206 (Datnoff and Nagata 1999). Si fertilizers also have been shown to reduce the incidence of powdery mildew in Kentucky bluegrass (Hamel and Heck- man 2000), improve disease resistance in zoysia grass to Rhizoctonia solani (Saigusa et al. 2000) and creeping bentgrass to Pythium aphanidermatum, Sclerotinia homoeocarpa and R. solani (Schmidt et al. 1999; Rondeau 200l; Uriarte et al. 2004). Induced resistance (IR) is the phenomenon whereby a plant’s own defense mechanisms are induced by treatment with a biological (i.e., weak- ened or attenuated fungal pathogen) or chemical agent (i.e., inorganic potassium and phosphate salts, low-molecular-weight proteins, unsaturated fatty acids; (Bécot 2000; Fobert and Després 2005; Percival et al. 2009). Developments in plant pro- tection technology have led to the formulation of a range of commercially available IR compounds such as harpin protein, potassium phosphite, and a range of salicylic acid analogs that are regis- tered for commercial use within the horticultural industry, although their availability differs between countries (Percival and Haynes 2008). Studies show that IR compounds can reduce disease sever- ity of fungal pathogens, such as Venturia inaequalis and V. pirina, with the level of pathogen suppres- sion, on occasion, comparable with synthetic fun- gicides (Christiansen et al. 1999; Bernards and Bastrup-Spohr 2008; Percival et al. 2009). The potential of Si fertilizers singly and in combina- tion with an inducing agent to manage scab dis- eases of trees has received little study. The majority of studies investigating the efficacy of IR agents on pathogen suppression were conducted under con- trolled laboratory and glasshouse conditions that do not reflect field environments (Agnostini et al. 2003; Percival et al. 2009). The purpose of this study was to investigate the association of Si fertil- izers singly and in combination with an IR agent as scab-protective compounds, using scab-sensitive species of apple (Malus cv. Golden Delicious) and pear (Pyrus communis ‘Williams’ Bon Chrétien’). MATERIALS AND METHODS Field Trials The apple trial site consisted of a 0.75 ha block of apple (Malus cv. Golden Delicious) interspersed with individual trees of Malus Red Delicious and ©2018 International Society of Arboriculture Percival: Evaluation of Silicon Fertilizers Gala as pollinators. The pear trial site consisted of a 0.90 ha block of Pyrus communis ‘Williams’ Bon Chrétien’ interspersed with individual trees of Pyrus communis Beth and Concorde. Plant- ing distances were 2 m × 2 m spacing. Trees were planted in 2003 and trained under a central-leader system to an average height 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 Shinfield Ex- perimental Site, Berkshire, UK (51°43N, -1°08W). The soil was a sandy loam containing 4%–6% organic matter; pH of 6.2; and available P, K, Mg, Na, and Ca were 52.0, 659.1, 175.2, 49.4, and 2,188 mg l-1 , respectively. Weeds were controlled using glyphosate (Roundup®; Green-Tech, Sweethills Park, Nun Monkton, York, UK). No watering or fertilization was applied during the two-year trial. Venturia inaequalis and V. pirina occur every year due to monocultures in the experimental area where the experiments were carried out. Prior to studies commencing in 2014 and 2015, trees were inspected in September 2013 and 2014, and only those trees with >50% of leaves affected with severe foliar discoloration and scab infection were used. A minimal insecticide program, based on deltame- thrin (Bandu, Headland Agrochemicals Ltd, Saffron Walden, Essex, UK), was applied every two months from May 2014 to September 2015. All sprays were applied using a Tom Wanner Spray Rig sprayer at 40 ml deltamethrin per 100 l-1 sprayed until runoff, 0.30 l-1 of water. Trees were insecticide per tree. Silicon and IR Treatments Treatments were applied at four distinct growth stages (Bevan and Knight 2001), namely: bud break (07 March 2014, 18 March 2015), green cluster (01 April 2014, 06 April 2015), 90% petal fall (08 May 2014, 21 May 2015), and early fruitlet (03 June 2014, 14 June 2015). Prior to each treat- ment, trees were inspected, and no symptoms of apple or pear scab were apparent. During spray treatments, polythene screens 2.5 m high were erected around each tree to prevent spray drift and cross contact with other trees. The base of the tree was covered with a 0.5 m × 0.5 m polythene mulch to prevent potential soil percolation. The treatments, 1 IR compound, 1 fungicide, 4 sili- con fertilizers × 4 spray times were applied in 10
September 2018
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
