Grape vine is one of the orchard, horticultural crops which
adds much of the export income to the country as
commercial fruit crop and also as one of the healthy
dietary food to the people.
Such a crop, which is a boon to the growers is facing threat
with few important diseases like powdery mildew, downy
Am going to present on the topic grape vine powdery
mildew symptomology and management
• The fungus, Uncinula necator, is found mostly on
the leaves and fruit stems, but it will also infect
green fruit in some seasons.
• Affected berries have a dull, darkened
appearance and are usually covered with the light
powdery growth of the fungus.
• In some varieties new fruit infection will cease as
the sugar content rises and the fruit matures.
• Infection on leaves appears conspicuously on the
upper sides as white, powdery patches.
• Later, the entire surface of the leaves may be
covered with the fungus.
• They turn an ash grey colour and quickly
become covered in spores
• When infection is severe, the leaves will
scorch or turn brown and fall.
• When grape cluster stems become covered
with the fungus the stems shrivel and
considerable losses from shelling of the fruit
• Black specks of the overwintering spore-
forming bodies can be seen in the older
• Infection usually starts soon after the
Weather conducive to disease development
Leaves: The first powdery mildew lesions are
frequently found on the undersides of leaves
(a). As the epidemic progresses, lesions become
apparent on the upper sides of leaves as well.
These lesions will increase in size and number if the
disease is left unchecked.
Severely infected leaves may become brittle and drop
off. Starting as early as late July, very small orange
to black spherical structures called cleistothecia
develop on the upper and lower surfaces of leaves
Powdery Mildew Symptoms
The first powdery mildew lesions are frequently found on the
undersides of leaves
• (b). Shoots: Brown to black irregular
blotches that can measure up to a few
centimetres, follow the gradual
degeneration of the fungus over the
course of the season
• (c). The spots have indistinct margins and
remain visible even following shoot
Very small orange to black spherical structures
called cleistothecia develop on the upper and
lower surfaces of leaves
• Inflorescences and rachis: Usually seen on
rachis, powdery mildew has the
appearance of a grey to whitish powder.
• Severe infections of the rachis can result
in clusters being dropped, especially if
mechanical harvesting is done.
• Symptoms on the rachis are similar to
those on shoots
• The gradual degeneration of the fungus over
the course of the season
Berries: Berries can be infected from immediately after
bloom through 4 weeks post-bloom.
They turn an ash grey colour and quickly become covered in
(d), giving them a floury appearance. At the end of the
season, cleistothecia also appear on the berries
(e). Affected berries dry out and may drop off
(f). Berries that infected later during the period of
susceptibility are prone to splitting, making them
susceptible to infection by Botrytis.
Cracking of the fruits
• Affected berries dry out and may drop off
• E. necator is an obligate parasite of grapevines,
i.e., it can develop only on living grapevine tissue.
• In our climate, E. necator overwinters as
cleistothecia, structures containing ascospores (or
• In the spring, the ascospores mature and infect
the leaves growing in proximity to bark.
• Following infection, spots covered with asexual
• The conidia of E. necator do not need free
water on the tissue to infect it.
• However, high relative humidity
promotes germination of the conidia and
• Powdery mildew of grape is promoted by
hot (optimum temperature of 25°C), dry
(but humid) weather since water inhibits
germination of the conidia.
• Cleistothecia also appear on the berries
Effect of temperature on the
development of grape powdery
Temperature of leaf*
Days for spores to develop and
infect vine parts and produce
33 (for at least 3 days) 0 (but 10% can recover in 5 days)
40.5 (for at least 6 hrs) 0 (kills the fungus)
Severe powdery mildew infection on
'Chancellor' grape leaf, with
Spore (condia) production of powdery
mildew on a grape leaf.
Powdery mildew cleistothecia on
Circinate structures of fungus
magnified under microscope
(cleistothecium and ascus
• clean cultivation of vines or destruction
of all diseased parts.
• Grow resistant varieties etc.
• Prophalactic spray with bordeaux mixture
1% or lime sulphur before onset of
monsoon i.e., before the onset of
• Manage canopies to increase air drainage
and light penetration by removing lateral
shoots in dense canopies. If necessary
remove leaves in the fruiting zone. Dense
canopies provide low light intensity,
which favours powdery mildew
• Use an under-vine irrigation system (drip
• Manage irrigation carefully. Excessive
Dusting of vines with 300 mesh sulphur.
• 1st dusting when shoots are 2 weeks old.
• 2nd dusting prior to blossoming.
• 3rd dusting when fruits are half ripe.
• Spray :oxythioquinox (morestan) @ 0.03%
at 4 days interval starting from last week
of december to 1st week of march.
Timing Fungicide Sprays:
• Protect grape foliage from primary
infection by application of fungicides
from early shoot growth until after
bloom. Good control early in the season
to prevent establishment of the disease is
the key to preventing a powdery mildew
epidemic later in the summer.
• Apply fungicides such as Kumulus
(sulphur), Nova, Lance, Pristine, Sovran,
• When new growth is 5 to 10 cm long.
• Just before or immediately after bloom.
• Every 10 to 14 days until grapes begin to
soften and red varieties begin
development of color and white varieties
change from green to white or yellow. If
Kumulus (sulphur) is used, shorten the
spray interval to 7-10 days.
Group1 Rate/ha Rate/acre PHI2 (days) Notes
U8 750 g 300 g 14
Apply at 14-21
interval for high
or rapid growth
phases. Do not
apply more than
13 300 ml/ha 122 ml/acre 14
on a 14 day
interval. Do not
preventively using a
14-21 day interval. Do
not use Flint or other
group 11 fungicides
more than 2 times per
season. Alternate with
fungicides from other
groups. See Fungicide
fungicide. Apply at 14-21-
day intervals. Do not use
Sovran or other group 11
fungicides more than 2
times per season.
Alternate with fungicides
from other groups. See
• Otherwise: if a farmer cannot recognise
at early stages…
It is recommended to go for a spray with
Wettable sulpur @ 0.2 %
karathane @ 0.07%
• Grape varieties: Monitor susceptible varieties.
• When: Start looking for powdery at about 3-5 leaves and
continue throughout the season.
• Where: Throughout the vineyard.
• How: Monitor for the appearance of discolored spots that
turn whitish on the upper and lower leaf surfaces.
Do not confuse with pesticide residues.
When checking, change the angle of the
The whitish spots are particularly visible
when the leaf is held at an approximately
Be sure to sample leaves from the interior
of the canopy since disease development
is favored by shade.