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Grape Powdery Mildew
Dan O’Gorman: Agriculture and Agri-Food Canada, Summerland Research and Development Centre (SuRDC)
• 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
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)
20-30°C Optimum
> 33°C Stops germination
> 40°C Spores die
Secondary Infection
> 10°C 12-15 hrs continuous wetness
Primary Infection
temp & rain
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
> 10°C 12-15 hrs continuous wetness
0
10
20
30
40
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60
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80
March April May June July
ave (⁰C)
rain (mm)
https://weather.gc.ca/city/pages/bc-84_metric_e.html
Primary Infection
temp & rain
Okanagan Weather: March 2016
0
2
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16
18
20
1 2 3 4 5 6 7 8
Mean Temp Definition °C
Total Rain Definition mm
0
2
4
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1 2 3 4 5 6 7 8
Mean Temp Definition °C
Total Rain Definition mm
> 10°C 12-15 hrs continuous wetness
http://climate.weather.gc.ca/climate_data/generate_chart_e.html
Primary Infection
temp & rain
Okanagan Weather: April 2016
> 10°C 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
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16
18
20
1 2 3 4 5 6 7
Mean Temp Definition °C
Total Rain Definition mm
> 10°C 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
• 20-29°C – optimum fungal growth (infection cycle ~5-6 days) • > 33°C –(3 days) stops spore germination (~10% of spores can recover) • > 40°C – (for at least 6 hrs) fungus is killed
Secondary Infection
20-30°C Optimum
> 33°C Stops germination
> 40°C Spores die
0
5
10
15
20
25
30
35
40
March April May June July
high (⁰C)
ave (⁰C)
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
• 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 later in the summer.
Key timing for Powdery Mildew infection (and spray applications):
Disease Management
Dormant – New growth (5-10 cm) – Bloom (pre or post) –> –> –>
For more information on the UC Davis powdery mildew forecasting models: http://www.ipm.ucdavis.edu/DISEASE/DATABASE/grapepowderymildew.html
Powdery Mildew Disease Forecasting
• University of California, Davis model is the most widely available mildew model
• Can be used to help time fungicide applications
• Works well in California and has helped reduce the number of fungicide applications on grapes
• Unfortunately the UC Davis model has limitations in British Columbia
- The model only works for predicting the secondary infections in BC
• There are two parts to the model to align with the two different infection periods of the pathogen (primary and secondary infections)