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Grapevine Powdery MildewErysiphe necator
Doug Gubler Department of Plant Pathology University of CaliforniaDavis CADavis, CA
Powdery MildewErysiphe necator
Disease epidemiology/ Pathogen biology--Sunlight Pathogen negatively effected by direct sunlight (UV) Reduces sporulation, spore germination, infection and lesion
expansion
Sonoma County Vineyard Technical Group 5-19-2016
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Grapevine Powdery Mildew
Effects of Moisture Optimum RH is 65%
No effect of higher RH
Effect of RH is overcome by temperature i.e. temperature more important.
Free water has negative effect on conidial sporulation, infection and lesion expansioninfection, and lesion expansion.
2 mm or more of rainfall required for ascospore release at temperatures of 70-85 F
Free water has positive effect on ascospore germination
Powdery mildew epidemics Grapevine powdery mildew epidemics are driven primarily by
temperatures in the canopy. When temperatures are between 70° and 85° F the pathogen
can reproduce (spore to new spores) as rapidly as every five p ( p p ) p y ydays (Delp 1954).
Between 90° to 92 F, the fungus grows at a slower pace with the time required to reproduce being 15 days.
At higher temperatures, a further reduction in spore production, germination, and infection occurs.
Open canopies are detrimental to growth and survival of the pathogen; due to temperature and ultraviolet p g ; pradiation.
Sonoma County Vineyard Technical Group 5-19-2016
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Overwintering--Bud Perennation
Occurs on same vines each year Flag and monitor Remove flag shoot(s) and treat that vine and the 4
around the infected vine with Rally+JMS Stylet Oil, Inspire Super or Luna Experience
Protect next year’s buds during 3-6 leaf stage. Infection next year should be expressed at the Infection next year should be expressed at the
same time as infection occurred this year i. e. if infection started during the formation of the 3rd leaf then that leaf will show disease next year. This allows the prediction of when the spray application should be made.
Sonoma County Vineyard Technical Group 5-19-2016
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Bud Perennation
Overwintering--Chasmothecia
Form in late summer and fall. Chasmothecia wash from leaves with fall and
winter rains onto cordons, canes, and spurs. Spores released with rainfall, sprinker irrigation,
dew Monitor for disease 7-10 days after ascospore
release lower surface of basal leavesrelease—lower surface of basal leaves.
Sonoma County Vineyard Technical Group 5-19-2016
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Sonoma County Vineyard Technical Group 5-19-2016
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Effect of High Temperatur > 92F
Negative effect spore production
Negative effect on lesion expansion
Negative effect on spore germination
Negative effect on infection process
Cessation of Spore Production
R2 = 0.84
R2 = 0.68R2 = 0 88
75
100
ng
Sp
ore
s
R2 = 0.59
R = 0.88
R2 = 0.94
R2 = 0.70
R2 = 0.92
R2 = 0.88
0
25
50
% C
olo
nie
s P
rod
ucin
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0 5 10 15 20 25
Duration of Temperature, hr
Figure 8. The effects of temperature and duration on cessation of E. necator spore production. Primary data were obtained as described for Figure 7. Colony survival was calculated for each leaf, each isolate, averaged for each duration, and plotted with linear regression trend lines. In order to obtain reasonable x-axis intercepts, only 1 zero value was used if consecutive zero values occurred; consecutive values of 100% were similarly truncated. Room temperature controls (22.5º C) were all 100% (data not shown).
Sonoma County Vineyard Technical Group 5-19-2016
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Two Potential Outcomes with multiple exposure to high temp
“Loss of “Acclimation”Growth
Loss of biological function”
Acclimation
TimeTime
Fungicide Resistance
Resistance to DMI’s !
Resistance to Strobilurins ?
Sonoma County Vineyard Technical Group 5-19-2016
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Resistance Management
Aim- Reduce Selection pressure to prevent further b ild f i ibuildup of resistant strains.
Should not use within class of chemistry for mixes or alternations i.e. NEVER DMI-DMI or Strob-Strob
Do not stretch intervals unless you know what the level of disease pressure is (UCDRI)level of disease pressure is. (UCDRI)
Spray coverage is as important as the product you use.
Coverage! Coverage! Coverage!
Sonoma County Vineyard Technical Group 5-19-2016
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Early Season Powdery Mildew Control
Budbreak applications = 95% control at disease onset. Micronized S 5#/A in 100 gal water/A (above
temperature of 22-23 C)
JMS Stylet Oil 1-2 % in 100 gal water/A
Purespray
Rally + Topsin M as a delayed dormant Powdery mildew and canker control
Combating Overwintering Resistance
Make sure the first application each year is NOT A DMI (Rally, Elite, Metal, Procure, etc.) OR Strobilurin ( Abound, Sovran, Flint, Pristine
Use multisite products first (Oil, df Sulfur, Dormant Lime Sulfur)Dormant Lime Sulfur)
Sonoma County Vineyard Technical Group 5-19-2016
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Powdery Mildew
Model Use
Allows stretching of spray intervals under low to intermediate disease pressure.
Shorten spray intervals under high disease pressure Organic products should be used on 5‐7 day interval under high disease pressure with the exception of JMS Stylet Oil which can be used on 14 day interval under high pressure.
Sulfur dust use stretched to 30 day intervals using the RI model in California and Germany.
Gubler-Thomas Risk Index, Courtland CA. 2007
100
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ler-
Tho
mas
PM
Ris
k In
dex
0
10
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pr
27-A
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ay
11-M
ay
18-M
ay
25-M
ay
1-Ju
n
8-Ju
n
15-J
un
22-J
un
29-J
un
Date in 2007
Gub
l
Sonoma County Vineyard Technical Group 5-19-2016
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Gubler‐Thomas PM Risk Index 2010
120
30
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30 30
40
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40
60
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30 30
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90
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100100100100100
90
100100100100
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100100100100100100100100100100
90
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100100100100100100100100100100100
90
100100100100
90
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RISK ASSESSMENT IN
DEX
000
20
30
20
30
20
10
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30
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20
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30 30
20
10
0
20
0
20
Gubler‐Thomas PM Risk Index 2011
120
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40 40 40
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100100100100100100
80
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100100100
80
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100100
80
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120
RISK ASSESSMENT IN
DEX
000000000000
20
30
20
30
10
20
30
10
0000
20
30
20
000000000000000
20
30
20
0
20
0
20
30
0
20
Sonoma County Vineyard Technical Group 5-19-2016
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Gubler‐Thomas PM Risk Index 2012
40
60
80
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70
60
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100100
90
80
70
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100100100100
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100100100100100100
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50
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90
40
60
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100
120
RISK ASSESSMENT IN
DEX
00000
20
30
0
20
Gubler‐Thomas PM Risk Index 2013
40
60
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40
30 30
50
70
90
100100100
80
90
100100100100100100100100
80
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100100100100100
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40
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4040
60
80
100
120
RISK ASSESSMENT IN
DEX
00
20
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20
30
20
10
30
20
30
20
30
20
30
20
30
20
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20
Sonoma County Vineyard Technical Group 5-19-2016
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Gubler‐Thomas PM Risk Index 2014
100100100100100100100100100100 100100100100100 100 100 100
80
90 90 90
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30 30
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70
Risk ASSESSMENT In
dex
30 30 30
20
10
0000
20
30
20
10
30
Effect of Dormant or Delayed Dormant Treatment on viability of Ascospores—Vineyard Trial
Treatment Rate % Germ % w/Appressoriaw/Appressoria
Micronized S 5# 2 0 JMS Stylet Oil 2% 1 0 Lime Sulfur 10 g 1 0 Rally/Topsin 5oz+1.5# 0 0** LS+JMS Oil 2+10 0 0LS JMS Oil 2 10 0 0 Citricide 2% 33 4 Untreated---- 30 6**Also effective for canker disease
Sonoma County Vineyard Technical Group 5-19-2016
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Fungicide Application: Rally + Topsin MPowdery Mildew & Canker Disease Control
Early season pathogen Early season pathogen detectiondetection Monitoring for disease
Spore trapping
Bioindication
Sonoma County Vineyard Technical Group 5-19-2016
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Severity of infection is dependent on: cultivar how early disease onset occurs
21‐30°C 5 days30‐33°C 15 days>33°C greatly reduced
21‐30°C 5 days30‐33°C 15 days>33°C greatly reduced
Powdery Mildew of GrapevinesPowdery Mildew of Grapevines
weather conditions
Timed fungicide applications are in most cases necessary to manage the disease
high costs resistance of E. necator to QoI and DMI documented
>33°C greatly reduced>33°C greatly reduced
Integrated Pest Management Integrated Pest Management monitor the presence of the pathogen in the vineyard use of forecasting epidemiological models
Powdery Mildew Spore Trapping
Sonoma County Vineyard Technical Group 5-19-2016
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Spore density X Disease severity
90
100
y= 10.4 + 0.0007396x – 0.00000000226(x‐15110)2
R2 = 0.48n = 43
20
300
4
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Disease severity (%)
0
10
20
0 5.0E+04 1.0E+04 1.5E+05 2.0E+05 2.5E+05
Estimated spore density/week
Sonoma County Vineyard Technical Group 5-19-2016
