Arboriculture & Urban Forestry 36(3): March 2010 2007). Research in Australia and the U.S. has found potassium phosphite salts to be extremely effective in the control of patho- gens belonging to the Oomycetes group, such as Phytophthora spp., Pythium spp., and the Downy Mildew diseases (Jackson et al. 2000; Miller et al. 2006). In addition, potassium phosphite has been shown to suppress fungal pathogens that fall outside this group such as Venturia inaequalis (apple scab) (MacHardy and Jeger 1983), and bacterial diseases such as Erwinia amylovora (apple fire blight). The objective of this study was to investigate the use of potassium phosphite (Pi) alone and in combination with a reduced dose of synthetic fungicide (myclobutanil) to control pear scab under field conditions. Within the UK, my- clobutanil, a systemic, protectant, and curative triazole fungi- cide, is commercially registered for the control of pear scab. MATERIALS AND METHODS Field Trials The pear trial site consisted of a 0.90 ha block of Pyrus com- munis ‘Williams’ Bon Chrétien’ interspersed with individual trees of Pyrus communis Beth and Concorde. Pyrus communis ‘Williams’ Bon Chrétien’ was chosen for experimental purposes due to its sensitivity to pear scab infection. Planting distances were based on 2 m × 2 m spacing. The trees were planted in 2003 and trained under the central-leader system to an aver- age height of 2.5 m ± 0.25 m, and with mean trunk diameters of 12 cm ± 1.4 cm at 45 cm above the soil level. The trial site was located at the University of Reading Shinfield Experimental Site, University of Reading, Berkshire, UK (51°43N, -1°08W). The soil was a sandy loam containing 3%–5% organic matter, pH of 6.1. Weeds were controlled chemically using glyphosate (Roundup; Green-Tech, Sweethills Park, Nun Monkton, York, UK), throughout experiments. No water, fertilizer, or plant growth regulators were applied during the two-year trial. His- torically, the pears suffered from pear scab infection on an an- nual basis. Consequently, prior to the trial commencing in 2006 and 2007, trees were inspected in September 2005 and 2006 and only those trees with > 50% of leaves affected with pear scab infection were used in the trials. A minimal insecticide pro- gram based on the residual pyrethroid insecticide deltamethrin (product name Bandu, Headland Agrochemicals, Ltd., Saffron Walden, Essex, UK) was applied every three months during each growing season commencing in May 2006 to September 2007. All sprays were applied using a Tom Wanner Spray Rig sprayer at 40 ml deltamethrin (Bandu) per 100 liters of water. Trees were sprayed until runoff, generally 0.35 liter insecticide per tree. Spray Treatments Potassium phosphite (Pi; 300 g phosphorous acid per liter water), trade name Phoenix (Orion Future Technology, Ltd., Henwood House, Henwood, Ashford, Kent, UK) and myclobutanil, trade name Systhane 20EW (Landseer, Ltd., Chelmsford, Essex, UK) sprays were applied at four growth stages identified as key treat- ment times for scab control under field conditions (Bevan and Knight 2001), namely: bud break (March 11, 2006; March 17, 2007), green cluster (April 1, 2006; April 7, 2007), 90% petal fall (May 13, 2006; May 19, 2007), and early fruitlet (June 1, 2006; 87 June 8, 2007). Prior to spray treatments, trees were inspected and no visible symptoms of pear scab were apparent. During spray treatments polythene 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 covered with a 0.5 m × 0.5 m polythene mulch to prevent potential soil percolation. The experimental treatments and the applica- tion protocol for the treatments were as follows: 1) water-treated control 2) Pi at 10 ml per liter water 3) Pi at 20 ml per liter water 4) Myclobutanil at 0.3 ml per liter water (manufacturer’s rec- ommended strength) 5) Myclobutanil at 0.075 ml per liter water (25% of manufac- turer’s recommended strength). 6) Pi at 10ml + myclobutanil at 0.075ml per liter water. 7) Pi at 20ml + myclobutanil at 0.075ml per liter water. The treatments (one water control; two Pi; two my- clobutanil; two Pi + myclobutanil combinations), were ap- plied in 10 randomized complete blocks with a single tree as the experimental unit, giving a total of 70 observa- tions per response variable. Foliar sprays of each prod- uct were applied until runoff using a hand sprayer (Coo- per Pegler, Watling Street, Clfton upon Dunsmore, UK). Scab Incidence and Severity The degree of protection conferred by each treat- ment was assessed by recording scab incidence and se- verity at monthly intervals from July to September. Scab incidence: At each assessment, 100 leaves and were 30 fruits of a chosen arbitrarily from different sides tree. A leaf or a fruit was considered to be in- fected if at least one visible scab lesion was present. Scab severity of leaves and fruit was assessed visu- ally. Leaf scab severity of each tree was rated using a visual indexing technique and ratings on the scale: 0 = No scab observed; 1 = less than 5% of leaves affected and no aes- thetic impact; 2 = 5%–20% of leaves affected with some yel- lowing 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 following scale: 0 = no visible lesions; 1 = <10% fruit surface in- fected; 2 = 10%–25% fruit surface infected; 3 = 25%–50% fruit surface infected; 4 = >50% fruit surface infected. Leaf scab severity ratings used in this study was based on UK and Ireland market standards for fungicide evaluation of scab control (Butt et al. 1990; Swait and Butt 1990). Fruit scab severity was based a scale used by Ilhan et al. (2006). Scab severity ratings were undertaken by three in- dependent BASIS (British Agrochemical Standards In- spection Scheme) qualified crop protection specialists. ©2010 International Society of Arboriculture
March 2010
| Title Name |
Pages |
Delete |
Url |
| Empty |
Ai generated response may be inaccurate.
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.
Downloading PDF
Generating your PDF, please wait...
This process might take longer please wait
