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WSET 4 (Unit1) - Hazards, Pests and Diseases > Fungal Disease > Flashcards

Fungal Disease Flashcards

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1
Q

Describe Powdery Mildew and its symptoms.

A

Fungal disease that attacks young, green parts of the vine

  • Starts as dull grey patches and become black patches as they advance
  • Patches can damage young shoots, inflorescences and grapes, reducing yield.
  • Grapes do not ripen
  • Grapes can split at véraison and become targets for other infections
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2
Q

In what conditions does powdery mildew thrive?

A
  • Optimum temperature around 25°C (77°F)
  • Shady conditions (dense, shady canopies)
  • Does not require high humidity, can thrive in dry conditions.
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3
Q

What fungus causes powdery mildew?

A

Erysiphe necator (aka Oidium tuckeri)

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4
Q

Does powdery mildew affect crops other than grape vines?

A

No

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5
Q

Management options for powdery mildew.

A
  1. Canopy management to reduce shade and the density of leaves
  2. Applications of sulfur (prevention & treatment)
  3. Systemic fungicides
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6
Q

When is best to spray sulphur to manage powdery mildew?

A

Early in the season to prevent the disease establishing Between budburst and véraison.

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7
Q

What is a pro and con of using systemic fungicides to combat mildews?

A

Pro: They penetrate the green tissue and are not washed off by rain

Cons: Development of resistance can occur

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8
Q

Describe the cause and symptoms of Downy Mildew.

A

Cause: Peronospora, a mould that lives within vine tissue, not on the surface

Symptoms: yellow, circular ‘oil spots’ - then white, downy fungal growth on the underside of leaves

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9
Q

Management options for downy mildew?

A
  1. Sprays made from copper salts (Bordeaux mixture)
  2. Fungicides
  3. Good drainage and an open canopy that dries quickly are helpful to avoid the fungus developing and spreading
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10
Q

Describe Bordeaux mixture?

A
  • A combination of copper sulfate and lime
  • Became the standard treatment for downy mildew in the 1880s
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11
Q

Describe Grey Rot

A
  • Botrytis cinerea or Botrytis bunch rot
  • A fungus that can cause significant damage to fruit: loss of yield and drop of quality in the wine (colour, body and aroma/flavour)
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12
Q

What does the winery do with grey rot-affected grapes?

A

At harvest, the grapes are sorted and discarded.

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13
Q

Varieties that are susceptible to powdery mildew.

A

Chardonnay, Cabernet Sauvignon

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14
Q

Varieties that are less prone to powdery mildew.

A

Pinot Noir and Riesling

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15
Q

Varieties that are more susceptible to grey rot.

A
  • Semillon, Sauvignon Blanc, Pinot Noir
  • Varieties with tight bunches or thin skins
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16
Q

What happens if the flowers are affected with grey rot?

A

The fungus can stay dormant in the grape and re-emerge after véraison.

17
Q

In what conditions does grey rot thrive?

A

The spores are typically present in the vineyard and become active in periods of rainfall and high humidity.

18
Q

Management options for grey rot.

A
  • Selecting grape varieties that have small grapes with thick skins
  • Protecting the grapes against other pests (which could split skins)
  • Keeping an open canopy
  • Leaf stripping around bunches
  • Fungicides
  • Antagonistic bacteria (bacilius subtilis)
19
Q

Timing of fungicide application to combat grey rot.

A

Key points in the season:

  1. when flowering is nearly complete
  2. at the end of grape formation
  3. at bunch closure (when the grapes in a bunch get large enough so that they touch each other)
  4. véraison
20
Q

Describe eutypa dieback.

A

Otherwise known as Dead Arm

  • A fungal trunk disease that leads to rotten wood in vines
  • Can affect whole vineyards
  • Reduces yields significantly
  • Kills vines over a ten-year period if not managed
21
Q

Method of infection for eutypa dieback.

A
  • Spores spread by wind over long distance
  • Infection occurs through pruning wounds in moderate temperatures and especially during rain
22
Q

Varieties that are susceptible to eutypa dieback.

A
  • Grenache
  • Cabernet Sauvignon
  • Sauvignon Blanc
23
Q

Where has eutypa dieback become particularly prevalent?

A
  • South Australia
  • South-west France
  • California
24
Q

Management options for eutypa dieback for mild cases?

A
  • Pruning late and applying fungicide to pruning wounds
  • Cutting back affected trunks 5-10 cm beyond the visible symptoms and treated with fungicide (burn dead wood to prevent spread)
  • Some biological controls (e.g. Bacillus subtilis)
25
Q

Management options for eutypa dieback for extreme cases.

A
  • Retrain the vine from a sucker (a shoot that grows from the base of the vine) left on the trunk; results in a loss of yield for two years
  • Remove the vine and replant it
26
Q

Describe phomopsis.

A

A fungal disease that causes a reduction in crops:
- Infected canes whiten and break off easily
- Shoots growing from these canes develop brown cracks at their bases
- Leaves are also affected

27
Q

Ideal conditions to develop phomopsis

A

Cool wet springs followed by humidity and moderate temperatures.

28
Q

Varieties that are susceptible to phomopsis.

A

Grenache

29
Q

Varieties that are less susceptible to phomopsis.

A

Cabernet Sauvignon

30
Q

Management options for phomopsis.

A
  • Fungicides applied three weeks after budburst and then again every two weeks if wet conditions continue
  • Diseased wood should be removed and burnt
  • Prune early or late
  • Do not prune in rainy weather
31
Q

Describe Esca.

A

A complex fungal disease caused by a group of organisms that reduces yields and leads to its death within a few years

  • Typically enters the vine through pruning wounds
32
Q

Symptoms of Esca.

A
  • Tiger-striping of the leaves
  • Spotting inside the wood
  • Death
33
Q

Ideal conditions to develop Esca.

A

Warmer and drier climates Southern Europe California.

34
Q

Management options for Esca.

A
  • There are no chemical treatments
  • Disease free stock
  • Careful gentle pruning techniques
  • Avoid Pruning in the rain
  • Disinfecting pruning wounds
35
Q

Four other fungal diseases.

A
  1. Black rot
  2. Black-foot disease
  3. Bot canker
  4. Anthracnose

WSET 4 (Unit1) - Hazards, Pests and Diseases (6 decks)

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