Page 17 - Volume 5, Issue 1, January 2012
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© Benaki Phytopathological Institute
Grape downy mildew control in organic farming
15
cation and number of applications per treat-
ment. The products tested included new cop-
per formulations with low metallic copper
(Labicuper and Glutex CU 90) and natural sub-
stances (Biplantol, Sporatec, Myco-Sin VIN,
BM-608, Stimulase). The commercial products
were used according to the manufacturer’s in-
formation. The products were compared with
an untreated control and a reference product
containing copper (standard).
Grape downy mildew assessment
The assessments were made at inter-
vals of seven days starting from the first ap-
pearance of disease symptoms until harvest.
Phenology was described according to the
Biologische Bundesanstalt, Bundessorte-
namt and CHemical industry (BBCH) scale
(3), in which grapevine phenological devel-
opment stages are described by Lorenz
et al
.
(1994) (19). Grapevine leaves and bunches
were visually assessed, 100 leaves and 100
bunches were picked randomly from the
central 10 vines of each plot. The percent-
age of leaves and bunches diseased out of
a total number assessed (disease incidence)
and the area of leaves and bunches show-
ing symptoms of disease (disease severity),
were estimated. Disease severity (infection
degree, ID) was calculated using a scale of
nine classes (0-8) using the Townsend-Heu-
berger formula (33):
I
D (%) = Σ
i
1
(
n
i
×
v
i
) /
N
×
V
where
v
i
is the damage class,
n
i
is the num-
ber in one class,
N
is the total number,
V
is
the highest class,
i
is the number of classes.
The area under disease progress curves
(AUDPC) based on disease severity was cal-
culated for each treatment according to
Shaner & Finney (1977) (29). The AUDPC was
assessed with the formula:
where
y
i
is the disease severity at the
i
th
ob-
servation,
y
i+1
is the disease severity at the
i
th
+1
observation,
n
is the total number of as-
sessments and
t
i+1
– t
i
is the number of days
between the two assessments.
AUDPC values were normalized by divid-
ing each AUDPC value by the total area of
the graph (= the number of days from the
first to last assessment of the disease × 1.0)
(13). The normalized AUDPC was referred to
as the relative area under disease progress
curve (RAUDPC).
The index effectiveness was calculated
at harvest using Abbott’s formula (1):
% effectiveness = [(
I
c
−
I
t
)/
I
c
] × 100
where
I
c
is the disease incidence of the un-
treated control,
I
t
is the disease incidence of
the treatment.
Observations for the presence of phy-
totoxic effects of all tested products were
made after each spray on the shoots, leaves,
bunches and flowers.
Yields
The effect of the investigated products
on annual production was recorded at har-
vest time. Grape yield was calculated as t/
ha/treatment.
Statistical analysis
Data in percentages were transformed
to arcsine square roots according to the for-
mula
Y
=arcsin(√(
x
%/100)) to correct normal-
ity before analysis. The data obtained were
subjected to statistical analysis using ANO-
VA, a parametric statistical method and
Tukey’s test (34) at 5% of probability. Dun-
can’s multiple range test (
P
≤ 0.05) (10) was
used to determine significant differences
among treatments in terms of grape fruit
yield. Statistics were performed with Graph-
Pad InStat version 3.00 for Windows.
Results and discussion
Environmental data
In 2010 there was high spring rainfall,
