170 Percival and Graham: Calcium and Silicon Fertiliser and Fungicide for Pathogen Management Arboriculture & Urban Forestry 2021. 47(4):170–181 https://doi.org/10.48044/jauf.2021.016 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & Calcium and Silicon Fertiliser Influence on Fungicide Efficacy Against Leaf Blotch and Apple Scab Management By Glynn C. Percival and Sean Graham Abstract. Management of fungal diseases within urban landscapes relies heavily on repeat fungicide sprays. Environmental concerns have led to a need to eliminate or reduce fungicide use. Foliar sprays of calcium- (Ca) and silicon- (Si) based fertilisers have been shown to reduce symp- tom severity of several fungal pathogens. The aim of our research was to evaluate the influence of Ca chloride, Ca metasolate, tetra ethyl silicate, and potassium silicate fertilisers, applied independently and in combination with a synthetic fungicide (penconazole) at full and half strength, on apple scab (Venturia inaequalis) and Guignardia leaf blotch (Guignardia aesculi) symptom severity, as well as leaf chlorophyll content, fruit yield, and crown volume. Trials used container-grown Aesculus hippocastanum and field-grown Malus domestica cv. ‘Golden Delicious’. Applications of Ca, Si, and penconazole sprays alone significantly reduced scab and leaf blotch severity compared to water-sprayed controls; however, a significant difference between the type of Ca and Si fertilisers was recorded. A combined mix of a Ca or Si fertiliser with a full or half dose of penconazole was more effective at reducing symptom severity of both foliar pathogens than a full or half dose of pen- conazole alone. Data analysed with Limpel’s formula indicated positive synergistic effects between Ca and Si and penconazole in some, but not all, cases. The integration of Ca and Si foliar sprays as an alternative to, or additive with, penconazole for scab and leaf blotch management appears feasible based on results of our studies and may have applicability against other fungal pathogens. Keywords. Disease Management; Fruit; Holistic Approach; Integrated Pathogen Management; Pathogen Control; Plant Health Care; Urban Landscapes. INTRODUCTION Foliar pathogens such as apple scab (Venturia inaequa- lis) and Guignardia leaf blotch (Guignardia aesculi, horse chestnut leaf blotch) represent a worldwide problem for ornamental trees planted into UK, US, and European landscapes (Hersh et al. 2012; Hantsch et al. 2013, 2014; Percival 2018). Heavy disease inci- dence can result in premature leaf drop, increased rate of crown dieback, and a reduction in carbon alloca- tion to fine roots, trunk, and twigs (Villalta et al. 2004; Hantsch et al. 2013; Oliva et al. 2014). Repeat annual defoliations and subsequent loss of photosynthetic productivity can result in tree decline and sometimes death, resulting in expensive tree replacement costs (Tello et al. 2005; Oliva et al. 2014; Stravinskienė et al. 2015; Percival 2018). In addition, premature defo- liation makes a tree aesthetically undesirable, and many of the functional benefits urban trees provide ©2021 International Society of Arboriculture (absorbing pollutants and dust, UV protection through shading, evaporative cooling) are significantly reduced (Morgenroth et al. 2016; Vogt et al. 2017). To prevent foliage loss and reduction of functional qualities, repeat fungicide sprays are usually undertaken (Carisse and Dewdney 2002; Berrie and Xu 2003; Hailey and Percival 2014). However, new approaches to scab management are needed, as strains of V. inaequalis have developed resistance to synthetic fungicides. Similarly, public concern has increased over fungi- cide residues, and arborists manage trees in densely populated areas where potential fungicide contact with pedestrians could lead to litigation claims (Chris- tiansen et al. 1999; Carisse and Dewdney 2002; Pato- cchi et al. 2004). Calcium (Ca) is a major macronutrient in trees, important to the structural integrity of cell walls and plasma membranes (Khalifa et al. 2009; Fromm Guignar dia
July 2021
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