360 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 sites were located at the University of Reading Shin- field Experimental Site, University of Reading, Berk- shire (51°43’ N, -1°08’ W). Fifteen soil cores from each apple and pear trial site were taken to a depth of 20 cm and radius of 5 cm based on an 8.0-m “W” pattern as stipulated under UK soil sampling procedures (Tytherleigh 2008). The soil was a sandy loam containing 5.2% organic matter with a pH of 6.6; available P, K, Mg, Na, and Ca were 54.3, 685.2, 195.3, 45.1, and 2300 mg/L, respectively. Weeds were controlled chemically using glyphosate (Roundup, Green-Tech, Sweethills Park, Nun Monkton, York, UK) throughout experiments. No watering or fertilisation was applied during the trial. Historically, trees suffered from apple and pear scab infection on an annual basis. Prior to the trial commenc- ing in 2017, trees were inspected in September 2016, and only those apple and pear trees with > 50% of leaves affected with severe foliar discolouration and subsequent scab infection were included in the trial. A minimal insecticide program based on the residual pyrethroid insecticide deltamethrin (product name Bandu, Headland Agrochemicals Ltd, Saffron Walden, Essex, UK) was applied every 2 months commencing in May 2017 to September 2017. All sprays were applied using a Tom Wanner Spray Rig sprayer at 40 mL del- tamethrin (Bandu) per 100 L of water. Trees were sprayed until run-off, generally 0.30 L insecticide per tree. IR and Fungicide Treatments IR and fungicide treatments were applied either (i) preventatively (no visible symptoms of apple or pear Percival: Induced Resistance and Scab Severity scab at the time of treatment) at four growth stages identified as key application times for scab control under field conditions (Bevan and Knight 2001), namely: bud break (March 9), green cluster (April 8), 90% petal fall (May 16), early fruitlet (June 9); or (ii) curatively, i.e., 5% to 20% of leaves infected with some yellowing, but little or no defoliation at the time of treatment on June 19, July 10, July 31, and August 18. Preventative and curative penconazole (synthetic fungicide) sprays occurred on the same dates as IR drench applications. During spray treatments, poly- thene screens 2.5 m high were erected around each tree to prevent dispersal of sprays and possible cross contact with other trees. The base of the tree was cov- ered with a 0.5 m × 0.5 m polythene mulch to prevent potential soil percolation. The treatments, 4 IR agents, 1 fungicide, and 1 water control × 2 treatments (pre- ventative vs. therapeutic), were applied in 6 randomised complete blocks, plus a water control with a single tree as the experimental unit (Table 1). Foliar sprays of penconazole were applied until run-off using a hand sprayer. As a root drench, 5 L of each IR agent were applied to the soil surface by pouring into a 50- to 60-mm-wide, 20- to 30-mm-deep trench at the base of each tree. Five litres was selected as this was the mean area under the canopy to represent 1 L/m2 of soil surface area. Plant Vitality Assessments Measurements were made towards the cessation of the growing season (24 September 2017). To keep the physiological age of the leaves comparable through- out the experiment, plant vitality measurements were made only on fully expanded, mature green leaf tissue. Table 1. Products, active ingredient, concentration, acronym, and supplier of treatments used. Commercial name Topas Active ingredient Penconazole Messenger Phusion Rigel-G Liquid Chitosan Control Harpin protein Potassium phosphite Concentration applied 1.5 mL/L of water 0.005 g/L of water 10.0 mL/L of water Salicylic acid derivative 3.0 mL/L of water Chitosan Water 1.0 mL/L of water - All treatments based on manufacturers’ recommended efficacy rates. ©2020 International Society of Arboriculture Acronym - HP PP SA LC - Supplier Syngenta Crop Protection UK Ltd, Whittlesford, Cambridge, UK EDEN Bioscience Corporation, N. Bothell, Washington, USA Orion Future Technology Ltd, Henwood House, Henwood, Ashford, Kent, UK Orion Future Technology Ltd, Henwood House, Henwood, Ashford, Kent, UK Viresco (UK) Ltd, Thirsk, North Yorkshire, UK -
September 2020
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