Arboriculture & Urban Forestry 44(5): September 2018 Arboriculture & Urban Forestry 2018. 44(4):205–214 205 Evaluation of Silicon Fertilizers and a Resis- tance Inducing Agent for Control of Apple and Pear Scab under Field Conditions Glynn C. Percival Abstract. Two field trials were conducted using established apple (Malus cv. Golden Delicious) and pear (Pyrus communis ‘Wil- liams’ Bon Chrétien’) to assess the efficacy of a range of silicon (Si) fertilizers, a resistance-inducing (IR) agent based on salicylic acid and a combination of Si + IR when applied at four growth stages of tree development (i.e., bud break, green cluster, 90% petal fall, early fruitlet) against the foliar pathogens apple (Venturia inaequalis) and pear (V. pirina) scab. In addition, a comparative eval- uation of a conventional synthetic fungicide (penconazole) used within the UK for apple and pear scab control was performed. Greatest protection against apple and pear scab was provided by a combination of a Si fertilizer + IR agent and the synthetic fungi- cide penconazole in both the 2014 and 2015 field trials where statistically comparable degrees of control were achieved. Efficacy as scab-protectant compounds (i.e., reduced scab severity of leaves and fruit) enhanced leaf chlorophyll content and fruit yield, and was confirmed when each Si fertilizer was applied at four growth stages during two growing seasons; however, there was little difference in the degree of control conferred by each Si fertilizer. The IR agent used alone proved the least effective scab protectant compound. Key Words. Apple Scab; Fungicide; Integrated Disease Management; Orchard Management; Pathogen Control; Pear Scab; Plant Health Care; Urban Landscapes. Apple and pear scab caused by the fungal patho- gens Venturia inaequalis and V. pirina respectively can be devastating to apples (Malus spp.) and pears (Pyrus spp.), reducing fruit quality, market- able yield, and aesthetics (Cuthbertson and Mur- chie 2003; Jamar et al. 2010; Hailey and Percival 2014). The scab fungi infect leaves, petioles, and fruit, with initial symptoms appearing as olive- green spots on the leaf or leaf petiole. As infec- tion develops, leaves turn yellow and drop pre- maturely, while infected fruit becomes deformed, scabby, and can drop before maturity (Jamar et al. 2010). Within Europe, suppliers, vendors, and growers of apples and pears adopt a zero-tolerance policy toward scab. As a result, the economics of fruit production require frequent application of synthetic fungicides throughout the growing season. Increased pathogen insensitivity to syn- thetic fungicides, coupled with public demands to reduce use, stimulated by greater awareness of environmental and health issues, has placed em- phasis on the development of alternative control strategies (Gozzo 2003; Villalta et al. 2004; Per- cival and Haynes 2008; Hailey and Percival 2014). The potential benefits of silicon (Si) nutri- tion in plants include enhancement of growth and yield; improvement of mechanical properties (soil penetration by roots, resistance to lodging); reduced transpiration; and resistance to drought, salt, and heavy metal toxicities (Fauteux et al. 2005). In addition, Si-based soil fertilizers and sprays have proved effective in controlling soil- borne and foliar fungal pathogens of several plant species (Ma 2004). In rice, for example, Si has been demonstrated to control rice blast, (Magna- porthe grisea, anamorph = Pyricularia grisea), as effectively as commercially available fungicides as well as reduce the number of fungicide appli- cations (Datnoff et al. 2001; Seebold et al. 2004). Studies of the influence of Si fertilizers on gray leaf spot development in St Augustine grass under greenhouse conditions demonstrated that Si sig- nificantly reduced disease progress by 44% to 78% and whole-plant infection by 2.5% to 50.5%. ©2018 International Society of Arboriculture
September 2018
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