Arboriculture & Urban Forestry 44(5): September 2018 randomized complete blocks plus a water control with a single tree as the experimental unit, giv- ing a total of 60 observations per response vari- able. Foliar sprays of each Si fertilizer, IR agent, and penconazole were applied until runoff us- ing a 10 liter knapsack sprayer (Cooper Pedlar, Agratech NW Ltd, Waterfoot, Rossendale, UK) at: • Topas (a.i. penconazole): 1.5 ml l-1 of water (Syngenta Crop Protection UK Ltd, Whittles- ford, Cambridge, UK). • Rigel (a.i. Polyether modified trisiloxane + Salicylaldehyde): 3 ml l-1 Future Technology Ltd, Henwood House, Henwood, Ashford, Kent, UK). ▶ Equivalent to 7 g Si per liter of water • Sirius (tetraethyl orthosilicate [Si (OC2 10 ml l-1 of water (Orion Future Technology Ltd, Henwood House, Henwood, Ashford, Kent, UK). ▶ Equivalent to 7 g Si per liter of water H5 )4 • Fossil (polyether modified trisiloxane): 10 ml l-1 of water (Orion Future Technology Ltd, Henwood House, Henwood, Ashford, Kent, UK). ▶ Equivalent to 7 g Si per liter of water • Salicylaldehyde (Sigma-Aldrich, Gillingham, Dorset, UK). • Sil-MATRIX (potassium silicate) 10 ml l-1 of water (Certis Granta Park, Riverside, Great Abington, Cambridge, UK). Tree Vitality Leaf chlorophyll measurements To keep the age of the leaves comparable through- out the experiment, measurements of chlorophyll content (SPAD) were made only on fully expanded mature leaves. In all cases measurements were tak- en from six leaves (two from the top of the crown, two in the center, and two at the base) per tree. A chlorophyll meter was used (SPAD-502 Chlo- rophyll Meter, Konica Minolta Sensing Europe B.V.). Chlorophyll was measured at the midpoint of the leaf next to the main leaf vein. Calibration was obtained by measurement of absorbance at 663 and 645 nm in a spectrophotometer (PU8800 Pye Unicam) aſter extraction with 80% v/v aque- ous acetone (regr. eq. = 5.75 + 0.055x; r2 adj = 0.96, P ≤ 0.001) (Lichtenthaler and Wellburn 1983). ]): of water (Orion 207 Scab severity Scab severity of leaves and fruit was assessed 28 September 2014 and 28 September 2015. Leaf scab severity of each tree was rated using a visual index- ing technique and ratings on the scale: 0 = No scab observed; 1 = less than 5% of leaves affected and no aesthetic impact; 2 = 5%–20% of leaves affected with some yellowing but little or no defoliation; 3 = 21%– 50% of leaves affected, significant defoliation and/ or leaf yellowing; 4 = 51%–80% of leaves affected, severe foliar discoloration; 5 = 81%–100% of leaves affected with 90%–100% defoliation. Scab severity on fruit was calculated on the scale: 0 = no visible lesions; 1 = <10% fruit surface infected; 2 = 10%– 25% fruit surface infected; 3 = 25%–50% fruit sur- face infected; 4 = >50% fruit surface infected. The individual ratings for each tree in each treatment were used as a measure of scab severity for statisti- cal analysis. Leaf scab severity ratings used in this study was based on UK and Ireland market stan- dards for fungicide evaluation of scab control (Butt et al. 1990; Swait and Butt 1990). Fruit scab sever- ity was based on a scale used by Ilhan et al. (2006). Fruit Yield Yield per tree was determined by weigh- ing all fruit on each tree at harvest and di- viding by the number of trees per treatment. was dissolved in HCl solution and transferred to a volumetric flask. Ammonium molybdate, tartaric acid, and ascorbic acid were added to this solu- tion, and the absorbance of the solution measured at 420 and 655 nm using a spectrophotometer CO3 and H3 BO3 (UV-1600; SHIMAZDU Co., Kyoto, Japan). The silica content was calculated per unit area and on a dry weight basis by comparing the absorbance with standard silicon solutions (10–1000 ppm). ©2018 International Society of Arboriculture Silicon Analysis Ten leaves and three fruits per tree were collected for tissue Si analysis. The leaves and fruit per tree were pooled for randomization purposes, washed with deionized water, and then placed in an oven for three days at 70°C. Dried leaves and fruit were then ground to pass through a 40-mesh screen. Leaf tissue Si concentration was determined following the method of Elliott and Snyder (1991). Leaves were ashed on platinum dishes and ash mixed with Na2 (5:1) to melt. Aliquot product
September 2018
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