Arboriculture & Urban Forestry 47(3): May 2021 drop can occur, reducing fruit quality and yield. Genetic resistance between pear species is limited, and no biocontrol options are currently available (Fitzner and Fischer 2005; Ivarsson 2011). Conse- quently, strategies for pear rust management are reli- ant upon repeated systemic fungicide sprays. Such an option is not available for pears growing within Euro- pean urban landscapes, as currently there are no syn- thetic fungicides registered or permitted for use (Percival 2018; BCPC 2020). Therefore, the develop- ment of an effective treatment to slow pear decline due to European pear rust and to protect valuable trees from infection is required. A potential alterna- tive to fungicides is the use of electrolysed oxidizing (EO) water (Buck et al. 2002; Al-Haq et al. 2003; Forghani 2019). EO water is generated by electroly- sis of a dilute solution of sodium chloride in an elec- trolysis chamber where anode and cathode electrodes are separated by a nonselective membrane made from nonwoven polyester fabric (Al-Haq et al. 2005). Water collected from the anode (EO water) has unique properties, such as high oxidation-reduction potential, low pH, presence of hypochlorous acid, and, importantly, has been shown to have strong bac- tericidal and fungicidal activity. EO water has been successfully used as a contact fungicide and for gen- eral sanitation in commercial glasshouses and is regarded as an environmentally benign alternative to fungicides (Al-Haq et al. 2002; Abbasi and Lazaro- vits 2006). Importantly, EO water presents negligible toxicity to humans, an important factor when apply- ing plant protection agents in densely populated urban areas. Due to its mode of action, i.e., physical rather than chemical, it is less likely to result in the development of pathogen resistance (Mueller et al. 2003; Al-Haq et al. 2005; Forghani 2019). Few, if any, studies exist evaluating EO water under field conditions and against a pathogen of urban landscape trees. Consequently, aims of this study were to investigate the efficacy of EO water for its potential plant protective properties against Euro- pean pear rust under field conditions. MATERIALS AND METHODS Field Site and Experimental Trees The pear trial site consisted of a 0.75 ha block of Pyrus cv. Conference. Planting distances were based on 2 m × 2 m spacing. The trees were planted in 2010 117 and trained under a central-leader system to an aver- age height of 2.0 m ± 0.20 m, with mean trunk diam- eters of 4.0 cm ± 0.8 cm at 45 cm above the soil level. The trial site was located at Aston Manor Orchard, Tiverton, Devon, UK (50°53′37″N, 3°29′53″W). Fifteen soil cores from the 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 and available P, K, Mg, Na, and Ca of 51.3 mg/L, 680.9 mg/L, 199.6 mg/L, 48.3 mg/L, and 2,329 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. Due to a monoculture planting site, the pear trees suffered from pear rust infection on an annual basis. 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 10-L knapsack sprayer at 70 mL deltamethrin (Bandu; Barrettine Group, St. Ivel Way, Warmley, Bristol, UK) per 100 L of water. Trees were sprayed until runoff, generally 0.40 L of insecticide per tree. EO Water and Fungicide Treatments EO water and fungicide (boscalid + pyraclostrobin, 0.9 g/L of water [trade name Signum; Barrettine Group, St. Ivel Way, Warmley, Bristol, UK]) treat- ments were applied 4 times over 2 growing seasons, namely, April 28, May 09, May 28, and June 10 in 2017, and April 26, May 11, May 28, and June 12 in 2018 (Ivarsson 2011). Two guard trees were located between each treated tree to prevent dispersal of sprays and possible cross contact with other trees. Ten trees per treatment were used in a completely randomised block design. Foliar sprays of EO water and boscalid + pyraclostrobin were applied until run- off using a 10-L knapsack sprayer (Cooper Pegler; Agratech NW Ltd., Waterfoot, Rossendale, UK), generally 0.40 L of product per tree. Plant Vitality Assessments Measurements were made towards the cessation of the growing season (24–26 September 2017; 25–27 ©2021 International Society of Arboriculture
May 2021
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