Fungal Diseases Flashcards
Describe Powdery Mildew and its symptoms
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 veraison and become targets for other infections
In what conditions does powdery mildew thrive?
- optimum temps around 25C/77F
- shady conditions (dense, shady canopies)
- does not require high humidity, can thrive in dry conditions
What fungus causes powdery mildew?
Erysiphe necator (aka Oidium tuckeri)
Does powdery mildew affect crops other than grape vines?
No
Management options for powdery mildew?
- canopy management to reduce shade and the density of leaves
- applications of sulfur, for prevention and treatment
- systemic fungicides
When is best to spray sulphur to manage powdery mildew?
- early in the season to prevent the disease establishing between budburst and veraison
What is a pro and con of using systemic fungicides to combat mildews?
Pro: they penetrate the green tissue and are not washed off by rain
Cons: development of resistance can occur
Describe the cause and symptoms of Downy Mildew
Cause: Peronospera, a mold that lives within vine tissue, not on the surface
Symptoms: yellow, circular “oil spots” – then white, downy fungal growth on the underside of leaves
Management options for downy mildew?
- sprays made from copper salts (Bordeaux mixture)
- Fungicides
- Good drainage and an open canopy that dries quickly are helpful to avoid the fungus developing and spreading
Describe Bordeaux mixture?
- a combination of copper sulfate and lime
- became the standard treatment for downy mildew in the 1880s
Describe Grey Rot
- 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 (color, body, and aroma/flavor
What does the winery do with grey rot-affected grapes?
At harvest, the grapes are sorted and discarded
Varieties that are susceptible to powdery mildew?
Chardonnay
Cabernet Sauvignon
Varieties that are LESS prone to powdery mildew?
Pinot Noir
Riesling
Varieties that are more susceptible to grey rot?
- Semillon, Sauvignon Blanc, Pinot Noir
- varieties with tight bunches or thin skins
What happens if the flowers are affected with grey rot?
The fungus can stay dormant in the grape and re-emerge after veraison.
In what conditions does grey rot thrive?
The spores are typically present in the vineyard and become active in periods of rainfall and high humidity.
Management options for grey rot?
- 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)
Timing of fungicide application to combat grey rot?
Key points in the season:
- when flowering is nearly complete
- at the end of grape formation
- at bunch closure (when grapes in a bunch get large enough so that they touch eachother)
- veraison
Describe eutypa dieback.
a.k.a. Dead Arm
- a fungal trunk disease that leads to rotten wood in vines
- can affect whole vineyards
- reduces yield significantly
- kills vines over a ten-year period if not managed
Method of infection for eutypa dieback?
- spores spread by wind over long distance
- infection occurs through pruning wounds in moderate temps, and especially during rain
Varieties that are susceptible to eutypa dieback?
- Grenache
- Cab Sauv
- Sauv Blanc
Where as eutypa dieback become particularly prevalent?
- South Australia
- SW France
- California
Management options for eutypa dieback for mild cases?
- pruning late and applying fungicide to pruning wounds
- cutting back affected trunks 5-10cm beyond the visible symptoms and treated with fungicide, to burn dead wood to prevent spread
- some biological controls (e.g. Bacillus subtilis)
Management options for eutypa dieback for extreme cases?
- 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 2 years
- remove the vine and replant it
Describe phomopsis.
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
Ideal conditions to develop phomopsis?
Cool wet springs followed by humidity and moderate temperatures
Varieties that are susceptible to phomopsis?
Grenache
Varieties that are less susceptible to phomopsis?
Cabernet Sauvignon
Management options for phomopsis?
- 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
Describe Esca.
A complex fungal disease that reduces yields and leads to its death within a few years
- typically enters the vine through pruning wounds
Symptoms of Esca?
- tiger-striping of the leaves
- spotting inside the wood
- death
Ideal conditions to develop Esca?
warmer and drier climates (e.g. southern Europe, California)
Management options for Esca?
- there are no chemical treatments
- disease-free stock
- careful, gentle pruning techniques
- avoid pruning in the rain
- disinfecting pruning wounds
Four other fungal diseases?
- black rot
- black-foot disease
- bot canker
- anthracnose
