David E. Yarborough

Factors Contributing to the Increase in Productivity in the Wild Blueberry Industry

SUMMARY Wild blueberries (Vaccinium angustifolium Ait.) are unique in that they are commercially grown in the State of Maine in the United States and in Quebec and the Atlantic Provinces of Canada. Approximately half the crop is grown in Maine and the remainder from Canada. The wild blueberry crop has increased by an average of 2.3 million kg each year over the last 20 years and now averages over 68.2 million kg per year. Since 1980, approximately 4050 new ha added in Maine, and over 6073 ha have been added in New Brunswick and Nova Scotia; PEI has also developed more than 1620 new ha. However, most of the gains in yield have come from improved management of the fields. Preemergence weed control with the herbicides terbacil and hexazinone in the 1980s provided a release from the weed competition, and immediately doubled yields on many fields. It also allowed for improved fertility management and the increased use of bees for pollination which resulted in even more production. Good disease and pest control using integrated pest management keeps crop losses from pests to a minimum. Recently, in Maine, there has been an investment in use of irrigation, with approximately 3,000 ha of in-ground irrigation and 850 ha of above-ground irrigation now in use. Recent research has shown a 43% increase in yield with irrigation. All of these factors have combined to produce a three fold increase in the wild blueberry crop over the past 20 years. Mechanical harvesting has increased but is only used on a small percentage of the Maine crop, whereas more than half of the Canadian crop is harvested mechanically. This contributes to the efficiency of production since it reduces the cost of the most expensive production practice.

An Overview of Weed Management in the Wild Lowbush Blueberry—Past and Present

SUMMARY The wild lowbush blueberry (Vaccinium angustifolium Ait.) is an important successional species of cleared woodland and abandoned farmland of northeastern North America where commercial, managed blueberry fields have been developed. Unlike other fruit crops, the weed flora is unique and consists mainly of a broad range of native herbaceous and woody perennial species that thrive under the two-year cropping system. Traditionally, weedy vegetation was controlled or suppressed by burning, cutting, and roguing, and regenerating woody and herbaceous species were the major weed problems. The introduction of phenoxyalkanoic herbicides in the late 1940s lead to the early development by innovative growers of selective roller/wiper applicators that could control the taller, weedy overstory. Several selective preemergence herbicides (terbacil and diuron) were introduced in the 1970s to control grasses and some broadleaved weeds, and hexazinone was approved in Canada in 1982 and in Maine in 1983. This soil-applied, broad spectrum herbicide has controlled many of the common woody and herbaceous weeds. Its widespread use lead rapidly to increased yields and, directly or indirectly, it has contributed to changes in other production practices, such as the further development of mechanical harvesters and increased fertilizer use. However, the almost total reliance on the repeated use of hexazinone has introduced other problems, including shifts in weed species, the development of resistance, and soil degradation on vegetation-free soils. The highly soluble nature of the herbicide has resulted in wide-spread detection of hexazinone in groundwater adjacent to managed blueberry fields. Best Management Practices have been introduced to minimize problems associated with hexazinone use and is leading to new approaches to vegetation management that employ reduced risk herbicides, lower rates, mulches and ground covers.

Lowbush Blueberry (Vaccinium angustifolium) with Irrigated and Rain-Fed Conditions

SUMMARY Growers desire a better understanding of the effect of irrigation on lowbush blueberry (Vaccinium angustifolium) crop yield and quality. A randomized block design of irrigated and rain-fed plots was established in a lowbush blueberry field near the coast of Maine. The irrigated plots averaged 43% higher yield than rain-fed plots for the 2000-2001 production cycle. Irrigated plots had the highest yield three weeks after the highest yield for the rain-fed plots. Rain-fed berries had greater firmness, higher Brix solids and lower moisture content than irrigated berries for three different harvest dates. Berry size distribution was not significantly different for treatments, but for different harvest dates the berry size distributions were significantly different.

Determination of Evapotranspiration and Drainage in Lowbush Blueberries (Vaccinium angustifolium) Using Weighing Lysimeters

SUMMARY Lowbush blueberry growers need recommendations for irrigation scheduling. This study was conducted to determine irrigation water use potential. Initial data were collected from the end of April through early August 2002 using weighing lysimeters to measure evapotranspiration and drainage. High rainfall and drainage rates near the end of April indicated a period of rapid leaching when chemical applications could be beneficially postponed. Nighttime increases in lysimeter weight were observed indicating that direct vapor deposition is a significant factor in the water balance. Results from this ongoing study will be used for scheduling irrigation water applications to improve water use and production efficiency.

Evapotranspiration Rates and Crop Coefficients for Lowbush Blueberry (Vaccinium angustifolium)

ABSTRACT Lowbush blueberry (Vaccinium angustifolium) yield is strongly influenced by water availability; however, growers need more specific irrigation recommendations in order to optimize water use efficiency. Weighing lysimeters were used to determine actual evapotranspiration (ET) rates of lowbush blueberry at one nonirrigated and two irrigated sites within 7 km of the Maine coast. For the three-year study period, overall mean weekly ET rates (with standard errors) during June, July, and August were calculated to be 2.13 (±0.05), 2.39 (±0.07), and 2.19 (±0.07) cm/wk, respectively. Mean monthly ET rates did not differ significantly between irrigated and nonirrigated sites. Crop coefficient (Kc) values were determined from the ratio of daily Penman-Montieth grass reference ET to measured daily ET. The combined mean monthly Kc values for the two irrigated sites varied between 0.61 and 0.74 from May through September, with an overall mean Kc value for all sites of 0.69 (±0.02). The Kc values showed no significant rotation-year component. Consequently, the Kc value determined in this study can be used in conjunction with meteorological data to provide Maine lowbush blueberry growers with the ability to better predict water demand by their crop. Fog at the irrigated sites was found to contribute approximately 13.5 cm of net water equivalent per growing season. However, the effects of dew formation and fog deposition are already reflected in the Kc value for each site, enabling growers to determine water demand from these values and grass reference ET data alone. These findings may substantially contribute to improved water use efficiency for irrigated lowbush blueberry in Maine.

Organic Lowbush Blueberry Research and Extension in Maine

A six-year organic systems research project was conducted in Maine from 2004 to 2009. The project had several components: (1) a large replicated interdisciplinary multifactor (fertility, weed, insect, and pathogen) experiment over three cropping cycles (6 years), (2) single disciplinary experiments designed to develop organic management tools for pest management, (3) an economic analysis of current organic production, (4) a survey of organic growers for the purpose of deriving a descriptive profile and the development of grower case studies, and (5) organic Extension workshops and field meetings and production of an organic wild blueberry growers guide. This article highlights some of the outcomes of this project including: ecological interactions among pests and fertility, novel management tactics, niche-market diversity, and economic viability.

Influence of Coastal Proximity on Evapotranspiration Rates and Crop Coefficients of Maine Lowbush Blueberry (Vaccinium angustifolium)

Supplemental irrigation can be a viable means of increasing lowbush blueberry (Vaccinium angustifolium) crop yields in humid environments. To best utilize this management technique, Maine growers require accurate knowledge of regional crop water demands. Meteorological data and weighing lysimeters were used to determine Penman–Montieth grass reference evapotranspiration (ETo) rates and actual evapotranspiration rates of the lowbush blueberry at five irrigated and two nonirrigated fields of varying distance from the Maine coast. Mean daily values of air temperature, relative humidity range, and solar flux were all found to increase with increasing distance from the coast. The frequency of growing season fog hours increased from 3.7% of all hours at a distance of 22.5 km from the coast, to 11.1% of all hours at a distance of 0.8 km from the coast. Water equivalent inputs from fog per growing season at these two sites averaged 7.2 cm and 18.3 cm, respectively. These geographic climatic differences were reflected in the calculated evapotranspirationo rates, which also generally increased with distance from the coast. Four-year mean weekly ETo rates for July, the month of greatest potential water demand, were 2.76 cm/week, 3.21 cm/week, 3.52 cm/week, and 4.23 cm/week for sites located 0.8 km, 6.4 km, 22.5 km, and 48 km, respectively, from the coast. Actual ET rates for both crop and prune rotations followed a similar pattern of increasing magnitude with distance from the coast. For July, mean crop and prune year pooled weekly ET rates at 0.8 km, 6.4 km, and 22.5 km from the coast were: 1.69 cm/week (0.85), 2.28 cm/week (0.73), and 2.40 cm/week (0.83), respectively. Standard condition crop coefficient (Kc) values for both rotations during the months of May through September were calculated to be 0.68 for sites 6.4 and 22.5 km from the coast. Thus, it would appear that the same Kc value can be used universally within the typical growing range of the Maine lowbush blueberry. These findings should substantially contribute to improved water use efficiency for the irrigated lowbush blueberry in Maine.

Evaluating field inputs for productivity and profitability in wild blueberry fields in Maine

The goal of the project was to provide growers with information on how different management systems affect the crop, its environment and the ecological and economical sustainability of wild blueberry production. A critical issue affecting growers is how to optimize increasingly expensive inputs to achieve economically and environmentally sustainable yields. We conducted a multi-disciplinary large-scale study of four cropping input systems consisting of Organic, Low input, Medium input and High input that provided diverse gradients of capital inputs and potential environmental effects to quantify system effects on yield, fruit quality, pest communities, the environment, and economic effects of inputs. In the 2010 to 2012 cycle, the cropping systems were applied to two fields (n=8 fields), and this was expanded to have each of the cropping systems applied to an additional four fields (n=16 fields) in 2011 to 2013. This paper will discuss the fertility and weed aspects of the study. Leaf and soil samples were taken in the non-bearing years, and weeds and blueberry were evaluated in June and July. There was large variation on variables measured between years and among locations. Leaf nutrient levels were highest at the High input sites with N, P and B much higher and on the Organic input sites leaf nutrient levels for N and P were deficient but Ca was higher. Weed cover was highest in Organic and Low input systems. Yields were highest in the High input system, but with higher costs it was not the most profitable. Data from both years verify trends that the Medium input system was the most profitable. The Low input system was not profitable on most sites. Organic yields were lowest but with higher fruit value were profitable. INTRODUCTION Munson (1898, 1901) first described the wild blueberry (Vaccinium angustifolium) in Maine and its potential for culture as a crop and possible ornamental use. The wild blueberry barrens in Eastern Maine comprised 150 thousand acres; its management consisted of burning the fields over and hand-picking for the fresh market and raking for the canning market. Chandler and Hyland (1941) and Hall (1978) described the growing economic importance and distribution in Maine and Atlantic Canada, respectively. Hepler and Yarborough (1991) found that although there was great genetic variability in wild blueberry fields, the average yield under intensive management could obtain and average 7,726 kg/ha with a maximum yield of 17,000 kg/ha. Smagula and Yarborough (1990) first described the changes in pruning management from the traditional burning to flail mowing and the beginning of mechanical harvesting. Yarborough (1997) documented a tripling of the wild blueberry yield in Maine over the previous 15 year period with increases in the intensity of management without increase of the land base. Yarborough (2004) elaborated on the improvement in weed, fertility and pest management, increased use of honey bees for pollination and irrigation to continue to improve the productivity of wild blueberry fields in Maine, and the addition of increased production and land base in Quebec and Atlantic Canada. Strik and Yarborough (2005) documented that the increase in both cultivated (V. corymbosum and V. ashei) and wild blueberry production was principally from increased number of hectares under production. An educational program was instituted to help wild blueberry growers improve production efficiency, develop enterprise budgets (Yarborough et al., 2003), develop business and marketing plans (Anon., 2011), eliminate marginal and unprofitable operations and improve production on the most viable fields. Research conducted on organic wild blueberry production using a systems approach identified that the use of burning for pruning combined with sulfur to reduce weed competition could triple the yields for organic producers, and Drummond et al., (2012) developed a path systems model to identify causal effects and correlations among the factors influencing production. The objective of this multi-disciplinary large-scale study of four cropping input systems Organic, Low input conventional, Medium input conventional and High input conventional that fit along gradients of capital inputs and potential environmental effects was to quantify system effects on yield, fruit quality, pest communities, the environment and the economic effects of inputs. This paper focuses on the fertility and weed management aspects of this study, and evaluates the systems’ effects on yield and returns to production. MATERIAL AND METHODS In spring of 2010, a four-year study was initiated using a systems approach to evaluate the effects of four different cropping management systems: Organic, Low, Medium and High input, characterized by the inputs following the parameters in Table 1. Growers were asked to perform their usual activities within these blocks as part of the larger field management. Wild blueberry is managed on a two-year crop cycle; the first year of a cycle is a non-bearing year and the second a cropping year. The project has completed two crop cycles from 2010 to 2013. In the first cycle of the study, each input system consisted of two fields with four one acre blocks each, containing nested 15 x 30 m sampling sub-blocks, each with four 15 m transects used for subsampling for a total of eight sites and 32 blocks. In the second cycle, each input system consisted of four sites with two one acre blocks set out, and as in the first year containing nested 15 x 30 m sample sub-blocks with four 15 m transects each for a total of 16 fields and 32 blocks (Fig. 1). Along the 30 m baseline (the outer long edge) of each sub-block, four 15 m long transects were located 5 m apart in order to set up 1 m sample plots to assess weed cover. One, 1 m sample plot was staked on each transect in such a manner that the sample plots ranged diagonally across the sub-block. For example, in a 15 x 30 m sub-block, transects were located at 5, 10, 15 and 20 m along the 30 m baseline. Within this sample plot A was located at 3 m on the first transect, B at 6 m on the second, C at 9 m on the third and D at 12 m on the fourth (Fig. 2). Although this study also looked at many other aspects of production, including plant disease, pathogens for food safety, fruit quality, insects, pollinators, and soil chemistry and health, this study will only cover the fertility, weeds, yields and economic returns. Table 1. Management systems overview of inputs for 2010 to 2014. Production Factors Organic Low Input Medium Input High Input Pruning Burned Burned Mowed Mowed Land leveling Not land leveled Not land leveled Land leveled Land leveled pH management pH may be managed No pH management pH managed pH managed Fertility No fertilizer Some fertilizer Fertility (both cycles) Fertility rate much higher Pest, disease, and weed control Weed whacking, cutting woody weeds, grazing with goats, no pesticides used Herbicides insecticides, some sites with fungicides Scouting, herbicides, insecticides, fungicides crop year Scouting, herbicides, insecticides, fungicides in both years Treatment of bare spots Mulch No mulch No mulch Mulch Irrigation No irrigation No irrigation No irrigation Irrigation as needed Pollination Bees 0 to 2 hives/acre Bees 1-3 hives/acre Bees 2 hives/acre Bees 5-7 hives/acre Harvest method Hand raked Hand raked Mechanical harvest Mechanical harvest Figure 1. Location of fields in the second cropping cycle by management system. Figure 2. Example layout of an acre block, 15 x 30 m sub-block and 15 m transects. In each one acre block at each management site, soil was sampled in July 2010 and 2012 using a standard soil sample tube removing a 2 cm diameter core 7.6 cm deep. Forty cores, collected by sampling along two diagonal transects in each block were combined and analyzed for soil pH (water), organic matter and nutrients. Organic matter was measured by loss on ignition (LOI) at 375° C. Available nutrients were extracted in pH 4.8 ammonium acetate (Modified Morgan method) and measured by plasma emission using a TJA Model iCAP 6300 ICP-AES. Composite leaf tissue samples from 50 stems were also sampled in early July along the same diagonal transects to determine leaf nutrient concentrations (Trevett et al., 1968). Leaf samples were prepared according to the methods of Kalra and Maynard (1991) and submitted to the University of Maine Soil and Plant Tissue Testing Laboratory for nutrients analysis. Data were analyzed by ANOVA with mean separation obtained by Duncan’s Multiple Range Test at the 5% level. Blueberry cover, woody weed cover, broadleaf weed cover and grass cover were assessed in all 1 m sample plots approximately one and three months after the timing of pre-emergence weed control in the High and Medium input systems (early June and late August) each year. The 15 x 30 m sub-blocks were weed whacked using a string trimmer above the height of the blueberry plants in June, July and August in the Organic system only. Blueberry and weed cover in the Organic system were assessed prior to the June and August weed cutting. Weed and blueberry cover were assessed using the Daubenmire Cover Class scale (Muller-Dombois and Ellenburg, 1974), which was converted to percent cover, and weed species were also identified. Because the data failed the assumptions of the General Linear Model, the data were analyzed using a nonparametric one-way median exact test (α=0.05). The overall blueberry cover and weed cover comparisons were made among all treatments; therefore, a Bonferroni adjustment was applied (α=0.0125). Weed cover values were plotted against yield via linear regressions, and significance was determined by a hierarchical or nested general linear model SAS PROC GLM (SAS Institute Inc., 2006). All sites were harvested the first week of August in 2011 and between 30 July and 6 August in 2013. The blocks were harvested along the 15 m long transects, and went through

Effect of Pine Bark Mulch on Lowbush Blueberry (Vaccinium angustifolium) Water Demand

Mulching has been reported to moderate soil temperatures, lessen the erosive effects of rain, suppress weeds, and reduce evapotranspiration losses from crops worldwide. Lowbush blueberry (Vaccinium angustifolium) growers seeking an alternative and/or a complement to supplemental irrigation require accurate crop-specific information on the water conserving benefits of mulch. Twenty-eight weighing lysimeters equipped with soil moisture monitors were used at five sites throughout the Downeast Region of Maine to compare water budgets of lowbush blueberry grown on un-mulched and mulched soils. Despite occurrence of the second wettest growing season in 60 years, April through September mean hourly soil water potential values at all sites indicated significantly (p < 0.001) drier conditions in un-mulched compared with mulched soils. Differences in soil water potential values between un-mulched and mulched soils were much more pronounced during three dry periods, totaling approximately 53 days, than during the 2009 growing season as a whole. Over the course of one 27 day dry-period, soil water potential values of un-mulched soils at two lysimeter stations indicated a need for irrigation more than 60% of the time, compared with 7–10% of the time for mulched soils. Mulching was found to reduce diurnal fluctuations of both soil water potential and volumetric water content. Early morning water deposition was significantly reduced by mulching at nearly all lysimeter stations; however, mulch-associated reductions in peak-hour evapotranspiration losses more than compensated for lower water inputs from dew and fog. During the three major periods of dry conditions, mulch reduced the evapotranspiration rate by an average of 0.045 ± 0.003 cm/day at three crop-rotation fields and 0.039 ± 0.027 cm/day at four prune-rotation fields. The greater variability in evapotranspiration rate reduction found among prune-rotation fields was considered due to differences in pruned shoot emergence from the mulch. These results indicate that mulching represents a viable method for alleviating drought-induced water stress for lowbush blueberry in Maine.

The Economics of Supplemental Irrigation on Wild Blueberries: A Stochastic Cost Assessment

SUMMARY Wild blueberry growers face numerous production perils of which drought and heat produce the greatest losses. Using partial budgets, this research derives stochastic cost estimates of four alternative irrigation technologies that apply supplemental irrigation to wild blueberries. Uncertain parameters related to irrigation water demand are subjected to Monte Carlo simulation to derive the expected distribution of total annual irrigation costs. This study finds that labor and energy intensive systems supply water more cost effectively to Maine producers due to limited overall demand for irrigation water. In addition, the total annual cost of irrigation is highly site specific and necessitates spatially disaggregated estimation of costs.