©2023 International Society of Arboriculture Arboriculture & Urban Forestry 49(2): March 2023 67 2 = 5% to 20% of leaves affected with some yellowing but little or no defoliation 3 = 21% to 50% of leaves affected, significant defoliation and/or leaf yellowing 4 = 51% to 80% of leaves affected, severe foliar discolouration 5 = 81% to 100% of leaves affected with 90% to 100% defoliation Scab severity on fruit (field trial only) was calcu- lated using the scale: 0 = No visible lesions 1 = < 10% fruit surface infected 2 = 10% to 25% fruit surface infected 3 = 26% to 50% fruit surface infected 4 = > 50% fruit surface infected The individual ratings for each tree in each treat- ment were used as a measure of scab severity for sta- tistical analysis. Leaf scab severity ratings used in this study were based on UK and Ireland market stan- dards for fungicide evaluation of scab control (Butt et al. 1990; Swait and Butt 1990). Fruit scab severity was based on a scale used by Ilhan et al. (2006). Fruit Yield: Field Trial Only Fruit was not thinned during July and August 2019; all were allowed to reach maturity. Fruit yield per tree was determined by weighing all of the fruit (symp- tomatic and asymptomatic) on each tree at harvest and dividing by the number of fruits per tree. Statistical Analysis All data were analysed using Analysis of Variance (ANOVA), and where appropriate, differences between means were determined using Tukey’s Honest Signif- icant Difference test (P = 0.05) using Genstat 19th edition (VSNi International, Hemel Hempstead, England, UK). RESULTS Container Trials Damaging outbreaks of apple scab were recorded on control trees as indicated by an average leaf scab symptom severity rating of 3.8 on M. sylvestris at the cessation of the 2018 growing season (Table 2). None of the treated or control trees died as a result of scab attack during the course of the study. However, chitin Table 1. Products, active ingredient, concentration, directions for use, and supplier of treatmentsa used. Commercial name Active ingredient Concentration applied Directions for use Supplier Topas Penconazole 1.5 mL/L of water See “Materials and Methods” Syngenta UK Ltd, Fulbourn, Cam- bridgeshire, UK Chitin Chitin 120 g/m2 under the canopy = 360 g per tree applied Once as a top dressing in March or as buds swell Tidal Vision, Bellingham, WA, USA Chitosan Chitosan 120 g/m2 under the canopy = 360 g per tree applied Once as a top dressing in March or as buds swell Tidal Vision, Bellingham, WA, USA Crab meal Crab meal 0.75 kg under the canopy per tree applied Once as a top dressing in March or as buds swell Ocean Crest Seafoods Inc., Gloucester, MA, USA Liquid chitosan Chitosan 1.0 mL/5 L of water per m2 under the canopy = 3 mL per tree applied One weekly drench for the first three weeks, and then one drench per month throughout the growing season; start first drench in March or as buds swell Viresco UK Ltd, Thirsk, North Yorkshire, UK Agrinos 5-0-0 Chitin 0.8 g/L of water per m2 under the canopy = 2.4 g per tree applied Every 2 weeks throughout the growing season; start first drench in March or as buds swell Hortifeeds, Park Farm, Kettlethorpe, Lincoln, UK Control Water – – – aAll treatments based on manufacturers’ recommended efficacy rates.
March 2023
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