Powdery Mildew and Botrytis
Prepared for VIGGA
By Stephen Eng
June 19,2002
The Disease Triangle
Conventional Farming
Key Concept of Organic and
- Disease Prevention
- Built-in Defenses
- Optimum Environment
- Good Sanitation
- Rotate Crops
- Good Cultural Practices
- Natural Poisons
Integrated Pest Management
- a systematic decision making process
that supports a balanced approach to a
crop production system
Elements of an IPM System
1. Planning and Managing system to prevent insects,plant diseases and weeds.
2. Identify pests, enemies and damage.
3. Monitor pests and beneficials and environmental conditions.
4. Make control decisions based on potential damage, cost, crop value, impact on other pests, impact on beneficials and on the environment.
5. Use multiple strategies such as mechanical, biological, chemical and cultural.
6. Evaluate effects and efficacy.
Powdery Mildew
"mild-climate, dry weather disease"
Symptoms
1. Infected tissues show a whitish gray, dusty or "powdery" appearance ( powder is mycelium with conidiaspores and conidia ).
2. Infected cluster stems become brittle and may break.
3. Infected clusters before bloom may lead to poor fruit set.
4. Berries are susceptible until sugar level reaches 8%, although established infection continues until 15% sugar content.
5. Berries may split, dry up or rot before they reach full size.
Powdery Mildew, Disease Cycle
1. Fungus overwinters as thin threads called hyphae inside dormant buds or as cleistothecia ( small black bodies) on fallen leaves, buds, bark , canes and left-over fruit.
2. Fungus is active just before budbreak, spores are released and continue for about 6 weeks until bloom and are spread by rainfall and warmer weather ( 68-80 F optimal).
3. Early infection is not always noticeable but the infection to new spore development period may be as little as 5-6 days.
4. Rainfall can reduce fungus development.
5. Low diffuse light favours disease development.
Powdery Mildew, Infection Period
Temperature at Leaf ( C) Days to spore development, infection and new spore development
6C - 32 days
9 - 25
12 - 18
15 - 11
17 - 7
23 - 6
26 - 5
30 - 6
33 - ( >3 days) 0 ( but some recovery after 5 days)
40.5 - (>6 hours) 0 ( kills fungus)
Powdery Mildew, Cultural Control
1. Shaded and sheltered areas favours disease.
2. Plant less susceptible varieties.
3. Improve drainage- wet areas favours disease
4. Canopy Management- sunlight inhibits fungus.
5. Air Drainage- open canopies.
Chemical Control
Product Rate/ha Rate/a Timing PHI
Sulphur WP 2.5 kg Pre 4.5-6 Post 1.0 kg Pre 1.8-2.5 Post As needed 30*days
Kumulus DF 3.5 kg 1.4 kg As needed 30*days
Nova 200 g 85 g 21 days 14 days
Powdery Mildew Chemical Control Schedule
Order Crop Stage Product
1st- Dormant Lime Sulphur
2nd- New Growth 5-10 cm Kumulus
3rd- Just before Bloom Kumulus
4th- After Berry Set before ¼ size Nova or Kumulus
5th- Berries ½-full size Nova or Kumulus
6th- Berries softening and changing colour Nova
7th- Post Harvest Bordeaux 3-6-1000
Note on Sulphur- Fungicidal activity is associated with vapour phase. Optimal temperature is 74-86F.
Not effective below 64F. Less effective in humid vs. dry air.
Note on Bordeaux- 3-6-1000 = 3 kg Copper Sulphate or Fixed Copper+6 kg Hydrated Lime+ 1000L water/ha. Fixed Copper is less injurous to plants than Copper Sulphate.

Bunch Rot - Botrytis Cinerea " wet weather disease"
Bunch Rot, Smptoms
Time Suseptible Parts Description
Early Spring Buds, young shoots Turn brown, dry up
Before Bloom Leaf Large, irregular, reddish-brown necrotic patches
Before Bloom Inflorescence Rot, dry up, fall off
End Bloom Stalk ( pedicel) Clusters below wither and die
Veraison Grapes Infected directly through wounds or epidermis. Berries dry up or burst in wet weather.
Bunch Rot, Disease Cycle
· Not specific to grapes.
· Overwinters on canes, bark and dormant buds.
· Spores active in spring between 1-30C ( 18C optimal) and begin infecting various plant parts if RH > 90%.
· After infecting fruit during the blossom period, the fungus remains inactive ( low sugar, high acid ) and is active again as the berries soften ( 5-8% at veraison) and continues as they ripen.
· Spores are spread from cluster to cluster by wind or summer rains, irrigation, heavy dew, or juice from split berries.
Bunch Rot Infection at Various Temperatures
Temperature ( C ) Time for Infection ( slow drying or high RH )
10 C - 30+ hr
15.5 - 18+
23.5 - 15+
26.5 - 22+
30 - 35+
Bunch Rot, Cultural Controls
· Sanitation-remove and or bury
· Irrigation- vigour and humidity
· Canopy Management-air circulation,spray efficacy.
· Nutrition- avoid " excessive" vegetative growth; excess N lessens berry skin resistance to fungal infections.
· Loose clustered and thick-skinned varieties are less susceptible.
· Control Powdery Mildew
· Prevent bird and insect damage.
Bunch Rot, Chemical Controls
Timing Treatment Rate/a PHI Notes
5% Bloom Rovral 600 g 30 days* Not more than 2X
After bloom Elevate 460 g 7 days Not more than 3X
Veraison Rovral 600 g 30 days*
3 weeks before harvest Elevate 460 g 7 days
Organic Fungicides
· Baking Soda - 0.5% Solution
· Sulphur - Kumulus is the commercial product
· Lime Sulphur
· Bordeaux Mixture
· Solarization