Organic fruit production in British Columbia

Organic fruit production in British Columbia G. H. Neilsen1, D. T. Lowery1, T. A. Forge2 and D. Neilsen1 Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, 1Summerland, British Columbia, Canada V0H 1Z0 and 2Agassiz, British Columbia, Canada V0M 1A0. Received 16 September 2008, accepted 2 April 2009. Neilsen, G. H., Lowery, D. T., Forge, T. A. and Neilsen, D. 2009. Organic fruit production in British Columbia. Can. J. Plant Sci. 89: 677
692. British Columbia has climatic conditions suitable for the production of a wide range of high-value fruit crops, and has the highest rate of increase of organic production in Canada. This review assesses the current status of organic fruit production using a case study of the three most valuable fruit crops currently grown: apple (Malus  domestica Borkh.), grape (Vitis vinifera L.) and high bush blueberry (Vaccinium corybosum L.). The review emphasizes the current status of organically acceptable management of crop resources and crop protection from insects and diseases. Central to organic production are soil management strategies designed to maintain soil fertility and increase soil biological activity and biodiversity by increasing soil organic matter content. Composts and organic amendments that require vigilant testing of their variable and often lower nutrient content are substituted for the chemical fertilizers of conventional production. Increased effort to manage vegetation within and between planting rows is necessitated by an inability to use herbicides. Thus, techniques such as mulching, cultivation and cover cropping are important. Management of insects and diseases requires detailed information of the agro-ecosystem and the unique interactions between pests and specific crops. Organic approaches to minimize pest damage include altered production practices or applications of organically approved control products. Some aspects of organic production systems have received little or no research. In irrigated areas, there is little information available on water management that supports conservation and the specific needs of organic production systems. Historically, research on organic production systems has not received the financial support allocated to conventional system research. Many research needs are identified in this review both applicable to all three fruit crops studied, but also specific to the individual crop. It is argued that future consumer demand calls for an acceleration of research on organic fruit production systems. Key words: Malus domestica Borkh., organic soil, insect and disease management, Vaccinium corybosum L., Vitis vinifera L. Neilsen, G. H., Lowery, D. T., Forge, T. A. et Neilsen, D. 2009. La culture fruitière biologique en Colombie-Britannique. Can. J. Plant Sci. 89: 677
692. Le climat de la Colombie-Britannique se prête à la production d’une grande variété de cultures fruitières lucratives et la province connaı̂t la plus forte hausse au Canada pour ce qui est de la culture biologique. Cet article dresse le bilan de la production de fruits biologiques par le biais d’une étude de cas sur les trois cultures actuellement les plus lucratives, soit la pomme (Malus domestica Borkh.), le raisin (Vitis vinifera L.) et le bleuet en corymbe (Vaccinium corybosum L.). L’article insiste sur la situation actuelle des ressources agricoles exploitées d’une manière biologiquement acceptable et des moyens de lutte biologiques contre les insectes et la maladie. Au cæur de la culture organique figurent des stratégies de gestion du sol conçues pour préserver la fertilité du sol et accroı̂tre son activité biologique ainsi que sa biodiversité par l’addition de matière organique. Les engrais chimiques des systèmes de production agricole habituels sont remplacés par des composts et des amendements organiques nécessitant une vérification constante de leur concentration d’éléments nutritifs, variable et souvent plus faible. L’impossibilité d’employer des antiparasitaires signifie qu’on doit consacrer plus de temps à gérer la végétation dans les rangs et entre ceux-ci, d’où l’importance de techniques tels le paillage, le hersage et l’usage de cultures-abris. La lutte contre les insectes et la maladie exige qu’on soit bien renseigné sur l’écosystème agricole et sur les interactions uniques entre ravageurs et cultures. L’approche retenue par l’agriculture biologique pour minimiser les dommages causés par les parasites comprend la modification des pratiques culturales et l’utilisation de produits de lutte approuvés pour l’agriculture biologique. Certains aspects des systèmes de production biologique ont fait l’objet de très peu de recherches, voire aucune. Dans les régions irriguées, on possède peu de renseignements sur les méthodes de gestion de l’eau qui favorisent la conservation de cette dernière et les besoins spécifiques des systèmes de production biologique. Historiquement, la recherche sur l’agriculture biologique n’a pas bénéficié du même appui financier que celle sur l’agriculture classique. L’article identifie de nombreux besoins de recherche tant pour les trois cultures fruitières examinées que pour chacune d’elles, prises séparément. On présume que la future demande des consommateurs entraı̂nera une intensification de la recherche sur les systèmes de production biologiques pour les cultures fruitières. Mots clés: Malus domestica Borkh, sol organique, lutte contre les insectes et la maladie, Vaccinium corybosum L., Vitis vinifera L. Interest in organic production has increased in Canada due to consumer demand and higher economic returns for growers. This, in turn, has resulted in national (Canadian General Standards Board 2006) and regional (Certified Organic Associations of British Columbia 2005) efforts to increase consumer confidence by Abbreviations: SIR, sterile insect release 677 Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. 678 CANADIAN JOURNAL OF PLANT SCIENCE standardizing organic production practices. Organic production systems which emphasize reduced inputs of pesticides and fertilizers have frequently been cited as being more environmentally sustainable (Reganold et al. 2001; Vogeler et al. 2006; Wood et al. 2006). The production of organic fruit is of particular interest, as greater consumption of fresh fruit is advocated as an essential component of a healthy diet, and there are claims that organic fruit is of higher nutritional quality (Reganold et al. 2001). Interest in organic production is particularly strong in British Columbia, currently increasing at the highest rate in Canada, so that in 2005 13% of Canada’s organic farms were located in British Columbia (http:// www.cog.ca). Increasing interest in organic and sustainable production practices and steady growth in the organic sector is also driven in British Columbia by lifestyle choices, perceived opportunity for green labelling, increasing consumer demand, and the close proximity of producers to urban populations with a heightened sensitivity to environmental issues. For example, the proportion of cultivated area dedicated to organic production for the top 10 most valuable fruit crops ranges from 0.7 to 0.8% of total cultivated area for blueberry, cranberry, raspberry and strawberry to 7.2 and 10.3% for apple and pear, respectively (Table 1). The area of land dedicated to organic crops is currently modest, exceeding 100 ha only for apples (Table 1). Although the area of each organic fruit crop is not reported separately for all fruit crops in all provinces, in 2005, British Columbia production represented 29, 43 and 100% of total Canadian area reported for blueberry, apple and grape, respectively. Given the importance of high-value fruit production in British Columbia and the growing interest in organic production, it seemed an opportune time to review organic fruit production issues with the aim of identifying important research and development needs. This review will use a case study approach by focusing on the three most valuable fruit crops currently grown in British Columbia: apples, grape and blueberry. There are other fruit crops, such as sweet cherry, in the province with good potential for expansion in organic production, but they will not be specifically discussed. Currently, organic growers of apple, wine grapes and blueberry in British Columbia are growing the same cultivars as conventional growers. The review will not discuss the important issue of breeding varieties specifically for organic production systems, as this topic has previously been reviewed elsewhere (Jamieson 2006). Instead, the focus will be on field production issues involving sustainable organic management of crop resources and crop protection from insects and diseases. Both these issues are affected by climatic conditions, which vary considerably within the main commercial fruit production regions of British Columbia (Table 2) creating unique constraints and conferring unique advantages upon organic fruit production in the province. As this is typical of most regions where organic fruit production is contemplated, the British Columbia experience is likely to be of more general interest. Table 1. Farm gate value, cultivated area and per cent of Canadian production value for top 10 woody perennial fruit crops produced in British Columbia, 2005 2006
Crop 1. High bush blueberry (Vaccinium corymbosum L.) 2. Apple (Malus domestica Borkh.) 3. Grape (Vitis vinifera L.) 4. Cranberry (Vaccinium macrocarpon Ait.) 5. Sweet cherry (Prunus avium L.) 6. Raspberry (Rubus idaeus L.) 7. Strawberry (Fragaria x ananassa Duch.) 8. Peach (Prunus persica (L.) Batsch) 9. Pear (Pyris communis L.) 10. Plum/prune (Prunus domestica L.) z Farm gate value ($M)z Cultivated areaz (ha) Portion of Canadian production (%)z Portion organic [% BC cultivated area, area (ha)]y 68.2 3,480 49 0.7 (24) 38.5 4,249 29 7.2 (306) 29.5 2,970 32 2.0 (59) 24.6 1,700 41 0.8x (14) 21.4 1,012 85 2.5 (25) 11.7 1,538 57 0.8x (12) 4.3 1,000 8 0.8x (8) 3.8 405 13 4.9 (20) 2.8 243 30 10.3 (25) 0.9 117 6 5.5 (6) Adapted from 2006 data from Statistics Canada (2007) Fruit and vegetable production catalogue no. 22-003-XIB. Adapted from: http://www.cog.ca/OrganicStatistics.htm. Data a composite for all three crops. y x NEILSEN ET AL. * ORGANIC FRUIT PRODUCTION IN BRITISH COLUMBIA 679 Table 2. Environmental conditions in the three major fruit producing regions of British Columbiaz Location Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. Characteristic Growing degree days (58C) Frost free days Extreme max. temperature (8C) Extreme min. temperature (8C) Mean July max. temperature (8C) Mean Jan min. temperature (8C) Days
308C DaysB108C Moisture deficit (Mar.
Oct.) (mm) Lower mainland (Abbotsford) Okanagan (Summerland) Kootenay (Creston) 1980 233 37.8 21 23.4 0.6 3 7 627 2169 204 40 30 27.1 5.2 13 19 841 1967 195 39.4 32.8 26.5 5.5 15 19 749 z From: http://www.climate.weatheroffice.ec.gc.ca/climateData/canadae.html. ORGANIC CROP RESOURCE MANAGEMENT Soil Management Experimentation with organic agricultural practices initially grew out of a desire to develop holistic farming systems that were regenerative with respect to soil fertility and promoted self-sufficiency (Treadwell et al. 2003). The work of early researchers, such as F. H. King in the United States and Sir Albert Howard and Rudolf Steiner in the United Kingdom in the early 1900s, was focused primarily on composting and the efficient recycling of animal wastes. These early organic systems researchers, with their holistic viewpoints, recognized that enhancing soil organic matter and soil biological activity also influenced the occurrence of pests and diseases (Treadwell et al. 2003). During the modern era of organic agriculture, which has been driven primarily by consumer preferences for pesticide-free food, the focus of organic agriculture has shifted to elimination of synthetic pesticides. Nonetheless, most growers and scientists still recognize that healthy soils form the foundation of holistic approaches to the development and study of organic production systems (Mäder et al. 2002; Treadwell et al. 2003; Pimentel et al. 2005). In addition to providing plant-available nutrients, the organic matter and biological activity of soils influence water availability, insect pests and diseases, particularly soil-borne pests (insects and nematodes) and pathogens. In turn, pest or pathogen management strategies and irrigation practices can influence soil biological activity, decomposition of residues and mineralization of nutrients. The concept of soil health, which differs from the concept of soil quality in its emphasis on the dynamic and biological aspects of soil, is inextricably linked with the growth of organic agriculture. The benefits resulting from increased organic matter content of soils have long been recognized (Tisdale et al. 1993). These include improvements in soil physical properties associated with soil structural modifications that result in increased water-holding capacity, improved aeration, and reduced susceptibility to excessive compaction. Incorporated organic residues release plant nutrients upon decomposition, and due to their abundant chemically reactive compounds increase nutrient exchange capacity and chemically buffer the soil against rapid changes in pH and salinity. Increased reliance on organic matter in organic production systems is usually associated with a greater biomass and diversity of bacteria, fungi, actinomycetes and soil invertebrates than conventional systems (Van Bruggen and Termorshuizen 2003; Pimentel et al. 2005), including populations of arbuscular mycorrhizal fungi, which are known to be beneficial to the performance of fruit crops such as apple and blueberries (Purin et al. 2006). In general, organic soil management practices are expected to increase soil biological activity and enhance root health, but few quantitative studies have directly related these changes in soil biology to crop performance. Using composts and cover crops to enhance overall soil fertility generally results in plants with lower tissue N concentrations compared with conventional production systems. While N limitation may reduce yields somewhat, it can potentially result in reduced disease and insect pest pressures that may compensate for the reduced yields. For example, bacterial blight of blueberry, caused by Pseudomona syringae pv. syringae van Hall, is an economically significant disease of blueberry in British Columbia. Excessive nitrogen fertilization delays development of blueberry cold hardiness in fall and winter, which predisposes blueberry plants to bacterial blight [Bristow and Moore 1995; British Columbia Ministry of Agriculture and Lands (BCMAL) 2006]. Similarly, high nitrogen inputs that promote lush leaf growth in spring also enhance Botrytis blight of blueberry, caused by Botrytis cinerea. Pers.:Fr. Consequently, organically managed blueberry would be expected to be impacted less by bacterial blight and Botrytis blight as a result of lower tissue N concentrations. However, due to the relatively small acreage of organic blueberry in British Columbia, it is not yet clear if there are indeed significant differences in blight incidence between the two production systems. Organic matter and nutrients suitable for organic horticulture can be supplied a number of ways. For Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. 680 CANADIAN JOURNAL OF PLANT SCIENCE perennial fruit crops, these can be divided into two interrelated and overlapping categories: application of exogenous composts or other organic materials (Table 3), and preferential management of vegetation within and between rows. Certification requirements for organic production impose restrictions on suitable soil amendments so that, for example, materials derived in part from genetically engineered crops, containing chemical contaminants, or produced by synthetic processes, are forbidden (Table 3). The subsequent discussion on use of organic amendments and organic cover crops is based on the assumption that only certifiable materials will be used although not all the cited research was conducted under certifiable organic production. Organic Amendments and Nutrient Management Opportunities to incorporate organic amendments into the root zone of woody perennials such as apple, grape and blueberry are limited to pre-plant preparations. Consequently, organic amendments are often surfaceapplied (i.e., as mulches). The use of mulches had the highest suitability of any orchard floor management system as a result of its combination of benefits associated with production of a quality apple crop while maintaining good soil quality (Hogue and Neilsen 1987). Organic mulches not only act as a primary source of nutrients, they also suppress weeds, affect the distribution and availability of water and reduce the abundance or activity of plant pathogens in the root zone. Because organic mulches have multiple functions and influences within an integrated system, it is often difficult to isolate the reasons for improved production that are usually associated with their use. Neilsen et al. (2003) indicate that mulching the apple tree rows with alfalfa, shredded paper or black plastic significantly increases yields during the first five growing seasons relative to the standard commercial production practice involving maintenance of an unmulched herbicide strip (Table 4). Nutrients, as measured for K, increase in the 0 to 0.1 m depth immediately below the alfalfa mulch. The use of shredded paper mulch reduces population densities of root lesion nematodes [Pratylenchus penetrans (Cobb) Schurmans-Steckhoven] and increases the biomass of fine roots in surface soil under the mulch (Forge et al. 2003, 2008). Improvement in soil moisture content is also a frequently reported Table 3. Selected soil amendments suitable for organic productionz Amendment Qualification/limitations Cover crops/green manures No genetically engineered cover crops allowed. Uncomposted manures Potential pathogenic bacteria problem (no contact with edible plant parts). Thermophilic digestion (55
608C) required for several days to kill weed seeds and pathogens. Can be comprised of manures, yard, fish, seaweed, and food wastes. Containing no prohibited materials (e.g., biosolids). Can comprise blood, fish, feather, bone and soybean containing unadulterated components. Composts Meals Mulches Wood chips, sawdust, bark From untreated woods. Shredded paper Containing no metal based inks. Waste paper (spray-On-mulch) Containing no chemical contaminants. Straw (cereals/wheat) Hay (meadow/alfalfa) Pine needles Black polyethylene Liquid Organics Compost teas Liquid fish Humate, Fulvic acid Inorganic Compounds (as a nutrient source or soil amendment) Rock phosphate (P) Greensand (K) Langbeinate (K, Mg) Epsom salts (Mg) Rock powders (K, trace elements), Slyvenite (K) Wood ash (K) Food grade CaCl2 (Ca) Calcium carbonate (Ca, pH adjustment) z As adapted from Organic Associations of British Columbia (2005). Has suitable pH for blueberry. Removed from soil after use. No polyvinyl chloride. Little documented research. Leachate from acceptable composts. Without synthetic preservatives. If mined naturally, unfortified with synthetic fertilizers. Natural products must be unrefined, unmodified and not contaminated If plant nutrient deficiency can be demonstrated, conventional chemical fertilizer can be applied. Additional details Blackshaw et al. (2005) Neilsen et al. (2004) Neilsen et al. (2007) Hogue et al. (2003) Hogue and Neilsen (1987) Stevenson et al. (1986) NEILSEN ET AL. * ORGANIC FRUIT PRODUCTION IN BRITISH COLUMBIA 681 Table 4. Response of Spartan apple on M.9 rootstock and associated orchard soil to maintenance of various mulch treatments commencing in 1994z Cumulative yield Soil properties (0
10 cm depth, 2001) 1995
1999 Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. Mulch treatment 1. No mulch (herbicide strip) 2. Alfalfa 3. Shredded paper 4. Black plastic Total nutrients Extractable nutrients Infiltration rate kg tree 1 N (%) C (%) P (mg kg1) K (mg kg1) (L h 1) 12.9cy 17.3b 23.4a 20.0ab 0.10bc 0.14ab 0.12b 0.09c 1.0d 1.5ab 1.3bc 0.9d 40bc 74ab 26c 29c 140b 515a 126bc 86c 5.5b 15.5ab 10.0b 3.4c z Data adapted from Neilsen et al. (2003). Means within a column followed by the same letter are not significantly different at the 5% level according to Duncan’s multiple range test. y consequence of mulching (Hogue and Neilsen 1987). It is noteworthy that lower organic inputs to the soil surface for a permeable black plastic mulch (Table 4) decrease the K status and infiltration capacity of the soil relative to herbicide or organic mulch treatments, indicating a possible long-term limitation to the use of black plastic mulches. Predicting the nitrogen benefit of an organic mulch is difficult, as the materials vary not only in nutrient content but also in the rate at which nutrients are mineralized. This variation is illustrated by data for various composts, and indicates a considerable range in potential N mineralization from site to site and year to year (Table 5). The availability of N from these sources is affected by the rate, timing and method of application (Gaskell and Smith 2007). As most N in composts occurs as organic forms rather than readily available NO3-N and NH4-N, N mineralization, which depends Table 5. Variation in C:N ratios and potentially available nitrogen (PAN) in first year for composted and non-composted organic amendmentsz Estimated PANy Broiler litter Broiler litter ‘‘compost’’ Dairy solids Dairy solids compost Rabbit manure Rabbit manure compost Yard trimmings Yard trimmings compost WSU compost Pelleted fish Canola meal Feather meal z N (%) C:N Mean 3.84 4.05 1.62 1.99 3.00 1.80 2.00 1.72 1.70 9.4 5.66 13.7 9.5 8.8 27.0 19.8 11.5 10.0 13.3 16.5 15 4.5 8 4 42 38 9 6 27 22 19 5 7 77 60 99 Range 27
54 28
40 5
17 2 to 16 NA NA 12
28 10 to 19 NA NA NA NA Adapted from Gale et al. (2006). PAN was estimated from field studies of N uptake by corn (Zea mays L) after incorporation of the amendments into soil, with reference to standard curves of fertilizer recovery efficiency. Ranges are given for materials that were assessed at two sites (northwestern Oregon and southwestern Washington) in each of 2 years (2002 and 2003). Other materials were only tested at the two different locations in 2003. Canola and feather meals were only assessed once. y on soil temperature and moisture as well as the compound chemical structure, will also influence N availability (Hogue and Neilsen 1987). The C:N ratio is probably the most robust indicator of potential N mineralization, and recent studies of an array of organic amendments have described relationships between C:N ratios and first year N mineralization (Gale et al. 2006; Table 5). However, C:N ratio is an imperfect predictor of N mineralization (see yard trimmings compost, Table 5). Most data on mineralization of N from organic amendments, and the data summarized in Table 5, are for soil incorporated amendments and there is no similar information for surface-applied mulches. Surface-applied mulches would be expected to decompose and release N more slowly than incorporated materials, but quantitative studies comparing mineralization for incorporated and surface-applied materials are lacking. Irrigation methodology further complicates prediction of N mineralization from surface-applied materials. For example, microsprinkler irrigation, which wets the entire root-zone mulch probably results in greater N mineralization than drip irrigation, which wets only a small portion of the mulch (Neilsen et al. 2008). Supplying N from organic sources is further complicated by continued release over a number of years, as illustrated by estimates of 25, 10 and 5% mineralization of N from field-applied biosolids for years 1
3 after application, respectively (Zebarth et al. 2000). This research is cited as illustrative of the complications which can arise from accounting for multi-year N mineralization although it should be noted that use of biosolids is often prohibited in organic production systems. Inefficiencies in plant N utilization result when the seasonal pattern for N uptake does not coincide with peak N mineralization, particularly under irrigation where drainage water can leach excess root zone N. Furthermore, the narrow N:P ratio of many organic nutrient sources, particularly composts, compared with crop N:P uptake ratios results in a relative enrichment of soil with P over time and an increased risk of P-contamination of water sources (Nelson and Janke 2007). A range of mulches (Table 3) has been used due to their ability to partially control weed growth, in addition to providing the other soil benefits discussed Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. 682 CANADIAN JOURNAL OF PLANT SCIENCE previously. Weed control benefits from mulching can be extended by weed reduction via cultivation prior to planting of the perennial crop and establishment of the mulch. However, weeds inevitably begin to re-establish in organic mulches, necessitating mulch reapplication and renewed weed control. Organic materials to be used as mulches or soil amendments are often derived from bulky materials, so producers tend to use locally available organic soil amendments to reduce transportation costs. This raises the possibility of important variations in their chemical and physical properties, which will require analysis and assessment for suitability; compost made from broiler manure in the Fraser Valley will differ considerably from compost made from beef cattle manure in the Okanagan Valley. The range of organic materials compatible with crop growth requirements is more limited for blueberry than apple and grape. Conventional blueberry in British Columbia is usually mulched with about 5 cm of Douglas-fir sawdust, which provides an ideal environment for blueberry root growth, but also causes significant N immobilization and necessitates the use of supplementary high-N fertilizers. A significant challenge for organic blueberry producers is the identification of alternative mulch materials, such as composts, that do not cause extreme N immobilization but also foster root health. Blueberry is extremely sensitive to high soil electrical conductivity and pH, and grows best at soil pH between 4.5 and 5.2 (BCMAL 2006). As many composts often have relatively high pH and high EC values, their utility as mulches for organic blueberry production may be limited. Research to identify or produce types of compost with relatively lower pH and EC values, and to determine the impacts of various compost mulches on blueberry root health is warranted. The use of uncomposted manures in organic fruit production is likely to be questioned in the future by concerns about bacterial contamination of the fresh fruit products. Thus, to supply sufficient N, organic production will depend upon the use of various composts and meals (Table 3). As additional nutrient sources, several commercial liquid organics (Table 3) are available and suitable for application with irrigation water, but there have been few comparison trials of their effectiveness. As many of these materials are suspensions, they can also plug irrigation lines. Their availability and mobility in the soil relative to inorganic salts is little known. Inorganic materials are acceptable nutrient sources in organic production systems provided they are natural, unrefined and unmodified compounds (Table 3). Their nutrient content and solubility, as for rock phosphate (P) and greensand (K), can be lower than commercially available chemical fertilizers. Under BC organic regulations, inorganic fertilization is allowed providing a severe nutrient deficiency can be documented for the target crop. Vegetation Management In-row Vegetation Management Apple, grape and highbush blueberry are perennial row crops frequently requiring some degree of suppression of competing vegetation. Decreased vigour and yield of young and establishing plants resulting from excessive competition for N and water by weeds has long been recognized for apple (Hogue and Neilsen 1987) and grape (Tesic et al. 2007). The inability to use chemical herbicides to control in-row vegetation is a major constraint to achieving high yields in organic production systems (Gianessi and Reigner 2007). Widely adopted, organically acceptable methods of in-row vegetation control include repetitive mechanical or hand cultivation, particularly early in the growing season, or use of a wide range of mulch materials. Despite the development of specialized equipment to allow cultivation near trees, such as the Rineri cultivator (Edwards 1988), damage to trunks and roots of shallowrooted, densely planted apple orchards can occur. Additional limitations to mechanical cultivation include high fuel costs and degradation of soil structure (Haynes 1980). The latter concern is a significant problem, since maintaining or improving soil quality is fundamental to the philosophy of organic production. Cultivation also increases the mineralization of most organic mulch materials relative to undisturbed mulches, and once mulching is chosen as an approach to weed management, it is difficult to use cultivation as a supplementary tool without destroying the mulch. Hopes of discovering in-row cover crops that are beneficial (or non competitive) to the economic crop have often proved elusive as such crops in turn may be difficult to establish and maintain against other more competitive species. For example, the use of N-fixing white clover (Trifolium repens L.) as a cover crop augments N-nutrition of apple, but it does not eliminate a reduction in vigour and yield relative to trees maintained in weed-free herbicide strips, and is difficult to maintain due to winter dieback (Neilsen and Hogue 2000). In contrast, repetitive in-row mechanical cultivation throughout the growing season increases tree productivity relative to whole orchard floor ground cover (Neilsen and Hogue 1985). Perennial organic production systems would benefit greatly by the discovery of new cover crops or cover crop management systems that would allow for the growth of an effective non-competitive N-fixing cover crop in the row. Several lesser known techniques have been advocated for in-row weed control in organic production systems, including incineration or steaming of weeds. Limitations of these approaches include their high energy costs, potential to damage both perennial trunks and plastic irrigation lines, and relative ineffectiveness against deeprooted perennial weed species. In the dry interior of British Columbia, flaming of weeds also poses a risk of grass or forest fires. Use of acetic acid has similarly been NEILSEN ET AL. * ORGANIC FRUIT PRODUCTION IN BRITISH COLUMBIA Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. advocated as an organic herbicide, but it is expensive with unit area costs in one study ranging from 50- to 80fold higher compared with applications of the herbicide glyphosate and with less effectiveness against re-growth of perennial weeds (Young 2004). Alley Cover Crops Most perennial fruit production systems use a strip of permanent vegetation in the alleys between the fruit crop rows. In British Columbia, the alleys are usually sown initially with turfgrass mixes that are allowed to become colonized by weeds and indigenous grasses. The choice of alley cover crop is more critical for organic than for conventional systems. As with organic amendments and mulches, the provision of N is usually the primary criterion dictating the choice of alley cover crop and management system, and most organic production systems attempt to utilize N-fixing legumes as cover crops or components of cover crop mixes. The N in alley cover crops can become available to fruit crops via mycorrhizal connections (Cheng and Baumgartner 2006) and decomposition of cover crop litter resulting from mowing and the turnover of cover crop roots (Patrick et al. 2004; Cheng and Baumgartner 2006; Ovalle et al. 2008). While there is generally some growth of fruit crop roots into the alley cover crop (Morlat and Jacquet 2003; Celette et al. 2005), intentionally transporting mowed cover crop litter to the weed-free root zone of the fruit crop (‘‘mow and blow’’) can enhance acquisition of N by the fruit crop. Substantial N can be made available when alley cover crops are tilled-in as green manures (Blackshaw et al. 2005), and some fruit production systems manage alley cover crops as winter annuals planted in late summer or fall and incorporated in the spring. Tillage and reseeding of alternate alleys of perennials each year can be used to balance the provision of regular green manure N inputs with the other benefits of cover crops, such as enhancing soil organic matter, reducing erosion and providing refuge for beneficial insects. The selection of grape or apple rootstocks on the basis of their ability to acquire nutrients and water in the presence of competing vegetation would be highly beneficial to the development of organic fruit production systems. Despite opportunities to use cover crops for N supply, alley cover crops generally compete with fruit crops for water (Celette et al. 2005) and often reduce fruit yields (Bowen and Freyman 1995). Advances in the use of drip irrigation, coupled with optimal in-row vegetation management, may provide opportunities to minimize competition for water. However, the use of drip irrigation in semi-arid environments can limit the choice of alley cover crops to drought-tolerant species. The choice and management of alley cover crops can also have substantial influences on insects and diseases. While cover crops are frequently promoted for their disease suppressive effects, utilizing alley cover crops to 683 control pathogens in the rhizosphere of fruit crops is challenging. For example, most legumes grown in temperate climates are excellent hosts for root-lesion nematodes (Pratylenchus spp.) and can foster buildup of their populations (Forge et al. 2000). Similarly, the addition of fresh and high-N organic materials to soil via green manures or seed meals can temporarily increase populations of facultatively saprophytic fungal pathogens such as Pythium (Mazzola et al. 2001). Brassica cover crops (mustards, oilseed radish) are frequently promoted for suppression of plant-parasitic nematodes in vineyards. While the green manures of these crops are effective preplant biofumigants (Mazzola et al. 2002), Brassica species can, however, be good hosts for root lesion nematodes (Forge et al. 2000). Unless Brassica cover crops are effectively incorporated as green manures they might actually foster buildup of root-lesion nematode populations. Vrain et al. (1996) found that alley cover crops differ in their effects on root-lesion nematode population development, but the changes in population densities in the alleys did not appear to influence nematode population densities in the rhizosphere of the fruit crop, raspberry. In grapes, removal of alternative sources of food for climbing cutworm, particularly winter annual mustards such as Draba verna and shepherd’s purse (Capsella bursa-pastoris) before bud break is associated with greatly elevated damage to the buds of grapevines. Control of weeds in the vine rows is, therefore, not recommended until after shoots have elongated and the first basal leaves have fully expanded (Lowery 2006). Application of mulches to the vine rows will also reduce stands of these beneficial plants, but it might be possible to provide alternative cutworm attractive plants between the rows. Water Management Conservation of water resources is not a regulated activity in organic certification programs, although protection of groundwater resources is a stated goal which indirectly requires sound water management techniques in irrigated production systems (http:// www.ams.usda.gov/AMSv1.0/ http://www.agf.gov.bc. ca/organics/organics). In addition, irrigation practices potentially interact with other on-farm management such as mulching, composting, companion planting, green manuring and cover cropping which are required by organic agriculture organizations (http://www.certi fiedorganic.bc.ca/cb/soopa.php), in ways which may limit irrigation choices for organic producers. There is little documented information specifically related to water management in organic production systems, but there is a wealth of information to be derived from other horticultural production systems (Naor 2006; Lascano and Sojka 2007). This review will focus on findings from British Columbia and similar production areas in the Pacific Northwest. Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. 684 CANADIAN JOURNAL OF PLANT SCIENCE Tree fruits, wine grapes and blueberries grown in southern British Columbia are usually irrigated. The major production regions for tree fruits and wine grapes, the Okanagan, Similkameen and Creston Valleys, have a semi-arid climate with high in-season water deficits (Table 2), and are experiencing potential conflicts for water supply (Neilsen et al. 2006; Cohen et al. 2006). Production of blueberries is concentrated in the Fraser Valley, which has a maritime climate, but warm dry summers resulting in large growing season moisture deficits (Table 2). Lack of infrastructure and poor water quality provide challenges to water supply for irrigation in this region and beneficial water and nutrient management practices are crucial in preventing leaching losses to vulnerable aquifers (Wassenaar et al. 2006). Efficient water management practices are similar for both organic and conventional producers and include the use of conservative irrigation systems, irrigation scheduling to meet evaporative demand and mulches to reduce evaporation from the soil surface. For British Columbia crops, soils and climate conditions, efficient irrigation practices for both sprinkler and micro-irrigation are summarised in Van der Gulik (1989; 1999). Conservative irrigation systems including drip, microsprinklers, microspray and microjet require low water pressures to operate and wet a much smaller volume of soil than high-pressure overhead and under-canopy sprinklers, which have a lower maximum application efficiency of 75% compared with 95% for drip systems (Van der Gulik 1999). Less information is available with respect to other micro-irrigation systems, although Neilsen et al. (2008) demonstrated that small radius microsprinklers designed to wet only the planted strip in a high-density apple orchard in the Okanagan equalled drip irrigation in efficiency. Micro-irrigation systems can reduce the potential environmental impact of irrigation, through reduction in deep drainage and nutrient leaching from horticultural production systems (Gardenas et al. 2005; Neilsen at al. 2008), thus fulfilling goals for groundwater resource protection (http:// www.certifiedorganic.bc.ca/cb/soopa.php). In the Okanagan Basin, micro-irrigation is used for approximately 30% of all tree fruit and grape production (Van der Gulik and Neilsen unpublished data). It is not known what fraction of organic producers use micro-irrigation technology. Little research on irrigation practice in either organic or conventional production systems has been reported for blueberries in southern British Columbia. In the adjacent Pacific Northwest region of the United States, overhead sprinklers predominate in older plantings, but drip irrigation has been successfully adopted in newer high-density production systems with raised beds (Strik and Yarborough 2005). Scheduling irrigation to meet plant demand can potentially reduce water applications by reducing runoff from the surface, deep percolation beneath the root zone, and soil water evaporation after irrigation (Howell 1996; Allen et al. 1998). The effects of crop-specific seasonal and inter-annual canopy development, crop load and crop growth stage on water demand have been well summarized in Naor (2006) for deciduous fruit crops. In British Columbia, fully automated irrigation scheduled to meet plant demand reduced annual water applications to a high-density apple orchard in the Okanagan Basin from 1304 to 646 L per tree when compared with a constant irrigation rate (Neilsen and Neilsen 2002). Water use efficiency can be improved in organic production systems if irrigation scheduling is used to apply water according to crop requirements and detailed methodology for scheduling irrigation for British Columbia crops, soils and climates is available to producers (Van der Gulik 1989, 1999). Mulches may be used for weed control in organic production systems (as discussed earlier) and also to enhance soil aeration and drainage, particularly in high bush blueberry production (Bryla and Linderman 2007). Indirectly, mulches have been shown to enhance soil properties important for water management such as infiltration rate (Table 4). Mulches can also reduce water losses from soil evaporation by up to 30% in clay soils (Broberg 2002) and up to 50% in a sandy loam soil (Neilsen, unpublished data). In general, the increased water use efficiency associated with micro-irrigation is beneficial, but limitations to production may occur in some cropping/irrigation system combinations. In organic production systems, nutrients can be applied as broadcast, composted amendments. Point source applications of water through drip systems may fail to wet the surface soil and compost thus reducing downward movement and availability of nutrients into the root zone compared with small-radius micro-sprinklers (Neilsen et al. 2008). Irrigation management may also affect disease susceptibility. In a fine-textured soil, highbush blueberries grown on raised beds amended with sawdust developed severe root rot under drip irrigation, which was attributed to localized soil saturation close to the crown (Bryla and Linderman 2007). Blueberries grown with overhead sprinklers and micro-spray irrigation were not similarly affected. Reducing the total amount of water applied also reduced disease. Thus in both conventional and organic production systems, it is important to match irrigation system type and management to achieve both production and environmental protection goals. More research is required to develop beneficial irrigation management for the specific requirements of organic production systems. ORGANIC PLANT PROTECTION As protecting plants from pests using organically acceptable methods involves understanding the unique relationship between each pest and the specific crop, this section is organized by crop. NEILSEN ET AL. * ORGANIC FRUIT PRODUCTION IN BRITISH COLUMBIA Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. Insect Management Apple As in most apple growing regions, codling moth (Cydia pomonella L.) is the key insect pest of apple in British Columbia with no significant natural biological controls or plant resistance. Since 1992, a collaborative project among the British Columbia Fruit Grower’s Association and Regional District governments has maintained efforts to control codling moth populations via a Sterile Insect Release (SIR) Program (Dyck and Gardiner 1992). Although not specifically designed for organic growers, this program has facilitated an expansion of organic production in BC. Currently the SIR program is the cornerstone of a successful area-wide integrated pest management program incorporating many organically acceptable technologies (Thistlewood and Judd 2003). These include pheromone-based mating disruption of codling moth via Isomate, codling moth larvae capture using larval aggregation pheromones (Judd and Gardiner 2005) or codling moth population reduction via weekly sprays of granulosis virus (Cossentine and Jensen 2004). Entomopathogenic nematodes can also be used to control overwintering codling moth larvae (Lacey et al. 2006a), with efficacy being greater with organic mulch than with bare soil (Lacey et al. 2006b). Leafroll caterpillar (Lepidoptera: Tortricidae) larvae can be controlled with the organic microbial pesticide Bacillus thuringiensis Berliner (Bt) (Cossentine et al. 2003). A multiple species mating disruption dispenser is formulated to include all six tortricid species found in British Columbia (Judd and Gardiner 2004). Control of the tentiform leaf miner [Phyllonorycter mespilella (Hubner)] and apple ermine moth (Yponomeuta malnellus Zeller) is achieved using parasitoids, the latter pest by the European species Ageniaspis fuscicollis Dalman (Hymenoptera: Encrytidae) (Cossentine and Jensen 1994; Cossentine and Kuhlmann 2001). Grapes The western grape leafhopper (Erythroneura elegantula Osborn) and Virginia creeper leafhopper (E. ziczac Walsh) are major pests of grapes grown in the interior of British Columbia (Lowery 2006; Lowery and Judd 2007). Several non-chemical methods of control have recently been investigated, including the application of yellow sticky tape (10.2 cm width) under the vine cordon in spring, which reduce numbers of leafhopper eggs and nymphs by 96 and 92%, respectively, when applied to every row (Lowery, unpublished data). Purchasing and applying the tape is costly, but it can be effectively used on outside rows where leafhoppers overwinter in bushes and debris adjacent to vineyards. Suppression of leafhopper populations is also achievable by early-season removal of basal leaves. Growers often remove leaves around the fruiting clusters later in the season to reduce the incidence of bunch rot and improve fruit quality. Removal of these basal leaves around the middle of June 685 when most first-generation leafhopper eggs have been deposited lowers the incidence and severity of grape diseases (Sholberg et al. 2008) and also reduces leafhopper numbers (Lowery 2006). As for most perennial crops, properly balanced nutrition and an adequate supply of water to support healthy vine growth influence the degree of damage from insects and diseases. Vigour depends partly on the rootstock, but is also governed by pruning, cropping levels, selection and management of appropriate groundcover vegetation, and provision of nutrients and water. Most pests of grapes, particularly leafhoppers and mealybug, are more abundant on overly vigorous vines that provide better nutrition and a darker, more sheltered environment (Lowery 2006). Deficit irrigation from berry set to veraison reduces leafhopper numbers more than 60% with only a modest reduction in yield, which is offset by smaller berries that produce higher-quality wine (Dry et al. 2001). At the other extreme, chlorotic vines of low vigour are less able to tolerate insect damage and are more prone to attack by hard scale and wood boring beetles (Lowery 2006). Tiny parasitic wasps of the genus Anagrus (Hymenoptera: Mymaridae) that develop in the eggs of leafhoppers can effectively control numbers of these pests in many vineyards. Anagrus erythroneurae Triapitzyn and Chiappini provide effective control of the western grape leafhopper and limit the range of this pest in the Okanagan Valley (Lowery et al. 2007). Anagrus daanei Triapitsyn, which parasitizes eggs of the Virginia creeper leafhopper, has fewer over-wintering hosts and, consequently, provides less than adequate control of this species. Future research could involve methods to enhance populations of A. daanei, possibly by providing suitable over-wintering or early-spring hosts. A third species, A. tretiakovae Soyka, which contributes to the control of both leafhopper species in eastern North America, Washington and California, is absent from British Columbia and could be considered for importation (Lowery et al. 2007). The lack of pesticides approved for use in certified organic vineyards has been a major obstacle to greater adoption of organic grape production in British Columbia. Until recently, the only organically acceptable spray material previously available to control insect pests on grapes in British Columbia was insecticidal soap. As a result of regulatory changes and greater chemical company support, several OMRI-approved (Organic Materials Review Institute, Eugene, OR) pesticides have recently received registration or are in the process of being registered for use on tree fruits and grapes in Canada. Registrations include the clay-based particle film SurroundTM for suppression of leafhopper populations and Bt (DipelTM) for leafrollers and snailcase bagworm. Other organic insecticides for grape under evaluation in the Minor Use Program (AAFC) include highly refined summer oils for the management of leafhoppers, thrips and spider mites, commercial Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. 686 CANADIAN JOURNAL OF PLANT SCIENCE extracts from the Indian neem tree [Azadirachta indica (A. Juss.)], for control of leafhoppers and thrips, and spinosad (EntrustTM) for climbing cutworm. Future registration of these and other approved organic materials will facilitate organic fruit production in British Columbia. Surveys of commercial vineyards indicate that cultivation of alleys and removal of weeds in vine rows early in spring are associated with greater cutworm damage (Lowery 2006). In particular, feeding of cutworm larvae on the buds of grapevines is greatly reduced when winter annual mustards such as Draba verna L. and shepherd’s purse [Capsella bursa-pastoris (L.)] were present in the vine rows. Research is currently underway at AAFC Summerland to evaluate the use of mustards to control cutworm damage in the hope that these pests can be controlled by non-chemical means. Diversification of groundcover vegetation and inclusion of flowering plants that provide nectar and alternate prey species can also enhance numbers of beneficial insects and predatory mites that help maintain numbers of pests below damaging levels (Andow 1991; Hokkanen 1991). Trap cropping techniques such as these may be particularly important for the organic sector, as natural enemies are more abundant in mixed plantings compared with monocultures (Andow 1991). Blueberry Management of insect pests is currently not a major impediment to organic blueberry culture in British Columbia. The blueberry maggot (Rhagoletis mendax Curran), the most serious pest of blueberry, is absent from British Columbia. Although not always of economic importance, blueberries in British Columbia are attacked by a complex of lepidopteran larvae (leafrollers, spanworm, wintermoth, tent caterpillars). Other pests include European fruit lecanium scale [Parthenolecanium corni (Bouché)] and the aphid [Ericaphis fimbriata (Richards)] (BCMAL 2007). Aphids are primarily damaging to blueberry because of their ability to transmit diseases (Rugen and Bachman 2008) including blueberry scorch virus (Raworth 2004), but it is generally accepted that aphicides do not reduce the spread of aphid-borne non-persistent plant viruses (Simmons 1982). Non-colonizing aphid species are able to spread viruses such as blueberry scorch following very short feeds lasting only several seconds to less than a minute. Insecticides do not act quickly enough to prevent disease transmission (Robert 1992). Where insects are likely to pose a problem on blueberry, a dormant oil spray can help control the overwintering eggs of aphids and moths (BCMAL 2007). Control of scale during the dormant period requires the addition of lime sulphur to the oil spray. Branches infested with tent caterpillar nests or heavily infested with scale can be pruned out, and sprays of the naturally occurring bacteria Bt are recommended when leafroller caterpillars are numerous (BCMAL 2007). These sprays will also help control caterpillars of other species attacking blueberry. Irregardless of the crop, control of insect pests is best achieved with a hierarchical approach that begins with improved soil quality and proper plant nutrition. Planting suitable cultivars and rootstocks, when available, and employing various cultural and physical control practices will reduce the reliance on chemical sprays. When monitoring of pest populations indicates that sprays are required, an expanding list of OMRIapproved materials is available to prevent economic losses. In support of this more holistic approach to pest management, a greater research effort is required to provide a better understanding of the agro-ecosystem and the biotic and abiotic factors that help control pest populations. Above-ground Disease Management Apple The semi-arid climate in the major apple growing regions of interior British Columbia reduces the occurrence of plant diseases. Major above ground diseases are limited to fire blight [Erwinia amylovora (Burrill) Winslow et al.], powdery mildew [Uncinula necator (Schw.) Burr] and the post-harvest blue (Penicillium expansum Link ex. Thom) and grey (Botrytis cineria Pers.Fr.) molds. Apple scab [Venturia inaequalis (Cooke) Winter], a major limitation to organic production in humid regions, does not occur in all British Columbia districts or in all years. Disease control in organic orchards is generally limited to crop manipulation to reduce disease outbreak, or application of approved organic materials (Weibel and Hăselli 2003). For example, improved orchard sanitation via removal of infected sources can restrict mildew and scab impact, and avoidance of excessive tree vigour can reduce scab and fireblight incidence. In British Columbia, there has been some success in reducing postharvest apple molds under laboratory conditions using naturally occurring Bacillus spp.(Sholberg et al. 1995) and an isolate of Pseudomonas fluorescens (Etebarian et al. 2005), but these antagonists have not been registered for field use. Improved disease pathogen identification is helpful in organic orchards as indicated recently by development of a macroarray technique to forecast apple scab, powdery mildew and fire blight (Sholberg et al. 2005). Grape The arid conditions of south central British Columbia also limit the incidence and severity of foliar diseases of grapevines, resulting in a need for few fungicide applications. Downy mildew [Plasmopara viticola (Berk. & Curt.) Berl. & de Toni] is not present, but powdery mildew reduces vine growth and can severely reduce fruit quality. A very low rate of fruit infection can taint the fruit and lead to outright rejection by the winery Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. NEILSEN ET AL. * ORGANIC FRUIT PRODUCTION IN BRITISH COLUMBIA (BCMAL 2006). Control of powdery mildew in organic vineyards in British Columbia traditionally depended on periodic applications of sulphur sprays, but the OMRI-approved fungicides potassium bicarbonate (MilStopTM) and SerenadeTM, derived from the soil micro-organism Bacillus subtilis, recently received registration. Serenade is also registered for the control of sour rot of grapes. The severity of powdery mildew can also be reduced somewhat by opening up the canopy to improve air circulation and light penetration (Sholberg et al. 2008). Irrigation should be applied under the vine to reduce leaf wetting, and nutrients and water should be managed carefully to avoid excessive vigour that leads to dense canopies. Botrytis bunch rot of grapes, caused by Botrytis cinerea, causes significant losses to the British Columbia grape industry, as it does in all grape-producing areas worldwide. Although control is largely achieved with fungicides in conventional plantings, cultural management methods, such as leaf removal, hedging, and shoot positioning, play an important role (Sholberg 2004). Removal and destruction of infected fruit will reduce damage, but this practice is time consuming and expensive. Growers often remove leaves around the fruiting clusters prior to veraison by hand or with a leaf pulling machine to help reduce infection rates and improve fruit quality. Removal of basal leaves early in the season around mid-June when most first generation leafhopper eggs have been deposited on the older leaves lowers the incidence and severity of bunch rot (Sholberg et al. 2008). Fruit quality appeared to improve slightly, but additional research is required to determine if this translates into higher-quality wine. Altering the timing of leaf removal does not increase costs for growers who utilize this cultural management practice later in the season, but early removal of leaves provides superior levels of disease control. Blueberry The most significant above-ground diseases of blueberry in British Columbia include botrytis fruit rot and blight (Botrytis cinerea), mummy berry [Monilinia vacciniicorymbosi (Reade) Honey] and bacterial blight (Pseudomona syringae pv. syringae). Blueberry scorch virus is also extremely important to organic blueberry growers. Key management options for blueberry scorch include planting of virus-tested stock, and rapid diagnosis and removal of infected plants to prevent spread within a field. The virus is spread by aphids, and other management options centre on aphid management. Botrytis blight causes significant losses of fruit if wet weather occurs during bloom, fruit ripening or harvest. Cultural practices that can reduce losses to botrytis blight include selective pruning to remove infected twigs and improve airflow within the canopy, and avoidance of excessive levels of nitrogen that promotes excessive leaf growth (BCMAL 2006). The biological fungicide 687 SerenadeTM is effective at reducing botrytis diseases and is registered for control of botrytis blight on blueberry in Canada. Repeated raking of mulch, and light tillage of soil between rows in the spring, can reduce primary inoculum of mummy berry by disrupting formation of apothecia. Burying of mummies via raking of mulch may also enhance winter mortality of mummies, but this has not been documented. Mummy berry spores require free water for germination and infection, and pruning to enhance canopy air circulation is also believed to help reduce disease pressure. Research in Georgia (Scherm et al. 2004) indicates that SerenadeTM, is effective against mummy berry, but it is not registered for this use in Canada. Wettable sulphur sprays can also be used to reduce both botrytis blight and mummy berry (Rugen and Bachman 2008). Cultural control practices for bacterial blight include pruning and destruction of diseased wood. Two biological control products, BlightBanTM (Pseudomonas fluorescens) and SerenadeTM, have both been shown to be effective at reducing bacterial blight. While both are OMRI certified in the United States, they are not registered for control of bacterial blight of blueberry in Canada. Blueberries are unique among commercially produced fruit crops in their requirement for acidic soils and preference for nitrogen in the form of ammonium. Excess N can result in greater amounts of diseases such as bacterial blight (Sanchez and Demchak 2004; BCMAL 2006; Rugen and Bachman 2008). Below-ground Disease Management All perennial fruit crops are prone to root diseases. Earlier portions of this paper explored how organic practices can influence the activity of root pathogens in established plantings. For perennial fruit crops, controlling root pathogens before replanting ensures rapid establishment and high early yields, which can translate into substantial economic benefits. Accordingly, the development of both conventional and organic-compatible root disease management options has been focused primarily on pre-plant interventions. Apple The apple replant disease syndrome is the result of several root pathogens, usually acting in combination. The pathogens of significance to apple seedlings include Rhizoctonia spp., Pythium spp., Phytophthora spp., Cylindrocarpon spp. and root-lesion nematodes (Mazzola 1998). Brassica green manures can be used for preplant control of a variety of soil-borne pathogens, including root-lesion and root-knot nematodes, Rhizoctonia and Pythium. Mazzola and co-workers (2001, 2002, 2005) have used canola seed meal as a plantinghole amendment for possible preplant control of apple replant disease. A variety of high-nitrogen amendments (e.g., manure slurries, biosolids, seafood wastes) have also been used as biofumigants for preplant site 688 CANADIAN JOURNAL OF PLANT SCIENCE Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. preparation (Bailey and Lazarovits 2003). Pathogen reduction after application of such high-N amendments appears to result from localized liberation of ammonia or nitrous acid, both of which are toxic to many soilborne plant pathogens (Tenuta and Lazarovits 2002). Root-lesion nematodes in apple have also been suppressed by preplant inoculation with mycorrhizal fungi (Forge et al. 2001). Grape In cool climate grape-growing regions such as British Columbia, ring nematodes are likely the most damaging species (Pinkerton et al. 2004). Although the pathogenicity of root-lesion nematodes to grape is currently unclear (Ramsdell et al. 1996), they are widespread in Okanagan vineyards and may be important determinants of root health. Cylindrocarpon macrodidymum Halleen, Schroers, & Crous cause black foot disease in California (Petit and Gubler 2006) and may be associated with root and crown disease in British Columbia. Pythium ultimum is associated with root and crown diseases in British Columbia and is also associated with necrosis and the decline of grapevines in British Columbia (Utkhede and Vielvoye 1984). Blueberry Root rot and decline of highbush blueberry has become a more prominent problem in British Columbia. Phytophthora cinnamomi Rands has been identified as a causal agent (Forge et al. 2007), but other Phytophthora species and perhaps the nematode Paratrichodorus renifer Siddiqi may be involved in the syndrome and are the subject of ongoing research (Forge et al. 2007). Current organic-compatible recommendations for reducing the incidence of root rot include improving field drainage, planting into hills, and avoiding excessive irrigation around the plant crowns. RESEARCH NEEDS Central to the philosophy of organic production of crops is the concept of maintenance of a regenerative agricultural production system with minimal environmental impact. Such a philosophy implies a need to undertake systems research to assess cost-to-benefit ratios when developing acceptable management strategies. With the exception of research by Reganold et al. (2001) on apples there have been few comprehensive systems studies published on organic fruit production. Given the perennial growth habit of fruit crops, an increase in long-term, integrated, multi-factor studies is a priority. For example, the use of crop resources including mulches, amendments and cover crops can simultaneously affect nutrition, water availability and insect and disease progression thus necessitating an ecosystem perspective. Nevertheless important research issues have already been identified by more narrowly focused research studies. It will be important to maintain adequate N supplies given the current imprecise knowledge of N release for production systems receiving organic rather than commercial fertilizers. Little is known of the temporal dynamics of N release from surface-applied as opposed to incorporated amendments. There is also a need for research on the sustainability of N management strategies, which, in the short-term, can result in plants with lower N concentrations, reduced attractiveness to aphids and improved red colour (apples). Reliance on composts and other organic amendments as primary sources of N can result in soil P enrichment, changes in soil pH and imbalances in other nutrients. Nutrient availability from some organically suitable sources such as liquid organic extracts are little understood despite their potential to be efficiently applied to the root zone with irrigation water. A range of organic soil management practices are available that fulfill the desired criteria of conserving and even augmenting soil organic matter content and increasing soil microbial activity and diversity. Less has been documented concerning the quantitative relationship between these improvements in soil quality and plant performance. There is a need to identify novel cover crops which might achieve an acceptable balance between detrimental competition and beneficial soil health improvement and inhibition of insects and diseases. To enhance beneficial insect populations, flowering ground cover crops could be sought that act as alternate hosts. Legume cover crops can supply N to the economic crop, but the long-term repercussions associated with the build-up of soil-borne pathogens are not known. It is also important to research organically acceptable soil disinfestation methods that are not restricted to use prior to the establishment of plantings or require treated fields to be out of production for extended periods. These could include biofumigant cover crops that have commercial value or can be utilized over winter (fallspring) resulting in organically acceptable methods for control of soil-borne pests that can also be used on established plantings. Current weed control methods accepted for organic production include mechanical cultivation and the use of black plastic mulching, which have limitations associated with high energy costs and degradation of soil structure. Increased research to develop more effective weed management strategies is a priority, especially for new plantings which are more sensitive to excessive weed competition than established crops. Similarly, there are research needs associated with the development of mulches specifically designed for organic production, which are suppressive to the development of insects, diseases and weeds. Water management is often ignored for special consideration in organic production systems despite the almost universal irrigation of apple, grape and blueberry in British Columbia. Few research studies have been published on irrigation specific to organic Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF NEWCASTLE on 06/12/20 For personal use only. NEILSEN ET AL. * ORGANIC FRUIT PRODUCTION IN BRITISH COLUMBIA production systems. Research is thus needed on the effects of irrigation systems on disease prevalence (and control), since irrigation increases humidity and the duration of soil saturation. Optimizing irrigation scheduling to reduce undesirable nutrient leaching losses from organically amended soils needs to be assessed relative to conventionally fertilized soils. Micro-irrigation systems, such as drip irrigation, are likely to be viewed as environmentally desirable in the future from the water conservation view point, but such systems pose unique challenges for organic production. For example, how does micro-irrigation affect mineralization of organic amendments and the spatial distribution and availability of nutrients, and what are the implications of between-row high biomass cover crops or use of native cover crop species in semi-arid regions? Many of the previously identified research needs are applicable for all of the fruit crops assessed in this review. However, the unique associations between crop, insect and disease interactions means there will be cropspecific research requirements for organic plant protection strategies. A prerequisite for this research will be a better understanding of pest biology and their natural control agents which was not emphasized when depending solely on chemical control methods. For apple, the existence of the SIR-program for conventional growers in the interior valleys creates the potential for developing an organic-friendly area-wide control program with its associated research needs. Overcoming replant disorder without the use of soil sterilants is especially important for apple, but may become more important for grape and blueberry as these sectors mature. Postharvest disease issues are important for apples, which can be stored for long periods. There are a number of microbial biocontrol agents which have worked well to control post-harvest molds under controlled laboratory conditions, but more research is needed in the field. For grape, there is promising research to control leafhoppers, bunch rot and mildew by cultural methods, but more research is required to assess the effectiveness of controls under extreme pressures and to assess the consequences for wine quality. There is currently too much reliance on the use of sulphur and copper to combat foliar diseases of all three crops. Thus, in common with most fruit crops, research on alternatives and accelerated field assessment and approval of acceptable organic pesticides is a priority. Integrated assessment of cover crops for insect, disease and nutritional consequences is particularly important for grapes which have only recently abandoned a strategy in British Columbia of clean cultivation of the whole vineyard floor. Blueberry has the lowest proportion of organic production of the three fruit crops in British Columbia. Consequently, there has been little organicspecific research for blueberry. Many cultural methods have been recommended for the control of insects and diseases, but documented research is sparse, and few organic pesticides have been assessed and registered for 689 blueberry. Blueberry has special environmental requirements associated with its ability to thrive at low soil pH and sensitivity to water stress, suggesting the possibility of research to design improved mulches specific to blueberry. In general, there is no shortage of potential research projects to facilitate organic fruit production in British Columbia. Historically, organic production has received much less funding from public and private sources for research than conventional production. There are encouraging signs of changes in Canada given the recent formation of the Organic Agricultural Centre for Canada (http://www.oacc.info) with the potential for stimulating research on organic production. Focusing on the most critical research issues will be a challenge given the history of minimal research and crop and climate diversity. Currently, organic growers have computer access to a growing network of institutional web sites dedicated to summarizing current understanding and experiences with organic production. The challenge of distinguishing traditional beliefs from scientifically verified information does not decrease as information sources increase. It is important to overcome these problems and accelerate research on organic production systems to satisfy consumer demand. A greater emphasis on food, health and safety by consumers will increase demand for food products free from chemical and microbiological contaminants and enriched in beneficial nutrients, vitamins and antioxidants. Concerns for increased security of the food supply in a world characterized by uncertain cost and availability of food will further increase interest in locally produced high-quality fruits produced organically. Allen, R. G., Pereira, L. S., Raes, D. and Smith, M. 1998. Crop evapotranspiration. 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586. Bailey, K. L. and Lazarovits, G. 2003. Suppressing soil-borne diseases with residue management and organic amendments. Soil Tillage Res. 72: 169
180. Blackshaw, R. E., Moyer, J. R. and Huang, H. C. 2005. Beneficial effects of cover crops on soil health and crop management. Recent Res. Devel. Soil Sci. 1: 15
35. Bowen. P. and Freyman, S. 1995. Ground covers affect raspberry yield, photosynthesis, and nitrogen nutrition of primocane. HortScience 30: 238
241. Bristow, P. R. and Moore, L. W. 1995. Bacterial canker. Pages 49
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