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WsetDip D1 > 8.3 Fungal Diseases > Flashcards

8.3 Fungal Diseases Flashcards

1
Q

What is powdery mildew?

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 can also 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)
  • NOTE: 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

What species of grapes is more vulnerable to powdery mildew?

A

V. vinifera.

- American species is less vulnerable

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5
Q

Does powdery mildew affect crops other than grape vines?

A

No

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6
Q

What are the main management options for powdery mildew? Which is the preferred approach?

A
  1. Keeping an open canopy to reduce shade and the density of leaves*
  2. Applications of sulfur (prevention & treatment)
  3. Systemic fungicides

*preferred approach

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7
Q

When spraying sulphur to combat powdery mildew, when is it important to spray?

A
  • Early in the season as the disease is easier to prevent than to contain once established
  • A couple of weeks after budburst and up to véraison
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8
Q

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

A

Pro: They penetrate the green tissue, are not washed off by rain
Con: Can become resistant to some fungicides, so only a limited number of applications can be made in one year

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9
Q

What are the symptoms of downy mildew?

A
  • yellow, circular ‘oil spots’

- then white, downy fungal growth on the underside of leaves

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10
Q

In what conditions does downy mildew thrive? What are high risk periods?

A
  • Rainfall and warm temperatures (20°C / 68°F)

- Warm springs; stormy but warm summers

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11
Q

What causes downy mildew?

A

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

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12
Q

Where did downy mildew originate?

A

It was introduced from North America in the last quarter of 1800s and is now common in most wine regions

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13
Q

What are the main management options for downy mildew?

A
  1. Traditionally, sprays made from copper salts (Bordeaux mixture) (Only lasts until 20 mm of rain has fallen)
  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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14
Q

What is the Bordeaux mixture?

A
  • A combination of copper sulfate and lime

- Became the standard treatment for downy mildew in the 1880s

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15
Q

What is grey rot? What are other names for grey rot?

A
  • Botrytis cinerea
  • Botrytis bunch rot (noble 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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16
Q

What makes a grapes more vulnerable to grey rot?

A
  • If there are any points of entry (e.g. grapes having rubbed against each other in tight bunches or punctured by birds/insects)
17
Q

What varieties are particularly susceptible to powdery mildew? What varieties are particularly less prone?

A
  • More Susceptible: Chardonnay, Cabernet Sauvignon

- Less Prone: Pinot Noir and Riesling

18
Q

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

A

At harvest, the grapes are sorted and discarded

19
Q

What varieties are particularly susceptible to grey rot? Why? Name a variety that has a high level of resistance.

A
  • Semillon, Sauvignon Blanc, Pinot Noir
  • Varieties with tight bunches or thin skins
  • Resistance: Petit Verdot
20
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

21
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.

22
Q

What are the 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
  • Removing the leaves around bunches
  • Fungicides
  • Antagonistic bacteria (bacilius subtilis)
23
Q

When should fungicides be used to combat grey rot?

A

Applied at 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
24
Q

What is eutypa dieback? What is another name for this?

A

“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 tackled
25
Q

How do eutypa dieback spores spread? How does infection occur?

A
  • Spores are spread by wind over long distances

- Infection occurs through pruning wounds in moderate temperatures and especially during rain

26
Q

What varieties are particularly susceptible to eutypa dieback?

A
  • Grenache
  • Cabernet Sauvignon
  • Sauvignon Blanc
27
Q

Where has eutypa dieback become particularly prevelant?

A
  • South Australia
  • south-west France
  • parts of California
28
Q

What are the 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)
29
Q

What are the 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
30
Q

What is 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
31
Q

When is phomopsis most prevalent?

A

Years with cool and wet springs followed by humidity and moderate temperatures

32
Q

What varieties are particularly susceptible to phomopsis? What varieties are particularly less prone?

A
  • More Susceptible: Grenache

- Less Prone: Cabernet Sauvignon

33
Q

What are the 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
34
Q

What is ESCA? How does it enter the vines?

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
35
Q

What are the symptoms of esca?

A
  • Tiger-striping of the leaves

- spotting inside the wood

36
Q

In what conditions does ESCA thrive? Give 2 examples.

A

Warmer and drier climates

  1. southern Europe
  2. California
37
Q

What are the management options of ESCA?

A
  • No chemical controls
  • Sourcing disease-free stock
  • Trying new, less detrimental, pruning techniques
  • Avoid pruning in the rain
  • Removing prunings promptly from the vineyard
  • Disinfecting pruning wounds
38
Q

Name 4 other fungal diseases.

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

WsetDip D1 (87 decks)

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