced non-bearing year red sorrel flowering ramet and seedling density without injuring lowbush blueberry. Fall non-bearing year tribenuron-methyl and flazasulfuron applications reduced bearing year red sorrel total and flowering ramet density, and this application timing should be evaluated further to improve understanding of crop injury risks. Fall bearing year tribenuron-methyl and flazasulfuron applications reduced non-bearing year red sorrel total and flowering ramet density but did not reduce seedling density. Nicosulfuron + rimsulfuron, foramsulfuron, pyroxsulam, and halosulfuron-methyl efficacy on red sorrel were inconsistent or limited, and these herbicides are not recommended for red sorrel management in lowbush blueberry.

Honey Bee Exposure to the Fungicide Propiconazole in Lowbush Blueberry Fields

The fungicide propiconazole is a commonly used fungicide in small fruit and tree fruit production in the U.S.A. In Maine wild blueberry production, it is used almost exclusively for mummy berry disease control. The goal of this study is to assess the risk of exposure to honey bee colonies deployed in wild blueberry fields for pollination. The study was conducted over a six-year period (2009–2014) in both the field and laboratory. Field surveys (2009–2011) measured the residues on blueberry flowers in 41 commercial fields across the blueberry growing region. A two-year study (2010–2011) determined the decay rate of propiconazole in blueberry fields after application. A laboratory study determined the contact LD50 of propiconazole to honey bee workers (2013). A field exposure/effect study was conducted over three years (2011–2013). In this study, 8–18 previously unexposed colonies were randomly assigned to one of two treatments, (1) isolated fields that were treated prior to bloom with the fungicide, propiconazole, but no other pesticides, or (2) isolated fields that were not treated with propiconazole or any other pesticides. The measures taken to evaluate effects of exposure monitored each year were (1) estimation of the exposure to colonies, measured as residues on flowers, workers, and in pollen brought back to hives; (2) colony population size (workers and brood); (3) queen status and presence; (4) queen oviposition rate; (5) supersedure rate; (6) egg hatch success; (7) mortality of developing larvae and pupae; (8) royal jelly deposition in wax comb cells; (9) worker longevity; (10) foraging activity; (11) treated bloom repellency to foragers; (12) colony overwintering success; (13) worker hypopharyngeal gland acini size; and (14) pathogen and parasite incidence and intensity. The results of these experiments and surveys showed that the propiconazole contact LD50 was 24,747 ppb. Residues of propiconazole were found to be commonly abundant on flowers in treated commercial fields after application with a mean concentration of 2083.8 ± 851.3 (se). The decay of propiconazole to non-detectable levels took about 40 days after application. The three-year hive deployment study showed that residues in treated fields were detected on flowers, pollen, and worker bees, demonstrating that exposure to this fungicide occurs even though it is applied before bloom. Also in the hive deployment study, evidence of reduced colony populations, increased supersedure, decreased queen oviposition rate, increased pathogen or parasite incidence and intensity, and increased overwintering colony loss due to propiconazole exposure was not found. However, propiconazole exposed colonies exhibited reduced worker longevity (17.3%), hypertrophy of 5 d old nurse bee hypopharyngeal acini (8.3%), and a 3.5 h repellency of foragers to treated bloom.

Landscape-level honey bee hive density, instead of field-level hive density, enhances honey bee visitation in blueberry

ContextTo date, managing honey bees and wild bees within crop fields remains challenging. Landscape structure is often overlooked when studying the pollination contribution of honey bees. Increasing our understanding on how to predict honey bee visitation in crops is crucial for sustainable management of agroecosystems.ObjectivesWith this study we investigated which landscape and field-level variables determine honey bee and wild bee visitation, and whether honey bee or wild bee visitation influence crop pollination.MethodsSixteen highbush blueberry fields were surveyed for honey bees, wild bees, and crop pollination in Washington, USA. Additionally, within a radius of 1000 m around each field all honey bee hives were located and the surrounding landscape was characterized.ResultsHoney bee hive numbers in the landscape positively correlate with the proportion of blueberry in the landscape. Honey bee visitation was best predicted by landscape-level hive density within a radius of 1000 m, whereas semi-natural habitat and field-level hive density did not impact honey bee visitation. The amount of semi-natural habitat and blueberry within a radius of 1000 m had a positive and negative impact, respectively, on wild bee visitation. Honey bee visitation had a positive effect on blueberry seed set.ConclusionWe conclude that honey bee visitation is determined by the number of honey bee hives in the surrounding landscape. Hence, field-level hive density recommendations miss contributions from other hives in the landscape. Furthermore, semi-natural habitat did not impact honey bee visitation and contributes to diversifying pollinator diets and provides wild bee habitat.

Proximal and Remote Sensing Data Integration to Assess Spatial Soil Heterogeneity in Wild Blueberry Fields

Wild blueberries (Vaccinium angustifolium Ait.) are often cultivated uniformly despite significant within-field variations in topography and crop density. This study was conducted to relate apparent soil electrical conductivity (ECa), topographic attributes, and multi-spectral satellite imagery to fruit yield and soil attributes and evaluate the potential of site-specific management (SSM) of nutrients. Elevation and ECa at multiple depths were collected from two experimental fields (referred as FieldUnd, FieldFlat) in Normandin, Quebec, Canada. Soil samples were collected at two depths (0–0.05 m and 0.05–0.15 m) and analyzed for a range of soil properties. Statistical analyses of fruit yield, soil, and sensor data were used to characterize within-field variability. Fruit yield showed large variability in both fields (CVUnd = 54.4%, CVFlat = 56.5%), but no spatial dependence. However, several soil attributes showed considerable variability and moderate to strong spatial dependence. Elevation and the shallowest depths of both the Veris (0.3 m) and DUALEM (0.54 m) ECa sensors showed moderate to strong spatial dependence and correlated significantly to most soil properties in both study sites, indicating the feasibility of SSM. In place of management zone delineation, a quadrant analysis of the shallowest ECa depth vs. elevation provided four sensor combinations (scenarios) for theoretical field conditions. ANOVA and Tukey–Kramer’s post hoc test showed that the greatest differentiation of soil properties in both fields occurred between the combinations of high ECa/low elevation versus low ECa/high elevation. Vegetation indices (VIs) obtained from satellite data showed promise as a biomass indicator, and bare spots classified with satellite imagery in FieldUnd revealed significantly distinct soil properties. Combining proximal and multispectral data predicted within-field variations of yield-determining soil properties and offered three theoretical scenarios (high ECa/low elevation; low ECa/high elevation; bare spots) on which to base SSM. Future studies should investigate crop response to fertilization between the identified scenarios.

Influence of Fertigation and Granular Applications of Potassium Fertilizer on Soil pH and Availability of Potassium and Other Nutrients in a Mature Planting of Northern Highbush Blueberry

Although northern highbush blueberry (Vaccinium corymbosum L.) fields are often fertigated using soluble or liquid fertilizers, recommendations for applying most nutrients to the crop, including K, are based on the use of granular fertilizers. The objective of the present study was to compare fertigation to granular application of K in a mature planting of Duke, a popular early season blueberry cultivar that ripens from June through July in Oregon and Washington. The plants were grown on raised beds and irrigated using two lines of drip tubing per row. Treatments were initiated in 2016 and included no K fertilizer, a single application of granular potassium sulfate (K2SO4) in April, and fertigation once a week from April to August with soluble K2SO4 or liquid potassium thiosulfate (K2S2O3). Each treatment was applied for 2 years at a total rate of 70 kg·ha−1 K per year. The plants were also fertigated with 168 and 224 kg·ha−1 N in 2016 and 2017, respectively, and 30 kg·ha−1 P per year. Although extractable soil K was initially low at the site (144 mg·kg−1), the treatments had no effect on plant dry weight, yield, fruit quality, or the concentration of K in recently expanded leaves. However, during the first year of the study, K fertigation with K2SO4 or K2S2O3 reduced soil pH and increased the concentrations of K+, Ca2+, Mn2+, and SO42− in the soil solution under the drip emitters compared with no K or granular K2SO4, whereas granular application of K2SO4 resulted in higher concentrations of K+ between the emitters than any other treatment. Fertigation also affected the concentration of K in the fruit during the first year, although in this case, the concentration was lower with K fertigation than with no K or granular applications of K2SO4. During the second year, fertigation and granular K continued to result in higher concentrations of K+ in soil solution under and between the drip emitters, respectively, but at this point, extractable soil K was higher with each of the K fertilizers than with no K. Consequently, the concentration of K in leaves sampled from entire plants in late September that year was higher with any of the K fertilizers than with no K. Potassium fertilization also altered concentrations of other nutrients in the plants, including Mg, S, B, Cu, and Mn in the leaves; Ca, Mg, and B in the fruit; Mn and Zn in the woody canes; and P, Mg, S, and Mn in the crown. In many cases, concentrations of these nutrients were higher with one or more of the K fertilizers than with no K. Thus, regardless of the application method, K2SO4 and K2S2O3 appear to be good sources for increasing availability of K and other nutrients in the plants and soil. However, the amount of K in the plants was sufficient at the site, and therefore, none of the fertilizers provided a short-term benefit to growth or fruit production in the present study.

Contrasting effects of landscape on nest founding and colony success of bumble bees in a mixed‐crop agroecosystem

Abstract Nest‐founding bumble bee queens search landscapes broadly for a nest site, whose later‐developed workers are constrained to foraging around the nest. Landscape could therefore have different influences on nest site selection and subsequent colony success. Additionally, the density of bumble bees in a landscape reflects the product of their nest density and nest success. To examine separate landscape effects on nest density and success, we examined nest occupancy (reflecting nest density) and colony size (reflecting nest success) using ground‐installed nest boxes placed adjacent to blueberry (Vaccinium corymbosum) fields in the Lower Mainland of British Columbia, Canada. Nest‐searching queens occupied 59% of these boxes. We classified landscapes in a 1.5 km radius of colonies using habitats of a priori relevance to bumble bees: beneficial (i.e. flowering) agriculture, non‐beneficial agriculture (NBA), forest, open semi‐natural, suburban, and their configuration (habitat edge density). Landscape strongly affected nest founding but only weakly affected colony success. Nest founding increased in landscapes with more forest habitat, more open semi‐natural habitat (and little NBA), and more habitat edge (and little NBA). Colony success increased in landscapes with more edge density (and much NBA). Overall, edge habitats enhanced bumble bee populations, but enhancement was conditional: edge increased nest occupation in landscapes with little NBA and nest success in landscapes with a lot of NBA. Populations of crop‐pollinating bumble bees might therefore best be enhanced by locally enhancing nesting: protecting forests, 2D semi‐natural habitats (when flowering crops are uncommon), and edge habitats.