Arboriculture & Urban Forestry 47(4): July 2021 chloride, singly and in combination, significantly reduced leaf and fruit scab severity symptoms (Tables 2 and 5) and significantly increased fruit yield, leaf chlorophyll content, and crown volume compared to water-treated controls (Tables 3, 4, and 5). Greater effi- cacy (reduced leaf and fruit scab severity, increased leaf chlorophyll content, fruit yield, and crown vol- ume) was recorded using combinations of penconazole at full strength + tetra ethyl silicate or penconazole at full strength + Ca chloride compared to each product applied singly (Tables 2, 3, 4, and 5). Similarly, 3 spray applications of penconazole at half strength (0.5 mL L-1 DISCUSSION ) + tetra ethyl silicate or penconazole at half strength + Ca chloride had greater efficacy as scab protectant compounds compared to spray appli- cations of penconazole at half strength alone (Tables 2, 3, 4, and 5). These effects were primarily additive, with two exceptions: penconazole at half strength + Ca chloride on leaf scab severity symptoms (Table 2) and crown volume (Table 4), where a synergistic effect based on Limpel’s formula was recorded. There is a significant body of literature that describes Si and Ca nutrition reducing the intensity and severity of fungal and bacterial pathogen symptomology. Examples include rice blast (Magnaporthe grisea, anamorph = Pyricularia grisea), grey leaf spot, pow- dery mildew, Rhizoctonia solani, Pythium aphanid- ermatum, Sclerotinia homoeocarpa, Phoma exigua var. foveata, brown rot of fruit trees (Monilinia fructi- cola), apple scab (V. inaequalis), pear scab (V. pirina), and fireblight (Erwinia carotovora subsp. atrosep- tica)(Uriarte et al. 2004; Ippolito et al. 2005; Elmer et al. 2006; Springer et al. 2007; Khalifa et al. 2009; Wang et al. 2017; Percival 2018). In support of this, results of this study show that applications of Si- and Ca-based fertilisers alone reduced leaf blotch and apple scab severity of containerised and field-grown trees, respectively, when applied 3 times during a growing season. Supplementing plants with Si and/or Ca has been shown to act primarily in two ways. The first is by physical alterations to leaf structure caused 175 Table 3. The influence of calcium and silicon fertilisers and synthetic fungicide combinations applied as foliar sprays on leaf chlorophyll content (SPAD) of Aesculus hippocastanum (container-grown stock) with Guignardia leaf blotch (Guignardia aesculi) and Malus domestica cv. 'Golden Delicious' (field trials) with apple scab (Venturia inaequalis). A. hippocastanum SPAD Treatment Water (control) Penconazole (1 mL × 6 sprays) Penconazole (1 mL) Penconazole (0.5 mL) Tetra ethyl silicate (10 mL) Penconazole (1 mL) + tetra ethyl silicate (10 mL) Penconazole (0.5 mL) + tetra ethyl silicate (10 mL) Potassium silicate (10 mL) Penconazole (1 mL) + potassium silicate (10 mL) Penconazole (0.5 mL) + potassium silicate (10 mL) Ca chloride (2.5 g) Penconazole (1 mL) + Ca chloride (2.5 g) Penconazole (0.5 mL) + Ca chloride (2.5 g) Ca metasolate (2.5 g) Penconazole (1 mL) + Ca metasolate (2.5 g) Penconazole (0.5 mL) + Ca metasolate (2.5 g) Treatment = synergistic effect according to Limpel’s formula. Add product alone. 2016 36.5a 47.0g 40.5abcdef 37.5ab 39.0abcd 43.0defg (Add 40.0abcdef (Add 38.8abc ) ) 43.3efg (Add ) 39.2abcde (Add 41.4bcdef 43.5fg (Add 42.8cdef(Add 38.9abc ) ) 42.2cdef (Add 39.1abcde (Add < 0.001 ) ) ) 2017 34.6a 46.9h 39.8cde 35.9ab 39.4bcde 44.1fgh (Add 41.5ef (Add 36.8abc ) ) 44.0fgh (Add 41.1defg (Add 39.8cde 44.7gh (Add 47.0h (Syn 37.4abcd ) 41.5efg (Add 40.1cdef (Add < 0.001 Lower case letters indicate significant differences between means for each evaluation date by LSD (P = 0.05). Syn All values mean of 6 trees, 10 leaves per tree. ©2021 International Society of Arboriculture ) ) ) ) ) M. domestica cv. 'Golden Delicious' SPAD 2016 28.8a 38.6g 32.1bcd 30.5ab 31.6abc 33.4bcd (Add 34.1cdef (Add 31.3ab 33.8cde (Add 32.4bcd (Add 35.1def 36.9efg (Add 37.1fg(Add 30.9abc ) 33.1bcd (Add 32.7bcd(Add < 0.001 ) ) ) ) ) ) ) 2017 27.1a 36.9de 32.8bc 31.5b 32.0bc 34.6bcd (Add 32.9bc (Add 32.5bc ) ) 35.0bcde (Add 32.1bc (Add 33.9bcd ) 35.1cde (Add 38.2e (Add 32.8bc ) 34.6bcd (Add 33.5bcd (Add < 0.001 = additive effect if values did not exceed Limpel’s formula but were greater than the effect of each ) ) ) )
July 2021
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