Apple replant disease (ARD) is incited by a complex of causal agents including various fungi, oomycetes, and plant parasitic nematodes. These causal agents can differ significantly in abundance between orchard sites within a geographic region. Knowledge of the specific etiology of ARD is required in order to develop commercially viable soil management strategies to combat specific/individual components of the pathogen complex. In this study, we analyzed soil from six ARD affected orchard sites to assess the presence and composition of fungal, bacterial and oomycetes communities, as well as the prevalence of plant parasitic nematodes. Five fungal, and 17 bacterial classes were differentially represented in the soil microbiomes across the different locations. Mortierellomycetes was the most abundant fungal taxa represented followed by Sordariomycetes. Mortierella exigua, a fungal endophyte, was the most abundant fungal amplicon sequence variant (ASV) in the core microbiome. Among bacteria, Proteobacteria was the most prevalent phylum identified in these orchard soils. Several potential phytopathogenic fungi associated with ARD, as well as endophytes including Fusarium oxysporum, F. solani, Nectria ramulariae, Ilyonectria robusta and Nectriaceae, were identified in ARD soils. Among oomycetes, Pythium attrantheridium (Globisporangium attrantheridium), and P. irregulare (Globisporangium irregulare) were the most abundant taxa. Additionally, six different groups of plant-parasitic nematodes were found across the ARD orchard soils. Root-lesion nematodes, Pratylenchus spp., which are commonly associated with ARD, were identified in all orchard soils at population densities range from 12 to 33/100 cm3 soil. This research enhances our understanding of the ARD pathogen complex and provide important insights for developing alternative disease management strategies in the apple industry.

Apple replant disease (ARD) is a complex issue caused by various fungal, oomycetes pathogens and parasites which can differ in their abundance between sites within a geographic region. Knowledge of the specific etiology of ARD at a particular site is required in order to develop commercially viable soil management strategies to combat specific/individual components of the disease. In this study we analyzed the soil from six ARD sites for the presence of fungal, bacterial and oomycetes communities and plant parasitic nematodes. Five fungal, and 17 bacterial classes were differentially represented in the microbiomes from different locations. Mortierellomycetes was the most abundant fungal taxa represented followed by Sordariomycetes. Mortierella exigua a fungal endophyte was the most abundant fungal amplicon sequence variant (ASV) in the core microbiome. Proteobacteria was the most prevalent phylum identified in orchard soils. Several potential phytopathogenic fungi involved in ARD and endophytes including Fusarium oxysporum, F. solani, Nectria ramulariae, Ilyonectria robusta and Nectriaceae were identfied in the orchard soil. Pythium attrantheridium (Globisporangium attrantheridium), P. monospermum and P. ultimum (Globisporangium ultimum) were the most abundant oomycete taxa identified in these soil samples. Six different groups of plant-parasitic nematodes were found across the six orchards soil. Root-lesion nematodes, Pratylenchus spp., which are commonly associated with ARD, were identified in all orchards soil at population densities ranging from 12 to 33/100 cm3 soil. This research contributes valuable understanding of the ARD complex as the apple industry needs alternative approaches to combat the disease.

Farmers hoping to manage cropping systems sustainably are turning to cover crops to help mitigate plant pathogens. Plants with biofumigant properties are used to control soil-borne pathogens in agricultural settings, especially in till systems, where the brassicas are incorporated into the soil as green manure or seed meal. The effect of these crops is not well studied in no-till systems; thus, it is hard to know if they are as effective as green manure. Whether or not these cover crops can effect changes during a single growth season has not yet been studied. This study compared the response of the soil microbial community to four different brassica cover crops, two of which are commonly used in vineyards (Sinapis alba L. (white mustard) and Raphanus sativus (L.) Domin (tillage radish)) as well as two brassicas that are native or naturalized to the Okanagan (Capsella bursa-pastoris (L.) Medik. (Shepherd’s purse) and Boechera holboelli (Hornem.) Á. Löve and D. Löve (Holbøll’s rockcress)). Cover crops did not affect fungal species richness, but B. holboelli recover crops were associated with increased evenness among fungal taxa. Both C. bursa-pastoris and S. alba had lower levels of plant parasitic nematodes compared to non-brassica controls. These results were apparent only after a single growing season, which indicates growers could use this approach as needed, minimizing long-term exposure to biofumigants for beneficial soil microbes.

Abstract Plant parasitic nematodes are a constraint to the production of wine grapes worldwide. In the Pacific Northwest (PNW) of North America, including British Columbia (BC) in Canada and Oregon (OR) and Washington (WA) in the United States, the impact of plant parasitic nematodes, specifically ectoparasitic nematodes, on wine grape production has not been extensively studied or documented. This chapter discusses the economic importance, geographical distribution, host range, damage symptoms, biology and life cycle, interactions with other nematodes and pathogens, and recommended integrated management of Mesocriconema xenoplax and Xiphinema americanum infesting grapes in North America. Future research requirements and future developments are also mentioned.

There is a need to improve raspberry crop nitrogen (N) management practices, particularly when grown over aquifers vulnerable to nitrate (NO3) leaching. This study quantified the effects of N, irrigation and alley management strategies on berry yield, indices of crop vigor and N status, growing season soil N dynamics, and root-lesion nematode (RLN) population dynamics under red raspberry production in British Columbia, Canada. Conventional management (100 kg N ha(-1) surface broadcast on the row, clean cultivation of alleys, and drip irrigation for a fixed duration regardless of evapotranspiration [ET]) was compared with different mineral fertilizer N rates, application of N as manure, seeding the alley to either a perennial forage grass (perennial ryegrass [Lolium perenne L.] and 'Bridgeport II' chewings fescue [Festuca rubra subsp. commutate]) or an autumn-seeded spring barley crop, or ET-scheduled irrigation. In addition, the combination of ET-scheduled irrigation plus fertigation of a reduced rate of N was compared with conventional practices at a reduced N rate. There was little or no crop response to N source and rate, a finding attributed primarily to high nonmanaged N inputs, and possibly also to RLNs present at population densities (grand mean = 4 per cm(3) soil) expected to suppress raspberry growth. ET-scheduled irrigation reduced water use similar to 50% compared with fixed-duration irrigation without compromising crop performance. The perennial forage grass in the alley reduced soil mineral N but not yield. Taken together, these findings demonstrate that more environmentally sustainable raspberry production can be achieved through integrated management systems even in soils vulnerable to NO3 leaching.

Blueberry (Vaccinium spp.) is a rapidly growing segment of the agricultural sectors in the Pacific North-west (PNW) of the USA and Canada. Plant-parasitic nematodes are commonly found in blueberry production fields, with root lesion nematodes (Pratylenchus species) reported as being widespread; however, the identity of these populations associated with blueberry roots has not been previously determined. Eleven blueberry production fields were sampled in 2009 and blueberry and weed roots and associated soil samples were collected in the spring and autumn to quantify and molecularly identify Pratylenchus species. The dominant species found in blueberry roots and associated soil was Pratylenchus crenatus. Across seasons, P. crenatus was recovered from 47 and 53% of blueberry root samples, at mean population densities of 66 and 50 nematodes/g root in spring and autumn, respectively. Several weed species were also identified for the first time as hosts for P. crenatus. These included Bellis perennis, Bromis sp., Calystegia sepium, Capsella bursa-pastoris, Cynodon dactylon, Echinochloa crus-galli, Epilobium angustifolium, Hypochaeris radicata, Polygonum lapathifolium, Sencio sp., Sonchus sp., Taraxacum officinale and Trifolium sp. In addition, Epilobium angustifolium, Senecio sp., and Trifolium sp. were excellent hosts for P. crenatus with > 6000 nematodes/g root. Our results demonstrate that P. crenatus is the primary root lesion nematode species present on blueberry in the PNW and that many of the weeds found in blueberry fields are also hosts for this nematode. The effect of P. crenatus on blueberry health and productivity remains to be determined.

Uncertain water supplies resulting from changing climatic conditions in western North America led to this investigation of the role of crop load reduction in maintaining performance of high-density ‘Ambrosia’ apple (Malus ×domestica) on M.9 rootstock. A split-plot experimental design was imposed for three growing seasons (2007–09) with six replicates of four main plot irrigation treatments and three crop load subplots comprised of three trees. Four season-long irrigation (Irr) treatments were applied through 2 × 4 L·h−1 drip emitters per tree and included Irr1) control [100% evapotranspiration (ET) replacement], Irr2) 50% ET replacement, Irr3) 50% ET replacement to half the emitters, and Irr4) an increasingly severe treatment commencing at 50% ET replacement (once every 2 days) in 2007 and progressing to 25% and 18% ET replacement, 2008–09. Three target crop loads were established annually, 4–5 weeks after bloom as low (2.5, 3, and 3.75), medium (4.5, 6, and 7.5), and high (9, 12, and 15) fruit/cm2 trunk cross-sectional area (TCSA) 2007–09, respectively, by hand thinning around 4 weeks after bloom. Volumetric soil moisture contents generally reflected the amount of water applied and ranged from 20% for control (Irr1) to <10% for Irr4. Both irrigation and crop load treatments affected midday stem water potential more than leaf photosynthesis and stomatal conductance (gS). By the 2nd and 3rd year stem potential values for irrigation treatments ranged from a maximum of −1.0 to −1.3 MPa for Irr1 to minimums ≤-2.0 MPa for Irr4. gS decreased as midday stem potential decreased, but at any given stem potential value was greater at high crop loads, presumably in response to an increased demand for photosynthates. Fruit size decreased as crop load increased, but as irrigation deficits became more severe, fruit size was more closely correlated with stem water potential than gS. Consequently, fruit size was controlled by two mechanisms, competition for photosynthates and the effects of plant water status on gS. Negative linear relationships between crop load and average fruit size were used to determine the crop load required to produce an average fruit size of 200 g at different irrigation deficits. It was not possible to achieve adequate fruit size when applications were very low, as at 18% to 25% ET in Irr4. Crop load reduction around mid-June had no negative consequences for fruit quality, enhancing fruit color, and soluble solids concentration (SSC) and did not affect the incidence of sunburn, internal breakdown or bitter pit at harvest.

Raspberry fields in the Pacific Northwest, USA and British Columbia, Canada are often prepared for replanting by fumigating with broad-spectrum biocides to control root-lesion nematodes, Pratylenchus penetrans. Nematode-suppressive organic amendments have been advocated as reduced risk alternatives to fumigation but may pose other risks to the environment. This study compared alternative pre-plant soil management practices with respect to their effects on plant-parasitic nematode populations, soil quality parameters and risk of nitrate leaching. In fall of 2009 and 2010, a mature raspberry field was mowed down and plowed, and replicate plots were randomly allocated to each of six treatments: (1) a non-amendedcontrol, (2) fumigation with Basamido, (3) fall seeded barley cover crop, (4) recommended rate (20 m(3) ha(-1)) and (5) historical "biofumigant" high rate (250 m(3) ha(-1)) of spring incorporated poultry manure, and (6) spring incorporated compost (250 m(3) ha(-1)). Raspberry cv Saanich was planted approximately one month after incorporation of amendments. Composite soil samples were taken from each plot at multiple times during two subsequent growing seasons and analyzed for nematode populations and soil chemical and physical properties. Primocane biomass was assessed at the end of each of the first two growing seasons as an index of crop vigor. The high poultry manure and compost treatments suppressed root-lesion nematode populations nearly as well as fumigation over two growing seasons. These treatments also improved soil bulk densities and aggregation relative to control, cover crop and fumigation treatments, while compost addition beneficially increased soil pH, CEC and Ca concentrations more than manure. Primocane production in the manure and compost treatments was greater than in the control and cover crop treatments, but less than in the fumigated treatment. Substantial nitrate accumulation in soil amended with the high rate of manure indicated that application of sufficient manure to suppress parasitic nematodes would pose a significant risk of nitrate leaching. In contrast, soil nitrate accumulation was not significantly increased in the compost amended plots. Overall, compost application reduced nematode populations, improved crop growth and did not increase the risk of nitrate leaching in the short term and may be a viable alternative to fumigation. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.