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TRANSCRIPT
Powdery mildew:
another perspective
Kathy Evans
Tas. Institute of Agricultural Research
University of Tasmania
email: [email protected]
International workshop
The research issues (powdery mildew)
• breeding vines to resist disease
• identifying susceptible tissues
– environment/viticulture influencing susceptibility
• basic pathogen biology
– How are spores produced? Inhibit spores?
• predicting disease risk
• novel control methods
This presentation
1. Observations from cool climates
2. Understanding grapevine susceptibility
3. Improving spray timing
Conducive conditions
• Young, green tissues
– new leaves, laterals, green floral parts, berries
• Low UV and high humidity
– dense and/or shaded canopies – dense and/or shaded canopies
– cloudy weather
– infection frequency high at 85% RH
• Short generation times at 20-30oC
Early season in cool climates
19th Oct.19th Oct.
EL-12
24th Nov.
EL-17
8th Nov.
EL-15, shoot
elongating rapidly
5 06 0
7 08 0
9 010 0
an(%) Inc idenceleaves(aInc idence-bunches
50
60
70
80
90
100
10%caps off: 80%
Mean
Chardonnay – no sprays
berries 4-7 mm
0
1 02 0
3 04 0
27-Nov4-Dec11-Dec 18-Dec25-Dec1-Jan 8-Jan15-Jan 22-Jan29-Jan5-Feb 12-Feb19-Feb
Dat e2004/2005
Mean(%)
Se verity-bunches
0
10
20
30
40
50
27
-No
v
4-D
ec
11
-De
c
18
-De
c
25
-De
c
1-J
an
8-J
an
15
-Ja
n
22
-Ja
n
29
-Ja
n
5-F
eb
12
-Fe
b
19
-Fe
b
Date 2004/2005
Leaves Grape clusters
Incidence
(%)
southern TasmaniaFlagshoots found Oct 22, Nov. 9
Leaf mildew
Latent period longer when cool
According to Delp (1954):
Time between spore germination and spore production.
Constant Temperature (oC)
Latent Period (days)
7 32
9 259 25
12 12
15 11
17 7
23 6
26 5
30 6
Latent period longer in vineyard
Research in New York State (Cornell Uni):• Chardonnay leaves inoculated 3 weeks after budburst
• Latent periods longer than expected
Year Average Latent Period (days)
Predicted Observed
2008 7.5 13
2009 7 9
Effect of low temperatures
• Leaves exposed for ≥ 2 h to 2-8oC had
smaller mildew colonies when inoculated
after ‘cold’ treatment
• Mortality of hyphae in young mildew • Mortality of hyphae in young mildew
colonies exposed to 2oC for 8 h
• Longer latent periods explained by
negative impact of low temperatures
Cool night temperatures
• Cool night temperatures may be lowering
mildew risk
• Radiational cooling of the leaf surface can
lead to a drastic difference from ambient air lead to a drastic difference from ambient air
temperature
Cool night temperatures
In 2005-2007, the number of days between
budburst and flowering with a minimum
temperature of 6oC was:
• Loxton, SA: 17 days• Loxton, SA: 17 days
• Hobart, Tas: 21 days
Early season in cool climates
19th Oct.19th Oct.
EL-12
24th Nov.
EL-17
8th Nov.
EL-15, shoot
elongating rapidly
Slow rates of
leaf emergence
in month after
budburst
Spray interval & shoot growth
• Very small increase in leaf area in very cool
weeks
– Fungicide effective until it decays
• Rapid leaf emergence late spring • Rapid leaf emergence late spring
– Leaves unprotected by fungicide until next spray
• Use number of leaves emerged since the
last spray to time sprays?
Chardonnay on VSP
16
20
24
ron
ind
ex
80-100%caps off
flowering imminent
4-5 leaves, inflorescence clear
berries4 mm
0
4
8
12
0 50 100 150 200 250 300 350 400 450
Degree days above 10 C
Pla
sto
ch
r
Distal shoot Medial shoot Proximal shoot
Source: Angela Smith, TIAR PhD student
Which grapevine tissues are highly susceptible to powdery mildew and what conditions
make tissues more susceptible?
Tissue susceptibility
Leaf mildew
Age-related resistance
Inoculate healthy shoot
and see which leaf has and see which leaf has
the most powdery mildew
Leaf with most mildew
Conditions for shoot
development matter
0
10
20
30
40
0 2 4 6 8 10 12 14 16 18
Dis
ease s
everity
(%
)
25oCRate of leaf emergence
2 x faster at 25oC than 18oC
Higher rate of leaf emergence:
> proportion mildewed leaves
> severity for leaf with max. 0 2 4 6 8 10 12 14 16 18
0
10
20
30
40
0 2 4 6 8 10 12 14 16 18
18oC
Dis
ease s
everity
(%
)
Leaf position
> severity for leaf with max.
mildew
Leaf position 1 ≥ 30 mm length
2.3
14.3
11.6
Spotsper cm2
Tip end of cane
Illustration of
leaf age-related
disease resistance7.3
2.3
1.0
0.3 Base of cane
disease resistance
Rust infecting
weedy blackberry
Key concept
Environment during shoot development will
affect the proportion & position of leaves with
powdery mildew
Timing important too
French researchers suggest:
Bunch mildew more severe with early leaf
infection as the leaf with most mildew will
be closer to the bunch
Leaf with most mildew
Bunch
Resistance in berries
• Berries become increasingly resistant to mildew infection from 10 days after fruit set
RieslingBerry skin with diffuse colonisation
Age-related resistance
Mildew-free Diffuse infection
Photos courtesy of D. Gadoury,
Cornell University
basalsecond
Cap fall asynchronous
basal
Photo courtesy of
D. Gadoury,
Cornell University
Capfall asynchronous
60
80
100
Capfall(%)
Chardonnay 2005, flowering = 21 days
0
20
40
22
-No
v
23
-No
v
24
-No
v
25
-No
v
26
-No
v
27
-No
v
28
-No
v
29
-No
v
30
-No
v
1-D
ec
2-D
ec
3-D
ec
4-D
ec
5-D
ec
6-D
ec
7-D
ec
8-D
ec
9-D
ec
10
-De
c
11
-De
c
12
-De
c
12 buncheson 1 vine
5 06 0
7 08 0
9 010 0
an(%) Inc idenceleaves(aInc idence-bunches
Chardonnay – no sprays
50
60
70
80
90
100
Mean
(%)
some softening7 mm4 mmberries:
0
1 02 0
3 04 0
27-Nov4-Dec11-Dec 18-Dec25-Dec1-Jan 8-Jan15-Jan 22-Jan29-Jan5-Feb 12-Feb19-Feb
Dat e2004/2005
Mean(%)
Se verity-bunches
southern Tasmania
0
10
20
30
40
9-D
ec
16
-De
c
23
-De
c
30
-De
c
6-J
an
13
-Ja
n
20
-Ja
n
27
-Ja
n
3-F
eb
10
-Fe
b
17
-Fe
b
Date 2004/2005
Bunch incidence Bunch severity
(%)
Risk index from Germany
Risk index = climate index x ‘berry resistance’ index
(W. Kast et al.)
Take home message
Spray intervals should be kept tight
• During rapid shoot growth and weather
conducive to disease
• Pre-flowering, during flowering, early fruit • Pre-flowering, during flowering, early fruit
set
Save your best materials for applications
pre-flowering to fruit set