co
fi
cien
Accepted 12 August 2008
Keywords:
Urban trees
Disease control
Foliar pathogens
Integrated disease management
awareness of environmental and health issues, as well as devel-
opment of strains of V. inaequalis (Cooke) G. Wint. resistant to
synthetic fungicides limit the effectiveness of conventional pesti-
cide management strategies (Akbudak et al., 2006; Hagan and
Akridge, 2007). Likewise increased government legislative restric-
tions regarding the use and application of pesticides further
cereals, vegetables, fruit and ornamentals, including rusts (Puccinia,
Uromyces spp.), grey mould (Botrytis cinerea Pers.), eyespot
(Septoria nodorum Berk.) and leaf spot (Pyrenophora spp.) (Blaedow
et al., 2006; Sutherland andWalters, 2001; Sutherland and Walters,
2002). Film forming polymers act as a physical protective barrier
against invading foliar pathogens at the leaf surface and prevent
adherence of spores that subsequently inhibited germ tube devel-
opment (Han, 1990; Osswald et al., 1984). As film forming polymers
act by physical and not chemical means, they are not subject to the
Contents lists availab
o
.e l
Crop Protection 28 (2009) 30–35* Corresponding author. Tel.: þ44 780 891 5865.1. Introduction
Apple scab caused by Venturia inaequalis (Cooke) G. Wint. is the
most economically devastating pathogen of ornamental and fruit-
ing apples world wide (Blaedow et al., 2006). As producers,
suppliers and vendors of apples generally adopt a zero tolerance
policy towards scab on fruit, conventional orchard and production
systems rely heavily on repeated fungicide sprays throughout the
growing season (Berrie and Xu, 2003; Percival and Boyle, 2005).
Public demands to reduce pesticide use, stimulated by greater
emphasize the need to develop alternative pathogen management
systems (Marco et al., 1994; Walters, 2006).
Film forming polymers are widely used as spray adjuvants
within the agricultural, forestry and horticultural industries
(Backman, 1978). Their main functions are to reduce weathering
and extend pesticide efficacy, act as stickers/spreaders to improve
distribution and adherence of agrochemicals, and decrease water
loss and wilting of young transplants (Gale and Hagan, 1996).
Studies using film forming polymers as an alternative to fungicides
have found several to be effective in controlling foliar pathogens ofFungicides
Pathogen control
Orchard management
Tree productionE-mail address: gpercival@bartlettuk.com (G.C. Pe
0261-2194/$ – see front matter  2008 Elsevier Ltd.
doi:10.1016/j.cropro.2008.08.005laboratory in vitro conditions, supported by two field trials using established apple cv. Golden Delicious
to further assess the efficacy of foliar applied film forming polymers as scab protectant compounds. All
film forming polymers used in this investigation (Bond, Designer, Nu-Film P, Spray Gard, Moisturin,
Companion PCT12) inhibited germination of conidia, subsequent formation of appressoria and reduced
leaf scab severity using a detached leaf bioassay. Regardless of treatment, there were no obvious trends in
the percentage of conidia with one to four appressoria 5 days after inoculation. The synthetic fungicide
penconazole resulted in the greatest levels of germination inhibition, appressorium development and
least leaf scab severity. Under field conditions, scab severity on leaves and fruit of apple cv. Golden
Delicious treated with a film forming polymer (Bond, Spray Gard, Moisturin) was less than on untreated
controls. However, greatest protection in both field trials was provided by the synthetic fungicide pen-
conazole. Higher chlorophyll fluorescence Fv/Fm emissions in polymer and penconazole treated trees
indicated less damage to the leaf photosynthetic system as a result of fungal invasion. In addition, higher
SPAD values as measures of leaf chlorophyll content were recorded in polymer and penconazole treated
trees. Application of a film forming polymer or penconazole resulted in a higher apple yield per tree at
harvest in both the 2005 and 2006 field trials compared to untreated controls. Results suggest appli-
cation of an appropriate film forming polymer may provide a useful addition to existing methods of
apple scab management.
 2008 Elsevier Ltd. All rights reserved.Article history:
Received 16 May 2008
Received in revised form 11 August 2008A detached leaf bioassay was used to determine the influence of several film forming polymers and
a conventional triazole fungicide on apple scab (Venturia inaequalis (Cooke) G. Wint.) development underEvaluation of film forming polymers to
(Cooke) G. Wint.) under laboratory and
Glynn C. Percival*, Shirley Boyle
R.A. Bartlett Tree Research Laboratory, Plant Science Laboratories, School of Biological S
a r t i c l e i n f o a b s t r a c t
Crop Pr
journal homepage: wwwrcival).
All rights reserved.ntrol apple scab (Venturia inaequalis
eld conditions
ces, Whiteknights, The University of Reading, Reading RG6 6AS, UK
le at ScienceDirect
tection
sevier .com/locate/croprostringent government legislative restrictions that relate to the use

and application of conventional pesticides (Anon., 2008). Current
film forming polymers are also less phytotoxic than synthetic
fungicides to leaf tissue, permeable to atmospheric gases and allow
penetration of solar radiation so consequently have little detri-
mental effects on tree biology when applied at high concentrations
(Fuller et al., 2003). Consequently, film forming polymers poten-
tially offer a cheaper (polymers cost 40–80% less than conventional
fungicides) and environmentally more acceptable system
compared with current fungicide spray methodology for reducing
scab related yield losses. The efficacy of film forming polymers
against the fungal pathogen apple scab (V. inaequalis (Cooke)
paper. Five plates with 12 detached leaves per plate (60 leaves per
treatment) were inoculated by spraying with an axenic conidial
light/8 h dark photoperiod from white fluorescent tubes at
40 mmolm2 s1 light intensity (Yepes and Aldwinckle, 1993a).
At day 5 post inoculation the percentage of conidia that had
germinated, the percentage that had formed appressoria and the
number of appressoria per conidium were determined on 100
spores from 20 leaves, 5 spores per leaf (Yepes and Aldwinckle,
1993b). Leaves were decolorized overnight by immersing in 99%
cold methanol and stained with periodic acid–basic fuchsin. Whole
leaves were mounted on glass slides in glycerol and examined by
light microscopy. The remaining 40 leaves per treatment were
assessed at day 35 after inoculation using the leaf scab severity
ke) G
ett
ette
prea
r/sti
nspi
G.C. Percival, S. Boyle / Crop Protection 28 (2009) 30–35 31suspension (106 conidia/ml) that included an mixture of races 1–5
of V. inaequalis. The fungus was grown in wick cultures on 4% malt
extract, and spores were collected, centrifuged (2000g, 5 min), and
re-suspended in distilled water. After inoculation, all plates were
sealed with a thin polythene film (Parafilm) permeable to air but
not water and incubated in a growth chamber at 191 C, 16 h
Table 1
Selected film forming polymers evaluated for the control of Venturia inaequalis (Coo
Product Active ingredient Property
Water (control) – –
Bond Alkyl phenyl hydroxyl polyoxyethylene Sticker/w
Designer Styrene–butadiene copolymerþ polyalkylene
oxide modified heptamethyl trisiloxane
Super w
Nu-Film P Poly-1-p menthene Sticker/s
Spray Gard Di-1-p menthene Extende
Moisturin Ammonium hydroxideþ naphthaleneþ
1,2,4 trimethylbenzene
Anti-traG. Wint.) has received little attention. Due to this lack of informa-
tion a detached leaf bioassay was used to determine the influence
of several film forming polymers on apple scab development under
laboratory in vitro conditions, supported by two field trials using
established apple cv. Golden Delicious trees to further assess the
efficacy of foliar applied polymers as scab protectant compounds.
2. Materials and methods
2.1. Laboratory in vitro experiments
Sixty fully expanded leaves were excised from actively growing
shoots of field grown apple cv. Golden Delicious 28 days after leaf
flush (mid-May), a time when leaf material shows maximum
photosynthetic performance (Kitao et al., 1998) with no visible
symptoms of scab development. All leaf material was prepared
within 2 h of collection. Inoculation experiments were done under
sterile conditions using a laminar flow transfer hood. Leaves were
surface sterilized by immersing in sodium hypochlorite for 30 s and
then rinsed in sterile distilled water for 1 min prior to drying on
Whatman filter paper (Muhammed et al., 1996). Immediately
following drying, leaves were immersed in a 10 ml l1 (1% solution)
film forming polymer solution (Table 1) and allowed to dry for 1 h
at ambient temperature. In addition, a comparative evaluation of
the fungicide Topas (a.i. penconazole 10% emulsfiable concentrate)
a protectant triazole fungicide with antisporulant activity (Syn-
genta Crop Protection UK Ltd, Whittlesford, Cambridge, UK)
commercially used for apple scab control was conducted by
immersing leaves at the manufacturers recommended rate of
1.5 ml l1 of water. Twenty non-polymer leaves acted as controls.
Leaves were then placed abaxial surface down in plastic Petri-
dishes lined with moist (sterile distilled water) Whatman filterCompanion
PCT12
25% Polyacrylamide Spreader/stirating for field trial evaluations. In vitro laboratory experiments
occurred in 2005 and were repeated in 2006.
2.2. Field trials
The apple trial site consisted of a 0.75 ha block of apple cv.
Golden Delicious interspersed with individual trees of Golden
Crown, Red Delicious and Gala as pollinators. Golden Delicious was
chosen for experimental purposes due to its sensitivity to apple
scab infection. Planting distances were based on 2 2 m spacing.
The trees were planted in 2003 and trained under the central-
leader system to an average height of 1.5 0.15 mwith mean trunk
diameters of 101.2 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 (51430N, 1080W).
The soil was a sandy loam containing 4–6% organic matter, pH of
6.2, available P, K, Mg, Na and Ca were 52.0, 659.1, 175.2, 49.4 and
2188 mg l1, respectively. Weeds were controlled chemically using
glyphosate (Roundup; Green-Tech, Sweethills Park, Nun Monkton,
York, UK) throughout experiments. Nowatering or fertilizationwas
applied during the trials. Historically the apples annually suffered
heavily from apple scab infection. Consequently, prior to the trial
commencing in 2005 and 2006 trees were inspected in September
2004 and 2005 and only those trees with 50–80% of leaves affected,
severe foliar discolouration, and subsequent scab infection were
used in the trial. The treatments (three film forming polymers, one
fungicide and a water control) were applied in eight randomized
complete blocks with a single tree as the experimental unit, giving
a total of 40 observations per response variable. A minimal insec-
ticide program based on the residual pyrethroid insecticide delta-
methrin (Product name Bandu, Headland Agrochemicals Ltd,
Saffron Walden, Essex, UK) was applied every 2 months during the
growing season commencing in May (Nicholas et al., 2003),
a standard practice followed at the University of Reading experi-
mental site for insect pest control. All insecticide sprays were
applied using a Tom Wanner Spray Rig sprayer at 40 ml delta-
methrin 100 l1 water. Trees were sprayed until runoff, generally
1.5 l per tree.
Prior to film forming polymer sprays, polyethylene screens 2 m
high were erected around each tree to prevent dispersal of sprays
and possible cross contact with other trees and the base of the tree
. Wint. on apple cv. Golden delicious under laboratory and field conditions.
Supplier
–
er De’Songassee Swaffam Bulbeck, Cambridge CB5 0LU, UK
r/sticker De’Songassee Swaffam Bulbeck, Cambridge CB5 0LU, UK
der United Agri Products Ltd, Alconbury Weston, Huntingdon, UK
cker/wetter United Agri Products Ltd, Alconbury Weston, Huntingdon, UK
rant/desiccant GSI Horticultural, Bend, Oregon, USAcker/wetter Ciba Speciality Chemicals, Low Moor, Bradford, West Yorks,
BD12 0JZ, UK