Arboriculture & Urban Forestry 47(4): July 2021 2010). There is also scientific evidence showing that enhancing Ca concentrations in leaf, stem, and root tissue of plants with calcium fertilisers can reduce the severity of symptoms caused by several pathogenic fungi and bacteria (Springer et al. 2007; Percival and Haynes 2009). Pertinent examples include Erwinia carotovora subsp. amylovora, Phoma exigua (gan- grene), Fusarium solani, Botrytis cinerea and Neo- nectria galligena of apple, Monilinia fructicola (brown rot of peach), Venturia pirina (pear scab), and Guignardia leaf blotch (Bain et al. 1996; Ippolito et al. 2005; Elmer et al. 2006; Khalifa et al. 2009). Likewise, silicon (Si) fertiliser soil amendments and foliar sprays have proved effective in controlling pathogens of several plant species, including rice blast (Magnaporthe grisea, anamorph = Pyricularia grisea), grey leaf spot, pear scab (V. pirini), powdery mildew, Rhizoctonia solani, Pythium aphanidermatum, and Sclerotinia homoeocarpa (Hamel and Heckman 2000; Saigusa et al. 2000; Rondeau 2001; Uriarte et al. 2004; Wang et al. 2017; Percival 2018). While the use of Ca and Si fertilisers alone to reduce disease severity has been studied, the Ca and Si fertilisers used in this study have received limited investigation. Similarly, the potential of Ca and Si fertilisers in com- bination with a synthetic fungicide to manage scab diseases of trees has received little, if any, investiga- tion. Consequently, the purpose of these studies was, firstly, to investigate the association of Ca and Si fer- tilisers, singly and in combination with a synthetic fungicide (penconazole), as scab and leaf blotch protec- tive compounds using container-grown and field-planted species of horse chestnut (Aesculus hippocastanum) and apple (Malus domestica cv. ‘Golden Delicious’), known to be sensitive to Guignardia leaf blotch and apple scab infection, respectively; and secondly, to determine if the concentration of synthetic fungicide and/or the number of spray applications can be reduced without an impact on efficacy if a synthetic fungicide is combined with a Ca or Si fertiliser. MATERIALS AND METHODS Container Trials Experiments used 4-year-old, cell-grown stock of Aesculus hippocastanum. Trees were 45 cm high, ± 4.5 cm. All trees were obtained from a commercial supplier (Blackmoor Estate, Blackmoor, Nr Liss, Hampshire, UK) during December to January as bare root stock and stored at 5 °C in a ventilated cold store 171 prior to potting up in February. Trees were potted into 10.0-L plastic pots filled with soil (loamy texture, 23% clay, 44% silt, 30% sand, 3% organic carbon, pH of 6.6) and supplemented with the controlled release, nitrogen-based (N:P:K 20:8:8) fertiliser ‘Enmag’ (Salisbury House, Weyside Park, Goldmar, Surrey, UK) at a rate of 5.0 g kg-1 soil. Following pot- ting, trees remained outdoors on a free-draining weed suppressant fabric at the University of Reading Shin- field Experimental Site, Reading, Berkshire, UK (51°43′N, −1°08′W). Trees were subject to natural climatic conditions and watered as required. The experiments were undertaken in 2016 and 2017. Throughout the experiments, 6 containerised trees per treatment were used. The experimental design adopted was a completely randomised block design. Field Experiment The apple trial site consisted of a 1.5-ha block of apple (Malus domestica cv. ‘Golden Delicious’) interspersed with individual trees of Malus domestica ‘Red Deli- cious’ and ‘Gala’ as pollinators. Planting distances were 3 m × 3 m spacing. The trees were planted in 2003 and trained under the central-leader system to an average height of 2.5 m ± 0.25 m, with mean trunk diameters of 12 cm ± 1.4 cm at 45 cm above the soil level. The trial site was located at the University of Reading Shinfield Experimental Site, University of Reading, Berkshire, UK (51°43′N, −1°08′W). The soil was a sandy loam containing 4% to 6% organic matter with a pH of 6.1, and available P, K, Mg, Na, and Ca were 55.3, 702.4, 188.2, 52.9, and 1,888 mg L-1 , respectively. Site management consisted of a 2-m- wide weed-free strip beneath the trees maintained with glyphosate (Roundup; Green-Tech, Sweethills Park, Nun Monkton, York, UK). No supplementary fertilisation was applied during the trials. A random- ised complete block was utilised in the experimental design. Six trees per treatment were used. A minimal insecticide (deltamethrin, product name Bandu, Headland Agrochemicals Ltd., Saffron Walden, Essex, UK) program was applied every 2 months during the growing season, commencing in May 2016 and 2017 (Nicholas et al. 2003), a standard practice followed at the University of Reading exper- imental site for orchard pest control. Treatments Penconazole, calcium, and silicon sprays were applied using a 5-L pump action sprayer, and trees were ©2021 International Society of Arboriculture
July 2021
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