Grape Powdery Mildew Dan OGorman: Agriculture and Agri-Food Canada,
Summerland Research and Development Centre (SuRDC)
Biology
Symptoms
Disease Cycle
Weather condition
Control
Grape Powdery Mildew
P. Sholberg
Most common and easily recognized plant diseases
Powdery mildews are usually very host specific
Requires living tissue to grow
Colonizes the surface of plant tissue and invade top layers of epidermis cells
Powdery mildews cause extensive losses in plant growth and crop yield
Grape Powdery Mildew
Two stages to powdery mildew infections: Primary and Secondary infections
Grape Powdery Mildew
https://www.agric.wa.gov.au/spring/powdery-mildew-grapevines-western-australia?page=0%2C2
https://www.agric.wa.gov.au/spring/powdery-mildew-grapevines-western-australia?page=0%2C2
P. Sholberg
P. Sholberg
Primary infection: caused by ascospores released in spring by overwintering structures called cleistothecia
Secondary infection: caused by conidia spores which can infect, develop new conidia and re-infect in a continuous cycle through the summer
Secondary infection cycles approx. every 5 to 30 days depending on the weather
Cleistothecia
Photo: Peter Sholberg AAFC
Photo: Peter Sholberg AAFC
Genera of Powdery Mildew Fungi (Drawing by C.B. Kenaga, E.B. Williams, and R.J. Green)
Powdery Mildew infection (primary and secondary)
Haustoria are specialized hyphae for nutrient absorption from the plant cells. The plant is damaged by the loss of nutrients to the fungus, disruption of photosynthesis, and premature death of leaves or other infected plant tissues
https://www.agric.wa.gov.au/spring/powdery-mildew-grapevines-western-australia?page=0%2C2
Symptoms
Observed in all succulent parts of the grapevine
Peter Sholberg AAFC
Symptoms can also be observed in late-summer, fall and winter as dark blotchy areas on dormant canes
http://seresinestate.blogspot.ca/2010_10_01_archive.html
Peter Sholberg AAFC
Symptoms
Powdery mildew affects fruit causing russeting, splitting and rotting
Peter Sholberg AAFC Peter. Sholberg, AAFC
Ascospores will colonize any fresh green tissue
Grape Powdery Mildew - Primary Infection (spring)
First signs of the disease can be observed after bud-break (early spring).
http://seresinestate.blogspot.ca/2010_10_01_archive.html
Grape Powdery Mildew- Secondary Infections (summer)
Peter Sholberg, AAFC
Mildew Disease Cycle Primary infection
period
Secondary Infection period Grapevine powdery mildew life cycle. Drawing by R. Sticht. Reproduced with permission from Compendium of Grape Diseases, 1988, American Phytopathological Society, St. Paul, MN. USA.
Effect of Temperature on the Development of Grape Powdery Mildew
Temperature of leaf*
(oC)
Days for spores to develop and infect vine parts and
produce new spores
6 32
9 25
12 18
15 11
17 7
23 6
26 5
30 6
33 oC for at least 3 days X - but 10% of spores can
recover in 5 days
40.5 oC for at least 6 hrs X - kills the fungus
Primary infection in the spring requires leaf wetness and temperature
Secondary infection in mid/late season does not require free moisture BC Ministry of Agriculture (http://www.agf.gov.bc.ca/cropprot/grapeipm)
20-30C Optimum
> 33C Stops germination
> 40C Spores die
Secondary Infection
> 10C 12-15 hrs continuous wetness
Primary Infection
temp & rain
http://www.agf.gov.bc.ca/cropprot/grapeipmhttp://www.agf.gov.bc.ca/cropprot/grapeipm
Okanagan Weather 2016
Primary infection in the spring requires leaf wetness and temperature
1. Ascospores are released in the spring after a rainfall of at least 2.5 mm
2. Infection requires at least 12-15 hours of continuous wetness at 10-15 C
> 10C 12-15 hrs continuous wetness
0
10
20
30
40
50
60
70
80
March April May June July
ave (C)
rain (mm)
https://weather.gc.ca/city/pages/bc-84_metric_e.html
Primary Infection
temp & rain
Okanagan Weather: March 2016
0
2
4
6
8
10
12
14
16
18
20
1 2 3 4 5 6 7 8
Mean Temp Definition C
Total Rain Definition mm
0
2
4
6
8
10
12
14
16
18
20
1 2 3 4 5 6 7 8
Mean Temp Definition C
Total Rain Definition mm
> 10C 12-15 hrs continuous wetness
http://climate.weather.gc.ca/climate_data/generate_chart_e.html
Primary Infection
temp & rain
Okanagan Weather: April 2016
> 10C 12-15 hrs continuous wetness
http://climate.weather.gc.ca/climate_data/generate_chart_e.html
Primary Infection
temp & rain
Okanagan Weather: May 2016
0
2
4
6
8
10
12
14
16
18
20
1 2 3 4 5 6 7
Mean Temp Definition C
Total Rain Definition mm
> 10C 12-15 hrs continuous wetness
Primary Infection
temp & rain
http://climate.weather.gc.ca/climate_data/generate_chart_e.html
Okanagan Weather 2016
Secondary infection in mid/late season does not require free moisture
20-29C optimum fungal growth (infection cycle ~5-6 days) > 33C (3 days) stops spore germination (~10% of spores can recover) > 40C (for at least 6 hrs) fungus is killed
Secondary Infection
20-30C Optimum
> 33C Stops germination
> 40C Spores die
0
5
10
15
20
25
30
35
40
March April May June July
high (C)
ave (C)
http://climate.weather.gc.ca/climate_data/generate_chart_e.html
Disease Management
Cultural Control
Remove lateral shoots in dense canopies/remove leaves in fruit zone: low light intensity favours powdery mildew development.
Use drip or micro-jet irrigation system
Control vigour: excessive vigour can lead to higher disease pressure
Variety selection: select varieties that are less susceptible to
mildew
Susceptibility of Grape Cultivars to Powdery Mildew
Susceptible Intermediate Least Susceptible
Bacchus Cabernet Franc
Cabernet Sauvignon Chancellor Chardonnay Chasselas
Gamay Gewurztraminer
Grenache Himrod
Madeleine Angevine Madeleine Sylvaner
Malbec Petit Verdot Rkatzeteli
Riesling Sauvignon blanc
Schonburger Siegerebe
Syrah Viognier
Chelois Chenin Blanc
Concord Foch
Pinot blanc Malbec Merlot Ortega
Pinot Noir Perlett
Sheridan Vidal Blanc
Weissburgunder
Auxerrois Malvoisie
Melon Pinot Gris Semillon
BC Ministry of Agriculture (http://www.agf.gov.bc.ca/cropprot/grapeipm)
Chemical control
Sulfur can be used exclusively, or in combination with DMI, strobilurin, or other classes of chemicals
Alternate between different fungicide groups to avoid fungicide resistance problems
Products like summer oils have also been shown to be good at suppressing mildew
Disease Management
://www.pinterest.com/anteekvintage/farm-collectibles/& http://ernestartist.org/June17_2011_02.htm
https://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj4w7SV_ajOAhUmxoMKHaUVCgMQjRwIBw&url=https://www.pinterest.com/anteekvintage/farm-collectibles/&bvm=bv.128987424,d.amc&psig=AFQjCNEKZ6-ZiUcXps9gVPcqJJspoJyRbQ&ust=1470441847897199https://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj4w7SV_ajOAhUmxoMKHaUVCgMQjRwIBw&url=https://www.pinterest.com/anteekvintage/farm-collectibles/&bvm=bv.128987424,d.amc&psig=AFQjCNEKZ6-ZiUcXps9gVPcqJJspoJyRbQ&ust=1470441847897199https://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj4w7SV_ajOAhUmxoMKHaUVCgMQjRwIBw&url=https://www.pinterest.com/anteekvintage/farm-collectibles/&bvm=bv.128987424,d.amc&psig=AFQjCNEKZ6-ZiUcXps9gVPcqJJspoJyRbQ&ust=1470441847897199https://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj4w7SV_ajOAhUmxoMKHaUVCgMQjRwIBw&url=https://www.pinterest.com/anteekvintage/farm-collectibles/&bvm=bv.128987424,d.amc&psig=AFQjCNEKZ6-ZiUcXps9gVPcqJJspoJyRbQ&ust=1470441847897199https://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj4w7SV_ajOAhUmxoMKHaUVCgMQjRwIBw&url=https://www.pinterest.com/anteekvintage/farm-collectibles/&bvm=bv.128987424,d.amc&psig=AFQjCNEKZ6-ZiUcXps9gVPcqJJspoJyRbQ&ust=1470441847897199
Protect grape foliage from primary infection by application of lime sulfur (dormant spray will kill the over-wintering structures) and fungicides from early shoot growth until after bloom.
Good control early in the season to prevent establishment of the disease is key to preventing a powdery mildew epidemic late
