Blueberry Crop Research Articles

Short communication: Laboratory evaluation of nine highbush blueberry cultivars susceptibility to Drosophila suzukii (Matsumura, 1931) in the Southwestern Spain

Aim of study: To determine how susceptible the most used Southern highbush blueberry (SHB) cultivars were to the spotted wing Drosophila (SWD), Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae) as well as those recently introduced to Southwestern Spain.Area of study: Southwestern Spain (Huelva province).Material and methods: Nine of the SHB cultivars which were recently introduced in Southwestern Spain and the most used ones were selected: ‘Arana’, ‘Camellia’, ‘Kirra’, ‘Mayra’, ‘Misty’, ‘O'Neal’, ‘Sharpblue’, ‘Star’ and ‘Ventura’. In order to determine how susceptible the cultivars were to SWD, no-choice tests were performed under laboratory conditions. In addition, berry size, berry firmness, ºBrix, and pH were recorded in order to assess what influence these variables had on oviposition preference by SWD.Main results: Mean clutch size and mean number of emerged adults in ‘Star’ were significantly higher than in the other tested cultivars. ‘Mayra’, ‘Camellia’ and ‘Ventura’ received the lower clutch sizes and mean number of emerged adults. Mean developmental time (egg to adult) differed significantly among tested cultivars and were highest in ‘Camellia’ than in the other tested cultivars. Only firmness and pH were correlated with SWD infestation as females tend to oviposit more eggs in softer fruits than in firmer fruits. Results also showed that a higher pH increased the emergence of adults and shortened the egg to adult developmental time.Research highlights: Our results showed significant differences in the susceptibility of SHB to SWD. This information may help design IPM programs and in making recommendations for blueberry crops as planting of low-chill cultivars expands.

Deterrent Effects of Essential Oils on Spotted-Wing Drosophila (Drosophila suzukii): Implications for Organic Management in Berry Crops.

Simple SummarySpotted-wing drosophila (Drosophila suzukii Matsumura; SWD) poses a significant threat to small fruit production world-wide. Though frequent applications of insecticides is the dominant strategy to manage this pest, insecticide resistance is a concern. Resistance has already been reported for one of the only consistently effective insecticides labeled for organic production systems, spinosad, underscoring the need to diversify management strategies. Botanical products, such as essential oils, contain volatile organic compounds (VOCs) which could interfere with SWD preference for or ability to locate host fruit. We conducted laboratory and field studies to determine the efficacy of botanical products (lavender oil, catnip oil, KeyPlex Ecotrol® PLUS, and KeyPlex Sporan® EC2) on preventing SWD infestation in raspberry and blueberry crops. Under laboratory conditions lavender oil, Ecotrol, and Sporan deterred SWD from diet. In the field trials, Ecotrol deterred SWD from raspberries; however, no differences were seen in blueberry infestation. To optimize essential oil deterrents for SWD, such as how to maintain effective concentrations for longer periods of time, further research is needed. Botanical deterrents represent a promising alternative pest management strategy that could be implemented without additional equipment investment from growers, while decreasing the use of broad-spectrum insecticides.Due to concerns about frequent applications of spinosad and other broad spectrum insecticides for managing spotted-wing drosophila (Drosophila suzukii Matsumura, SWD), we investigated the use of essential oils as an alternative to current insecticides. Essential oils from a number of plant species have been studied for their attraction and deterrence of SWD. However, these botanical products have not been thoroughly tested in the field. We conducted laboratory and field studies to determine the efficacy of botanical products, including lavender (Lavandula angustifolia Mill.) oil, catnip (Nepeta cataria L.) oil, KeyPlex Ecotrol® PLUS, and KeyPlex Sporan® EC2 on preventing SWD infestation in raspberry (Rubus idaeus L.) and blueberry (Vaccinium corymbosum L.) crops. In a two-choice laboratory bioassay, lavender oil, Ecotrol, and Sporan treatments deterred SWD from a yeast-cornmeal-sugar based fly diet. In the field trials, raspberry fruit treated with Ecotrol had lower SWD infestation (6%), compared to the control (17%), and was comparable to spinosad (6%). No differences were seen in blueberry infestation. The combination of essential oils in Ecotrol may work to decrease SWD fruit infestation under certain conditions in the field, however more research is needed on the longevity of these products.

Diversity and nutritional value of pollen harvested by honey bee (Hymenoptera: Apidae) colonies during lowbush blueberry and cranberry (Ericaceae) pollination

AbstractThe growth of the commercial pollination industry raises important concerns regarding honey bee (Apis mellifera Linnaeus; Hymenoptera: Apidae) health and development. While providing such services, honey bees are often exposed to undiversified pollen sources that may contribute to nutritional deficiencies, notably in protein and amino acids. To understand how honey bees are affected during provision of pollination services, we compared honey bee colonies that pollinated lowbush blueberry (Vaccinium angustifolium Aiton; Ericaceae) and/or cranberry (Vaccinium macrocarpon Aiton; Ericaceae) crops (management strategies) with control colonies in a diversified farmland environment. We identified the floral species of pollen collected by honey bee colonies in those crops compared to pollen collected by control colonies. We also analysed the protein and essential amino acid content of collected pollen and bee bread and measured the nutritional impact of pollination services on honey bee colonies. We found that honey bees providing blueberry and/or cranberry pollination services are exposed to a less diversified pollen diet than colonies located in a farmland environment, especially in a cranberry field. There was a significantly lower proportion of crude protein content in collected and stored pollen during provision of blueberry pollination services, which led to a smaller brood population. Many nutritional deficiencies were measured with regards to essential amino acids.

Image recognition of Legacy blueberries in a Chilean smart farm through deep learning

Agriculture is one of the most important pillars of development in Chile. However, it is expected that around the year 2030 there is going to be a gradual decrease in the number of farmers. Therefore, it is necessary to replace this workforce with technology and mechanization. One way to do this is through smart farms to leverage agricultural production. The contribution of this research work is a novel approach for deep-learning image recognition of Legacy blueberries in the rooting stage that can be used in smart farms in Chile. Legacy blueberry is a variety of Southern Highbush blueberry. This species constitutes 80% of the blueberry crops in Chile. Specifically, we propose an image recognition approach based on a convolutional neural network (CNN) to detect the presence of trays with living blueberry plants, the presence of trays without living plants, and the absence of trays. The average results of the evaluation of the predictive model are as follows: accuracy: 86%, precision: 86%, recall: 88%, and F1 score: 86%.

DYNAMICS OF SOIL NUTRIENT STATUS OF HIGHBUSH BLUEBERRY IN LATVIA, 2006-2017

In Latvia, the first commercial highbush blueberry (Vaccinium corymbosum L.) plantings have been established on a few hectares at the end of the 1990th. Since then, a remarkable growth has noticed and today the total cultivated area reaches 280 hectares. An increasing market demand for fresh and processed berries provides a future upward trend in the development of blueberry crop in Latvia. In general, blueberry is a highly specialized crop that has definite soil agrochemical and climatic requirements. There are two main soil types used for blueberry cultivation in Latvia: well-drained acid sandy soils with high organic matter content and sphagnum peat soils. Evaluation and management of plant mineral nutrition in such diverse soils are based on guidelines for the particular type of growing medium. A long-term study (2006-2017, divided into three periods: 2006-2009, 2010-2013, 2014-2017) was done to find out the nutrient status of blueberry soils in Latvia. In total, 330 mineral and peat soil samples were collected from the upper layer of soils (0 - 20 cm) across blueberry plantations in Latvia and tested on plant available nutrients (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, Mo, B), as well as soil pHKCl and electrical conductivity. In general, more than 50% of blueberry soils had low content of N, S, Mo and B, as well as a high level of Mn over the study period of 2006-2017. Less than 25% of samples in the optimum range indicated on N as the most deficient nutrient.

Transcriptome analysis and annotation: SNPs identified from single copy annotated unigenes of three polyploid blueberry crops.

Blueberry is a kind of new rising popular perennial fruit with high healthful quality. It is of utmost importance to develop new blueberry varieties for different climatic zones to satisfy the demand of people in the world. Molecular marker assisted breeding is believed to be an ideal method for the development of new blueberry varieties for its shorter breeding cycle than the conventional breeding. Simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs) markers are widely used molecular tools for marker assisted breeding, which could be detected at large scale by the transcriptome sequencing. Here, we sequenced the leaves transcriptome of 19 rabbiteye (Vaccinium ashei Reade), 13 southern highbush (Vaccinium. corymbosum L × native southern Vaccinium Spp) and 22 cultivars of northern highbush blueberry (Vaccinium corymbosum L) by using next generation sequencing technologies. A total of 80.825 Gb clean data with an average of about 12.525 million reads per cultivar were obtained. We assembled 58,968, 55,973 and 53,887 unigenes by using the clean data from rabbiteye, southern highbush and northern highbush blueberry cultivars, respectively. Among these unigenes, 3599, 3495 and 3513 unigenes were detected as candidate resistance genes in three blueberry crops. Moreover, we identified more than 8756, 9020, and 9198 SSR markers from these unigenes, and 7665, 4861, 13,063 SNPs from the annotated single copy unigenes, respectively. The results will be helpful for the molecular genetics and association analysis of blueberry and the basic molecular information of pest and disease resistance of blueberry, and would also offer huge number of molecular tools for the marker assisted breeding to produce blueberry cultivars with different adaptive characteristics.

Development and field evaluation of a machine vision based in-season weed detection system for wild blueberry

The wild blueberry crop requires the heavy application of agrochemicals for the proper crop yield and weed control. An integrated machine vision based weed detection system was developed to target goldenrod weed spot-specifically. Color co-occurrence matrices and statistical classifiers were used for the goldenrod detection. The linear and quadratic classifiers were developed using different reduced sub-sets of textural features. The classifiers were evaluated using accuracy, specificity, sensitivity, and false negative ratio at Laboratory scale. Performance of the developed weed detection system was also evaluated in two wild blueberry fields. The results indicated that quadratic classifier with DM-HSISD model showed the best performance at laboratory scale with the classification accuracies of 94.98% and 93.80% for training and testing datasets, respectively. Another quadratic classifier (with DM-HSI model) containing all 39 textural features was found to be the second best with the accuracies of 94.29% and 91.46% on training and test datasets, respectively. The linear classifiers didn’t perform well compare to their respective quadratic counter-parts. Field performance of the developed system equipped with the quadratic DM-HSISD classifier indicated no significant difference between variable rate (VR) and uniform application (UA) in terms of mean percentage area coverage (PAC) for the targeted goldenrod spots in both fields. However, a significant difference was observed between mean PAC of VR and UA applications for the non-targeted wild blueberry spots. The potential and actual chemical savings were in ranges between 46.71% and 74.83% and 30.12% and 60.58% depending on the weed and sprayed area, respectively. These results demonstrated that the developed weed detection system has potential for targeted application of agrochemicals to control goldenrod in wild blueberry fields.

A Numerical Simulation Model for Highbush Blueberry Under Drought Stress

This investigation considered the problem of determining irrigation conditions under which the impact of water deficit stress on a blueberry plant would be minimal. Specifically, and as a first methodological step, we solved the problem of simulating numerically the soil-water-plant system, assuming a scenario of water stress resulting from drought. The main justification for this investigation is the difficulty of obtaining experimental data, and the almost total absence of applications of this methodology to stress conditions for this crop. The simulations are based on the Richards equation with an explicit term, which models blueberry root water uptake, and were executed with HYDRUS-1D software. This software, the Richards equation, and the numerical values used have been widely validated by agronomists in experimental studies of similar crops. Two soil types were simulated: a clay soil and a sandy loam. It was possible to simulate realistic irrigation conditions for a blueberry crop in a scenario of water stress resulting from drought. The results obtained provided sufficient justification of the methodology for subsequent application in field studies.

Testing a Novel Attract-and-Kill Strategy for Drosophila suzukii (Diptera: Drosophilidae) Management.

The invasion of the spotted wing drosophila, Drosophila suzukii Matsumura, across the Americas and Europe has led to increased insecticide applications to protect fruit crops. This insecticide usage conflicts with integrated pest management programs, as well as harvest, export, and pollination services in the affected crops. A novel management tool was assessed against D. suzukii that may mitigate these conflicts. HOOK SWD, an attract-and-kill (A&K) formulation applied as a sprayable bait, was evaluated for three growing seasons in two berry crops in New Jersey and California. In blueberry crops treated with HOOK SWD, fruit infestations by D. suzukii were 2–8 times lower than in untreated crops. In trials in commercial raspberry fields, weekly or biweekly HOOK SWD applications combined with a single grower standard D. suzukii-targeted cover spray resulted in nearly 2–5 times fewer fruit infestations compared to the grower standard cover spray alone. Assays of the residual activity of HOOK SWD resulted in more than 78–93% adult D. suzukii mortality when exposed to raspberry leaves after the formulation had aged for 35 d in the field under plastic hoop houses. These results suggest that this A&K strategy can be integrated in D. suzukii management programs.

Wild pollinators improve production, uniformity, and timing of blueberry crops

Animal pollination is an important input to the global food system, affecting 2/3 of crops and worth more than $100 billion annually. Mounting evidence of pollinators’ importance, and of their decline worldwide, has prompted efforts to conserve and restore wild bees within agricultural regions. To date, however, research on the value of wild pollinators has focused largely on crop productivity per se and on intensely managed landscapes. Here, we combine field experiments, bee observations, and economic methods to estimate the impact of wild pollinators on the quantity and quality of blueberry crops within a low intensity agricultural landscape in Vermont, USA. Visits by wild bees reduced pollination limitation and increased seed set by up to 92%, fruit mass 12%, and fruit set 12%. Visitation also increased the uniformity of fruit size by up to 11% and advanced the timing of harvest by 2.5 days, both of which can increase crop value. For five out of six groups of wild bees, increased visits improved seed set relative to hand-pollinated controls. The potential economic value of relieving pollen limitation (and therefore improving fruit set and fruit mass) varied widely among farms. On most, production could increase 1–6% (representing $500-$4000 per year in additional revenue), but the maximum increase was 36% (representing $137,000 per year). Conserving wild pollinator communities, therefore, can increase crop quantity, quality, and farm revenue, but some farmers will benefit more than others. Farm-specific studies and recommendations are needed to best inform local and regional management decisions.

The Use of Irrigation for Frost Protection for Blueberry in the Southeastern United States

Freeze events between January and April can result in major crop and economic losses for growers of low-chill, early-ripening varieties of blueberry (Vaccinium sp.) in Florida and Georgia. The objective of this research was to determine current responses by blueberry growers to freeze events. Blueberry growers in Florida and Georgia were surveyed about frost protection decision criteria. Growers had differing opinions on when to make the decision to frost-protect blueberry crops. Almost all (98.9%) of the respondents (n = 94) who reported using at least one method of active frost protection reported using irrigation. Farm size, as measured by blueberry acreage, did not influence decisions regarding the use of active frost protection measures. Blueberry growers, on average, reported that a loss of up to 30% to 39% of their crop could be tolerated and still produce a marketable crop. However, they may have been overly cautious at the early bud stages, with ≈40% and 55% of respondents protecting at the bud swell and tight cluster stages, respectively. Understanding the use of irrigation as a frost protection practice in the southeastern United States can aid in improving frost protection recommendations, helping growers maximize yield and saving water and money.

Landscape-scale forest cover increases the abundance of Drosophila suzukii and parasitoid wasps

Agricultural landscapes rich in natural and semi-natural habitats promote biodiversity and important ecosystem services for crops such as pest control. However, semi-natural habitats may fail to deliver these services if agricultural pests are disconnected from the available pool of natural enemies, as may be the case with invasive species. This study aimed to provide insights into the relationship between landscape complexity and the abundance of the recently established invasive pest species Drosophila suzukii and a group of natural enemies (parasitoid wasps), which contain species that parasitize D. suzukii in native and invaded ecosystems. The importance of landscape complexity was examined at two spatial scales. At the field scale, the response to introduction of wildflower strips was analysed, while the relationship with forest cover was assessed at the landscape scale. Half of the surveys were done next to blueberry crops (Vaccinium corymbosum), the other half was done in landscapes without fruit crops to examine effects of D. suzukii host presence. As expected, the number of observed parasitoid wasps increased with amount of forest surrounding the blueberry fields, but the number of D. suzukii individuals likewise increased with forest cover. Establishment of wildflower strips did not significantly affect the abundance of D. suzukii or parasitoid wasps and insect phenology was similar in landscapes with and without blueberry crops. This suggests that D. suzukii is enhanced by landscape complexity and is largely unlinked from the species group that, in its native range, hosts key natural enemies. Although management practices that rely on enhancing natural enemies through habitat manipulations can contribute to the long-term stability of agroecosystems and to control agricultural pests, other control measures may still be necessary in the short term to counteract the benefits obtained by D. suzukii from natural habitats.

Estimation of the Economic Efficiency of Blueberry According to the Production System

Abstract Currently, the blueberry crop systems are continuous diversifing due to the growing demand for fruit on the market as well as the willingness of farmers to invest in profitable blueberries business. The need to extend the fresh-consumption period of blueberry fruits has made crop protection systems be considered appropriate for high-quality and valuable fruits. In the present work, we have proposed to compare the economic efficiency of three blueberry production systems as follows: the normal intensive cultural system in beds, the superintensive cultural system in pots and the superintensive cultural system in pots and plastic covered (high tunnel). The analyze of the cost and profitability of blueberry has been done according to the crop system, taking into consideration several elements such as: the number of plants per hectare, the total duration of the exploitation, the value of the investment, the yield and the cost of production etc. Further more, considering the average sale price of the blueberry fruits in Romania, we have calculated the net annual return, the annual return rate, the cost recovery period, total operating profit, economic return on investment, and average return on investment. We observed that as much the degree of intensification has increased, the value of investment was higher and the spendings has increased too. Blueberry pot production systems with or without plastic protection are especially recommended for smaller surfaces, which in this way can boost the value and their economic potential.

Optimising the parameters influencing performance and weed (goldenrod) identification accuracy of colour co-occurrence matrices

Wild blueberry crop yields are dependent on heavy agrochemical applications to control weeds competing with the crop. Goldenrod is a creeping herbaceous perennial weed that occurred in 90% of wild blueberry fields surveyed in Nova Scotia. A colour co-occurrence matrices (CCMs) based algorithm can be used for spot-application of herbicide on goldenrod within wild blueberry fields. The objective of this study was to analyse the effect of different parameters on computational complexity and goldenrod identification accuracy of CCMs in wild blueberry cropping system. An image acquisition graphical user interface (GUI) and CCMs based textural analysis algorithm were developed in Microsoft Visual® C# programming language. The GUI was used to acquire 2244 area of interest images along with a set of 2244 full frame images from two different wild blueberry fields in central Nova Scotia, Canada. Six image intensity levels, seven image sizes, and three CCMs were used to for the study. The results indicated that intensity levels and image size significantly influenced the computational requirements of CCMs. Images with 256 or 128 intensity levels could be used as these levels correctly classified 94% and 89% of test observations respectively. The processing times were increased from 535 μs to 10,650 μs and 9864 μs to 63,750 μs as the intensity increased from 8 to 256 levels and image size increased from 16 × 16 to 1024 × 1024 pixels, respectively. The time required for textural feature extraction was not statistically significant for different image sizes used in this study. Overall, the results indicated that intensity levels of 128 or 256, a unit image size of 128 × 128 pixels, and saturation colour plane alone or in combination with hue can help to minimise the processing burden without compromising the classification accuracy for real-time applications.

English

The aim of this experiment was to evaluate the effects of nitrogen fertilization on the blueberry crop throughout three consecutive years with different rates and ways of fertilizer application. The experiment was carried out in a commercial orchard located at the county of Vacaria-RS, in Southern Brazil utilizing the blueberry cultivar ‘Bluecrop’. The treatments consisted of the broadcasted nitrogen rates: 0, 50, 100 and 150 kg.ha-1 to verify the crop’s responsiveness to nitrogen fertilization. Looking for the best way of evaluating nitrogen deliverance, a second experiment was conducted in which a fixed rate of 150 kg.ha-1 of nitrogen was broadcasted and applied through fertigation. The nitrogen sources used in both fertilization systems were a mixture of half urea and half ammonium sulphate. Crop yield, number of fruits per plant and mean fruit weight were evaluated during three consecutive years, along with the levels of nutrients in the soil and leaf tissue after three years of broadcasted fertilization. The broadcasted nitrogen fertilization after three consecutive years reduced the soil pH and enhanced the aluminium saturation, but it increased the nitrogen and sulphur uptake by the leaves and reduced the leaves calcium content. These aspects led to a yield reduction of the blueberry crop. Weather conditions affected the efficiency of the N application method (broadcasted or fertigated). Key words: Nitrogen fertilization, soil pH, Vaccinium corymbosum.

Predicting abundance and productivity of blueberry plants under insect defoliation in Alaska

ABSTRACTUnprecedented outbreaks of defoliating insects severely damaged blueberry crops near Port Graham on the Kenai Peninsula in Alaska from 2008-2012. The Native people in this region rely heavily on gathered blueberries and other foods for sustenance and nourishment. Influences of topography and stand structure on blueberry abundance and fruiting were examined and used to develop spatial models to predict abundance and productivity of blueberry plants. Fruiting was associated with decreased canopy density, a low basal area and southwesterly aspects. Stands with relatively high site indices have greater abundance of blueberry plants, while the opposite trend was observed with productivity. Results demonstrate the feasibility of modeling the abundance and productivity of blueberry plants using easily obtained satellite imagery in conjunction with a well-organized field data collection system.

Land Suitability Evaluation for Blueberry Crop by Determining the Qualitative Properties of the Identified Soil Type Related with the Antioxidant Capacity of Fruits

Organic and inorganic forms of nitrogen and carbon were measured in order to determine soil fertility. The amount of total nitrogen ranged between 0.849 g/kg and 1.755 g/kg in the samples gathered from soil in modified state and between 0.961 k/kg and 2.427 g/kg in the samples collected from the soil in natural state. Based on these results it could be concluded that in comparing with the previous year, plants used the soil nutrients for their development. The activities of different enzymes were measured as well. Nitrate reductase activity was also higher in samples collected from soil in modified state (from bilon) than in the samples collected near plantations (control samples) and the values ranged between 0.055 ± 0.012 μmol⋅h-1⋅g-1 and 1.018 ± 0.117 μmol⋅h-1⋅g-1 in samples from soil in natural state and between 0.013 ± 0.002 μmol⋅h-1⋅g-1 and 0.447 ± 0.083 μmol⋅h-1⋅g-1 in bilons. Using GIS techniques of spatial analysis to determine the exact type of soil from each studied blueberry plantation from the Northwest Region of Development and also based on the soil bio-chemical analyses, it was possible to achieve a qualitative characterization of the territory, taking into account the requirements of blueberries for cultivation and to achieve a land suitability for blueberry crop. Combining laboratory approach, consisting from soil bio-chemical and physico-chemical analyses and chemical analyses of blueberry fruits, with the techniques used in order to determine the soil type and land suitability, the study conducted in the Northwest Region of Development identified the best conditions for blueberry crop, based on the qualitative characterization of land.

The Suitability and the Bio-chemical Characteristics of Soils from the Northwest Region of Development from Romania, for Blueberry Crop

We conducted several bio-chemical analyses on soil samples collected from eight blueberry plantations from Northwest Region of Development, using such as Kjeldahl method for total N, Perucci, Krawczyński, Hoffman and Teicher methodology for determine soil enzyme. The bio-chemical analyses conducted provide a better qualitative characterization of soils, providing significant information regarding their fertility degree and favourability for blueberries. For instance, the higher amount of total organic carbon found in four of the eight studied plantation, can be correlated with the same higher amount of enzyme present in soil which have an influence on them, xanthine oxidase and peroxidase activity. Taking into account the requirements needed for a blueberry plantation, we demonstrate that organic soils have also had the highest amount of bio-chemical compounds, such as cambisoil, met in Galații Bistriței, where were also found the highest amounts of different forms of nitrogen (1.755 g/kg total N; 0.0189 g/kg NH4 + and 0.0231g/kg NO3 in Galații Bistriței, comparing to 1.344 g/kg of total nitrogen; 0.0126 g/kg NH4+ and 0.0119 g/kg NO3- in Ulmeni), different forms of carbon and the enzymes that influence this compounds in soil, xanthine oxidase activity, peroxidase activity and nitrate reductase activity.

Verteilung des Wurzelsystems bei Kulturheidelbeeren unterschiedlichen Alters auf mittelschweren Böden

The paper deals with the spatial distribution of root density in highbush blueberry plantations of various ages for a proper planting distance recommendation and a better irrigation and fertilization management. The environmental conditions consist of sandy-loamy soils and a continental temperate climate. Two highbush blueberry cultivars were studied, ‘Bluecrop’ and ‘Blueray’. Root density (RD) and density of root cross-sectional area (RCSA) were investigated for various root diameters. It was found that the prevalent type of roots in highbush blueberry crops is the hair type, with root diameters less than 0.1 mm. Both RD and RCSA decreased with distance from plant and with soil depth; the 38-year-old crop showed a more developed root system versus the 8‑year-old crop. In both cases the roots did not grow more than 0.6 m laterally and more than 0.7 m deep. According to these results, the planting distances in highbush blueberry could be reduced to substantially increase the number of plants/ha and fruit yield. Irrigation application should be carried out to wet a proper soil volume, about 0.6–0.7 m deep for older crops, and about 0.5 m deep for younger crops.

Infestation of Wild Fruit byDrosophila suzukiiSurrounding Maine Wild Blueberry Fields1

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is an invasive vinegar fly that attacks a large variety of soft fruits including wild blueberries in Maine. Wild blueberry fields in Maine are commonly surrounded by woodland edges that contain wild fruit. These edges are important refugia as they provide the fly with needed shade and moisture during the hottest parts of the day. The wild fruit in these wooded edges are also potential alternative hosts for D. suzukii. We surveyed wild fruit along blueberry fields to determine the types of fruit present and measured D. suzukii infestation levels in surveyed fruit. We also measured the number of adult D. suzukii along field edges and the level of infestation in the wild blueberry crop. Drosophila suzukii was found in nine out of seventeen surveyed wild fruit species along field edges. Our results suggest a correlation between wild fruit infestation levels and adult fly densities in the crop fields. Blueberry fields with higher levels of wild fruit infestation also showed higher levels of adult D. suzukii trap captures in the commercial blueberry fields. These wild fruit hosts may allow D. suzukii to increase its population abundance prior to moving into commercial blueberry fields.