Biology and Control of Powdery Mildew on Grapes

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Biology and Control of Powdery Mildew on Grapes
James W. Travis Professor of Plant Pathology
Grape Extension Specialist
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Penn State Grape Disease Research and Extension
Team
Investigators J. W. Travis, R. Crassweller, N.
O. Halbrendt, B. Hed Research Assistants J.
Rytter, E. Anderson, B. Jarjour, K.
Wholaver Students B. Gugino, PhD, F. Westover,
MS Penn State F. R. E. C. Penn State L. E. G.
R. E. C. 290 University Drive Erie,
PA Biglerville, PA 17307 [phone]
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Powdery Mildew The Most Important Disease of
Grapes
Affects all cultivated grapes, every season,
wherever they are grown Affects all green
tissues of the vine Can cause severe economic
damage
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Powdery MildewBiology/Disease Cycle
Fungus, Uncinula necator over-winters on
bark Primary infection cycle
- Ascospores
released during spring rain (0.1 rain,
budbreak to fruit set)
- blown to emerging tissue - can
infect wet or dry tissue at gt50F.
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Disease Cycle of Powdery Mildew, Uncinula
necator (Schw.) Burr.
fungus overwinters in dormant buds
infected buds give rise to young infected
shoots
ascus with ascospores
cleistothecium
spores are released in spring
developing buds become infected
conidia
cleistothecia are produced on leaves, shoots
berries in late summer
fungus on leaves, shoots and berries produces
conidia that are spread by wind
spores infect green tissues
illustration adapted from R. Sticht
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Powdery MildewBiology/Disease Cycle
Secondary (summer) cycles spores (conidia) from
primary infections wind dispersed Rainfall not
required for release or infection Generation
time dependent on temperature only 5-7 days
under ideal conditions (60-80F)
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To manage powdery mildew on leaves, shoots, and
rachises, Know that...

• Tissues are susceptible all season
• Older tissues are more resistant
• Early season infections provide inoculum
• to developing flowers/fruit
• Mid-late season infections
• Sensitive hybrids and vinifera may need
  protection until veraison

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Powdery Mildew Pre-bloom ScoutingImprove your
skills in disease control
Look for leaf and rachis infections - the
presence of powdery mildew just millimeters away
from flowers and young berries places them at
very high risk Observing powdery mildew on
cluster stems before bloom has been associated
with severe fruit disease epidemics.
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Symptoms and Signs

• Powdery mildew infects all green tissues of
  grapevine

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Symptoms and Signs
Reduced photosynthesis in infected leaves
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Symptoms and Signs - leaves
Grayish-white powder on upper (sometimes lower)
surface
Cupping, yellowing, leaf drop
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Symptoms and Signsrachis
infections at bloom can cause poor fruit set
Grayish-white powder on surface
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Symptoms and Signscanes
brown patches on the surface of dormant canes
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Symptoms and Signs - cluster infection may result
in

• poor fruit set
• crop loss
• reduced juice quality

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Berries are susceptible to infection until the
sugar content reaches 8
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Symptoms and Signs fruit
Split berries/rot complex organisms
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Symptoms and Signs fruit
Infected purple or red cultivars may fail to
color properly resulting in off-flavored wine
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In late summer, spherical bodies, Cleistothecia,
form on the surface of infected leaves, shoots
and berries
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powdery mildew on Vidal
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Early incidence of powdery mildew on Chancellor
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Late season powdery mildew
Chancellor
Concord
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Do not mistake Powdery Mildew infection with
Downy Mildew
Downy
Powdery
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Downy Mildew
early berry infection
cluster infection
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Downy Mildew
leaves
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Chancellor
Downy Mildew
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Systemic downy mildew shoot infection
Chancellor
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Powdery Mildew Management
Chemical Control
Is dependent on spring rainfall,
temperature, amount of disease last season,
variety
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Powdery Mildew Management
Chemical Control
REMEMBER control is critical from immediate
pre-bloom through fruit set - peak of fruit
susceptibility !!! Use...

• Best materials
• Full rates
• Best coverage
• Tighter intervals

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Powdery Mildew Management
Chemical Control
Whats available

• Strobilurins Flint, Sovran, Abound
• very effective
• broad spectrum
• very prone to development of resistance (rotate,
  full rates, good coverage, limit of sprays,
  dont use as last spray of season)
• SI Nova, Elite, Rubigan, Procure
• efficacy has slipped due to resistance
• still important in rotations

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Powdery Mildew Management
Chemical Control
Whats available
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Powdery Mildew Management
Chemical Control
Alternatives

• Serenade
• formulation of soil bacterium (Bacillus subtilis)
• fair/good control in rotations with SIs and
  strobies
• good results with Serenade/Sulfur combination
• organic certification

• JMS Stylet Oil
• effective at 14 day intervals, 1.5-2 solution
• Good coverage critical
• 2 or more applications around veraison lowers
  brix
• organic formulation available

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Powdery Mildew Management
Chemical Control
Alternatives

• Nutrol (Monopotassium phosphate)
• apply post-infection little or no protective
  activity
• more effective when applied weekly at half rates
  than biweekly at full rates
• moderate efficacy
• inexpensive
• good coverage critical
• organic certification
• Kaligreen, Armicarb (Potassium bicarbonate)
• similar to Nutrol, but may be more expensive

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Cultural Control
Powdery Mildew
Maximize air circulation and sun
exposure Trellis system Planting site Row
orientation
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Disease Management
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Disease Management
Resistant Cultivars

• Select resistant cultivars
• Native American grapes more resistant/tolerant to
  powdery mildew
• Vitus vinifera and French hybrids are susceptible
  to the fungus

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Relative Cultivar Susceptibility to Powdery
Mildew

• Variety Susceptibility
• Baco Noir
• Cabernet Franc
• Cabernet Sauvignon
• Cayuga White
• Chambourcin
• Chancellor
• Chardonel
• Chardonnay
• Concord

Variety Susceptibility DeChaunac
Foch Gewurztraimer
Merlot Pinot Noir
Reisling Seyval
Vidal
Vignoles
slightly susceptible or sensitive
moderately susceptible highly
susceptible 2004 NY PA Pest Management
Recommendations for Grapes
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Disease Management
Preventative Cultural Practices Good air
circulation in the vineyard Site Selection
Slope/Aspect (N-S) Avoid low spots Wooded
borders
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Preventative Cultural Practices
Plant Row Spacing/Orientation Narrow row
spacing/less air circulation Close plant spacing
results in less air circulation and denser
canopy higher RH less sun light exposure
easier for disease to spread from plant to
plant Plant Nutrition High vigor denser canopy
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Preventative Cultural Practices
Reducing Canopy Density Vigor management,
nutrients, cropping Pruning Shoot
thinning Cluster thinning Leaf pulling
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Preventative Cultural Practices
Not Practical To Reduce source of
over-wintering inoculum Prune infected shoots
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Use of Protectant Fungicides
Chemical Control
From 3-5 inch shoot growth on V. vinifera and
French hybrids
Not delayed beyond immediate prebloom stage of
any cultivar
2 or 3 prebloom applications on highly
susceptible cultivars Critical period for
managing fruit infection
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excellent good control
moderate
Fungicides for Powdery Mildew
Copper
Sulfur

• Copper, Sulfur
• Oil
• Quinoxysen

JMS Oil Stylet
Quintec

• Sterol Inhibitors
• Strobilurins

Bayleton
Nova
Rubigan
Procure
Elite
Sovran
Flint
Abound
Pristine
2004 NY PA Pest Management
Recommendations for Grapes
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Fungicides for Powdery Mildew

• Fungicides Control Rating
• Strobilurin
• Abound may cause injury on apple
• Sovran may cause injury on sweet cherry
• Flint may cause injury on Concord
• Pristine Buscalid may cause injury on
  Concord
• Sterol inhibitor (SI)
• Rubigan
• Procure
• Elite
• Nova
• Bayleton resistance is widespread
• Protectant
• Copper
• JMS Stylet Oil Petrol./Biologicals-Eradica
  nt
• Sulfur may cause injury on Concord red
  hybrids
• Quintec

2004 NY PA Pest Management Recommendations
for Grapes
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Powdery Mildew Infection Periods 2003 2004
FREC, Biglerville, PA
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Take Home Message
Early fungicide sprays reduce the number of
leaves that become infected
Later sprays reduce severity of infections that
slip through
Can have serious fruit disease in mid summer
consequence of events during early stages of
fruit development, e.g., rainy weather and /or
spray program problem
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Take Home Message
Manage fungicide resistance Alternate
fungicides with different modes of action
poor spray coverage low rates on susceptible
tissues poor control increased resistance
development