Which Diseases of the Vine Are the Greatest Threat to Vineyards Around the World Today, and Why? Flashcards
1
Q
What organism causes powdery mildew in grapevines?
A
Powdery mildew is caused by the fungus Erysiphe necator (formerly Uncinula necator).
2
Q
Why is powdery mildew considered the most important vine disease globally?
A
It is the most widespread and economically damaging vine disease, causing significant losses in yield and fruit quality and accounting for the majority of fungicide use in major regions (e.g., $189 million in California alone).
3
Q
What are the visible symptoms of powdery mildew on vines?
A
White, powdery fungal growth on leaves, shoots, and grape clusters. Severe infection can lead to berry splitting and failure to ripen.
4
Q
Which wine regions are most affected by powdery mildew?
A
All major wine regions: California, Mediterranean Europe (France, Italy, Spain), Australia, Chile, South Africa, and also cooler regions like Germany and Oregon during dry spells.
5
Q
Does powdery mildew require rainfall to spread?
A
No. It only requires humidity—not rain—which makes it a threat even in arid regions.
6
Q
Why is powdery mildew such a concern in Australia and California?
A
Both have warm climates with moderate humidity, ideal for the fungus. Australian growers often spray 6–7 times per season; California sees annual high pressure across regions like Napa and Central Valley.
7
Q
How does powdery mildew overwinter?
A
It overwinters as spores on vine bark or in dormant buds.
8
Q
How does it spread during the growing season?
A
Via airborne spores dispersed by wind, infecting new green growth—especially under warm (20–30°C), shaded, and humid conditions.
9
Q
What is the standard chemical strategy against powdery mildew?
A
Preventative spray programs starting early in the season (~10–15 cm shoot growth) using sulfur, DMI, SDHI, and strobilurin fungicides in rotation.
10
Q
Why is fungicide rotation critical in managing powdery mildew?
A
To prevent the development of resistance. Some mildew populations have already developed reduced sensitivity to certain fungicide types.
11
Q
What cultural practices help limit powdery mildew?
A
Canopy management (to improve airflow and sunlight), timing sprays using prediction models, and experimental UV light treatment at night.
12
Q
What percentage of pesticide use in California viticulture is for powdery mildew?
A
Approximately 74%, highlighting its environmental and economic burden.
13
Q
What long-term sustainable strategy is being explored for powdery mildew?
A
Breeding and planting disease-resistant grape varieties (PIWIs) that contain resistance genes from wild Vitis species.
14
Q
What are the limitations of adopting resistant varieties?
A
Regulatory barriers, slow market acceptance, and reluctance to change traditional grape varieties in classic wine regions.
15
Q
How does climate change impact powdery mildew pressure?
A
Warmer winters increase overwintering inoculum; higher temperatures and CO₂ promote faster fungal growth. Milder winters and drought do not suppress the disease.
16
Q
Why doesn’t drought prevent powdery mildew?
A
Powdery mildew prefers relatively dry foliage with moderate humidity; unlike downy mildew, it does not require free water.
17
Q
Give an example of a region where climate change has increased powdery mildew risk.
A
Finger Lakes, New York – historically cool, now experiences hotter summers that promote mildew outbreaks.
18
Q
What causes downy mildew in grapevines?
A
A water mold (oomycete) called Plasmopara viticola.
19
Q
What are the typical symptoms of downy mildew?
A
Yellow oily spots on leaves (often called “oil spots”), white downy growth on the underside of leaves, and browning or withering of infected clusters.
20
Q
How does downy mildew damage the vine and crop?
A
It can destroy flowers and young fruit, cause defoliation, weaken vines, and reduce yield and quality. In severe cases, entire harvests are lost.
21
Q
Which wine regions are most affected by downy mildew?
A
Primarily humid and warm regions: France (especially Bordeaux and Champagne), Italy, Spain, Germany, Eastern USA (e.g., NY, Virginia), and wet-season areas in South Africa and Australia.
22
Q
What happened in Bordeaux in 2023 due to downy mildew?
A
Some growers lost up to 90% of their crop. It was the worst vintage in a decade, and the French government set up a €20 million relief fund for growers.
23
Q
How does downy mildew overwinter and spread?
A
It overwinters as oospores in soil and fallen leaves. Spring rain triggers them to release zoospores that swim and infect young tissue.
24
Q
What conditions favor downy mildew spread?
A
Leaf wetness from rain or heavy dew, plus warm temperatures (18–25°C). It spreads quickly during rainy periods — an infection cycle can repeat every 7–14 days.
25
What are the “mummies” mentioned in relation to downy mildew?
Infected berries that shrivel and harden, retaining the fungus. These serve as reservoirs for new infections.
26
What are the core components of downy mildew control?
• Preventative fungicides (especially copper-based like Bordeaux mixture)
• Systemic fungicides (e.g. mandipropamid, ametoctradin)
• Canopy management (leaf thinning, shoot positioning)
• Weather-based spray timing (using models like Plum Rules)
27
How often do growers spray for downy mildew in wet years?
Up to 8–12 times per season in extreme cases, like France 2023.
28
What are the sustainability concerns linked to downy mildew control?
• Overuse of copper can lead to soil toxicity (even though it’s organic-approved).
• Resistance to synthetic fungicides (e.g. metalaxyl) has developed due to overuse.
29
What is one long-term strategy to reduce downy mildew pressure sustainably?
Planting fungus-resistant hybrid grape varieties (PIWIs), especially in places like Germany and France.
30
How does climate change affect downy mildew risk?
It increases risk via more erratic rainfall, milder winters, and humidity spikes
31
What does the 2023 mildew crisis in Europe suggest about future risks?
It serves as a preview of viticulture under climate instability, with greater need for resistant cultivars and improved forecasting.
32
What is the scientific name of the organism that causes Botrytis bunch rot?
Botrytis cinerea
33
What are the symptoms of Botrytis bunch rot in grapes?
• In white grapes: berries turn brown and mushy.
• In red grapes: berries split and develop a velvety gray fungal growth.
• Clusters may shrivel, collapse, or leak juice, especially under damp conditions.
34
Why is Botrytis bunch rot especially damaging near harvest?
It rapidly degrades fruit quality just before picking — leading to yield loss, spoilage risks, and the need for costly sorting or early harvest.
35
What is the difference between gray rot and noble rot?
• Gray rot: uncontrolled, destructive form affecting ripening grapes in wet/humid conditions.
• Noble rot: controlled infection under specific conditions used to make sweet wines (e.g. Sauternes, Tokaji).
36
Name three regions with frequent Botrytis pressure.
Alsace, Mosel, Champagne, Oregon (Willamette), Loire Valley, New Zealand
37
Why is Botrytis less common in places like California or Chile?
These regions usually have dry summers and autumns, which do not favor Botrytis development
38
What grape characteristics increase Botrytis risk?
• Tight clusters (e.g., Pinot Noir, Zinfandel, Semillon)
• Thin skins (e.g., Riesling, Gewürztraminer)
• High humidity at harvest
39
What conditions favor Botrytis spread?
• Temperatures between 15–20°C
• Relative humidity above 90%
• Prolonged wetness (rain, dew, fog)
40
What is the most important cultural practice to reduce Botrytis pressure?
What is the most important cultural practice to reduce Botrytis pressure?
41
When are fungicides typically applied for Botrytis control?
• At flowering – to prevent early latent infections
• At bunch closure or veraison – before fruit becomes highly susceptible
42
Why is fungicide resistance a serious issue with Botrytis?
Because Botrytis cinerea has high genetic variability and has developed resistance to many single-site fungicides after only a few seasons of use.
43
What are some non-chemical alternatives being explored against botrytis?
• Biocontrols (e.g. Trichoderma, Bacillus spp.)
• Natural antifungals like chitosan or potassium salts
• Better canopy architecture and sanitation
44
What other vineyard events or pests can indirectly increase Botrytis risk?
• Hail damage
• Grape berry moth or insect feeding
• Mechanical injury
45
How does climate change affect Botrytis risk?
• Increased risk: More frequent extreme rain/humidity events near harvest
• Decreased risk: Earlier ripening in cool regions might allow harvest before Botrytis-prone weather
• Warmer climates may encourage denser canopies, increasing humidity and favoring infection
46
What are Grapevine Trunk Diseases (GTDs)?
A group of chronic fungal infections that destroy vine wood and vascular tissue, reducing vine vigor and leading to early vine death.
47
Name four major trunk diseases.
• Esca (black measles)
• Eutypa dieback (dead arm)
• Botryosphaeria dieback (black dead arm)
• Phomopsis dieback
(Also: Black Foot disease, especially in young vines)
48
What do Grapevine trunk diseases have in common biologically?
• Caused by fungi that enter pruning wounds
• Establish in woody tissue, causing cankers and decay
• No curative treatments once vines are infected
49
What is esca? What are common symptoms of Esca? (4)
A grapevine trunk disease.
• Tiger-striped leaves
• Berry spotting (black measles)
• Sudden vine collapse (“apoplexy”)
• Chronic wood decay in trunks
50
What is eutypa dieback? What are common symptoms of Eutypa dieback?
A grapevine trunk disease.
• Stunted shoots with small, tattered leaves
• Dead arms (cordon dieback)
• Reduced yield from one side of the vine
51
How do trunk diseases affect vineyard profitability?
• Lower yields year-on-year
• Premature vine death (often 5–15 years early)
• Costly replanting and lost productivity
• In CA alone, trunk diseases cause ~$260M/year in losses
52
Which regions suffer most from trunk diseases?
• France, Italy, Spain (especially older vineyards)
• California (North Coast, Central Coast)
• South Africa, Chile, Argentina (as vineyards age)
• Australia (e.g. Barossa old vines)
• All regions with vines over ~10 years old are at risk
53
Which varieties are particularly susceptible to grapevine trunk disease?
• Malbec, Semillon (Esca)
• Syrah (Botryosphaeria)
• Chenin Blanc, Sauvignon Blanc (Eutypa)
54
How do trunk disease fungi spread?
• Release airborne spores during wet weather
• Spores land on fresh pruning wounds, infecting the vine
• Infected nursery stock can also spread the disease
55
(Grapevine trunk diseases) How long can it take for symptoms to appear?
Symptoms may not appear until 8–10 years after infection. By then, internal damage can be extensive.
56
(Grapevine trunk diseases) Why are older vineyards more at risk?
• More cumulative pruning wounds
• Longer exposure to spores
• Older wood offers more entry points and is harder to protect
57
(Grapevine trunk diseases) What is delayed/double pruning and why is it used?
• Double pruning: Pre-prune in winter, then make final cuts late (e.g., just before budbreak)
• Purpose: Reduce exposure during high spore-release periods when vines are vulnerable
58
(Grapevine trunk diseases) What can be applied to protect pruning wounds?
• Fungicide pastes (e.g., benomyl, boron-based)
• Biological sealants (e.g., Trichoderma spores)
• Wound sealants (physical barriers)
59
(Grapevine disease) What is curettage and when is it used?
• A surgical method where rotted wood is cut out from the trunk using a chisel or chainsaw
• Used primarily for Esca to extend vine life
60
(Grapevine trunk disease) What is retrunking?
Training a new shoot from the base to replace a diseased cordon or trunk, giving the vine a new productive structure.
61
(Grapevine trunk diseases) What is “rogueing”?
The removal and replanting of severely infected vines when surgery is no longer viable.
62
How can vineyard design help delay GTDs?
• Training with multiple trunks
• Avoiding large cuts
• Pruning on dry, sunny days
• Selecting low-vigor systems to reduce excessive wood mass
63
Why is nursery material important in GTD management?
Infected planting stock can introduce trunk pathogens to clean sites. Hot water treatments or PCR testing help reduce this risk.
64
Are there resistant grapevine varieties to trunk diseases?
No. Most Vitis vinifera varieties are susceptible. Some resistance might come from rootstock breeding or hybrids in future, but this is not yet widely available.
65
(GTD) Why do many growers fail to act until it’s too late?
• Symptoms appear late
• Infection is invisible at first
• Cultural practices for prevention are labor-intensive and not widely adopted early enough
66
(Gtd) What long-term economic benefit has been shown with preventative measures?
Early adoption of proper pruning and wound protection can reduce GTD-related economic losses by up to 96% over a vineyard’s lifespan (Lodi, CA study).
67
What causes Pierce’s Disease in grapevines?
A bacterium called Xylella fastidiosa that clogs the vine’s xylem vessels, preventing water transport.
68
What are typical symptoms of Pierce’s Disease?
• Leaf scorch (yellow/brown margins)
• Raisined berries
• Cane dieback
• No budbreak the following spring
• Premature vine death (within 1–2 years)
69
Why is PD considered so dangerous?
It’s lethal, highly contagious via vectors, and has no cure. Affected vines must be removed. In some climates, it makes V. vinifera cultivation nearly impossible.
70
Where is Pierce’s Disease currently established?
• Southeastern USA (e.g., Florida, Texas)
• Coastal and Southern California (e.g., Temecula, Central Valley)
• Parts of Mexico, Central America
• Not yet in Europe, but high risk with climate change
71
How did PD affect the Temecula wine region in the 1990s?
An outbreak nearly destroyed the region — over 2,000 acres lost, with some growers losing 50% of their vineyard in one year.
72
Why is Europe considered vulnerable to PD?
Warming winters could make France, Italy, and Portugal hospitable to Xylella fastidiosa and its vectors — climate models show growing risk.
73
How is Pierce’s Disease transmitted?
By xylem-feeding insects, especially sharpshooters like:
• Blue-Green Sharpshooter (native to California)
• Glassy-Winged Sharpshooter (GWSS) – invasive, long-range, highly efficient
74
Can PD spread vine-to-vine without vectors?
No. It is not spread via tools or contact — only through insect feeding.
75
What is a key reason PD hasn’t yet devastated Europe?
Europe currently lacks both sustained winter warmth and the vector insects (though this could change).
76
(Pierce disease) Where else than grapevine does Xylella cause economic losses?
In olive trees in Italy, almonds, citrus, and various ornamentals worldwide — it has a broad host range.
77
What are the main methods to control Pierce’s Disease?
• Vector control (insecticides, biological control with parasitic wasps)
• Removal of infected vines
• Elimination or management of alternative host plants
• Use of PD-resistant grape varieties
78
How successful is vector control in California?
Quite successful in Napa and Sonoma, where GWSS has been largely excluded via monitoring and targeted insecticide programs.
79
What is the role of beneficial wasps in PD management?
Parasitic wasps are released to attack the eggs of sharpshooters, reducing vector population naturally.
80
Are there PD-resistant grape varieties available?
Yes. The University of California has developed PD-resistant Chardonnay and Cabernet-like cultivars via conventional breeding.
81
Why aren’t PD resistant varieties widely planted yet?
• Limited awareness and availability
• Market preference for traditional V. vinifera
• Mostly used in hotspot regions (e.g., Texas Hill Country, Temecula)
82
Are antibiotics or chemical cures available for PD?
No. Antibiotics are not legally or practically usable in vineyards. Research into vaccines and endophytic bacteria is ongoing but not yet commercial.
83
What role does winter temperature play in PD spread?
Cold winters (below ~–5°C) kill Xylella inside vines, limiting the disease to mild winter regions.
84
How is climate change altering the distribution of PD?
Warmer winters allow Xylella and its vectors to survive and spread northward or into new regions (e.g., northward shift in California and Texas).
85
What does research predict about PD in Europe?
Studies (e.g., 2024 Sci Reports) show France, Italy, and Portugal could face endemic PD within decades if Xylella and vectors are introduced.
86
What is Flavescence Dorée (FD)?
A highly contagious grapevine disease caused by a phytoplasma (a wall-less bacterium) that infects the phloem tissue of vines.
87
How is FD different from fungal or viral diseases?
• Caused by phytoplasmas, not fungi or viruses
• No curative spray exists
• Requires strict vector control and vine removal
88
What are the typical symptoms of FD?
• Yellowing (white varieties) or reddening (red varieties) of leaves
• Curling and rubbery shoots
• Incomplete lignification
• Shriveling or failure of grapes to ripen
• Severe stunting and death in young vines
89
Why is FD considered such a serious threat?
• Extremely contagious
• Can destroy vineyards in a few seasons
• Vines act as reservoirs for rapid spread
• Mandatory eradication measures required by EU law
90
Where is FD currently found?
• France, Italy, Spain, Portugal, Switzerland, Slovenia, Serbia, and others
• Worst-affected: Bordeaux, Burgundy, Veneto, Piedmont, Prosecco region
91
Is FD found outside Europe?
Not currently in commercial vineyards. The vector insect exists in Eastern USA, but the FD phytoplasma is not active there. Regions like South America, Australia, NZ are watching closely, but FD has not been detected.
92
What insect spreads Flavescence Dorée?
Scaphoideus titanus – a grapevine-specific leafhopper introduced to Europe from North America.
93
How does the vector transmit FD?
• Insects feed on infected vines and acquire the phytoplasma
• After a latent period, they become infective for life
• Transmit FD to other vines as they feed
94
Can FD spread through vineyard equipment or pruning?
No. Spread is via vectors and infected planting material, not direct contact.
95
What other phytoplasma disease looks similar to FD?
Bois Noir – causes similar symptoms but is spread by different vectors and is less aggressive.
96
What are the mandatory control measures for FD in Europe?
• Spraying insecticides (often compulsory in affected zones)
• Uprooting and destroying infected vines
• Quarantining vine material movement
• Annual field surveys and monitoring
97
How many insecticide treatments are usually required per season?
At least 2–3 treatments targeting Scaphoideus nymphs and adults.
98
Can organic or biodynamic growers avoid spraying against FD?
Rarely. In many regions, exemptions are not allowed due to the scale of risk — compliance is enforced to protect the wider region.
99
Are any grapevine varieties resistant to FD?
No. All Vitis vinifera cultivars are susceptible. Some may express milder symptoms, but infection still occurs.
100
What sustainability issues does FD management raise?
• Heavy reliance on chemical insecticides
• Conflict with organic principles and biodiversity goals
• Risk of insecticide resistance in the vector population
101
What complicates accurate FD detection?
• Overlap with Bois Noir symptoms
• Latency – vines infected late may not show symptoms until next year
• False positives/negatives unless PCR testing is done
102
How might climate change influence FD spread?
• Hotter summers and milder winters may expand the range of Scaphoideus titanus
• Cooler refuge sites (high elevation) may disappear, making FD risk more uniform
• Stressed vines from heat/drought may be more vulnerable to infection
103
What is the European control philosophy for FD?
“Find infection early, kill the bugs, rip out sick vines.” Rapid and aggressive intervention is the only effective way to contain the disease.
104
What causes Grapevine Leafroll Disease?
A group of related viruses called Grapevine Leafroll-Associated Viruses (GLRaVs) — especially types 1, 3, and 4.
105
What are classic visual symptoms of GLD?
• In red varieties: red leaves with green veins, often rolled downward
• In white varieties: yellowing leaves with green veins
• Delayed and uneven ripening, reduced vigor
106
What aspects of vine performance are affected by GLD?
• Lower sugar accumulation
• Less color and flavor in red grapes
• Smaller or fewer clusters
• Reduced yield (15–40% typical), lower wine quality
107
Does GLD kill the vine?
No, but it reduces productivity and quality over many years, often making vineyards economically unviable.
108
Is GLD a global issue?
Yes — it is present in nearly every major wine region,
109
Name three regions historically or currently battling GLD.
• South Africa (intensive replanting in the 1990s–2000s)
• New Zealand (especially Marlborough Sauvignon Blanc)
• California (Napa and Sonoma underwent major rogueing campaigns)
110
Which regions have reduced GLD successfully?
• New Zealand and South Africa, through coordinated efforts in planting clean vines and rogueing infected ones
111
How does GLD primarily spread?
• Via infected planting material
• Mealybugs and soft scale insects feeding on phloem sap
112
Can GLD spread through pruning tools or physical contact?
No. It is not transmitted by pruning or sap contact.
113
How do mealybugs spread the virus of GLD?
They acquire the virus while feeding on an infected vine and transfer it when feeding on a healthy one — often vine-to-vine along wires or bark.
114
What are the three pillars of GLD control?
1. Use of certified virus-free vines
2. Rogueing infected vines
3. Vector (mealybug and scale) control
115
What is rogueing, and when is it used for GLD?
• Identification and removal of symptomatic vines (often post-veraison)
• Used when infection is limited (<20–30%); beyond that, full vineyard replanting is often more efficient
116
What methods are used for GLD vector control?
• Insecticides (neonicotinoids, insect growth regulators, oils)
• Pheromone traps and mating disruption
• Biological control (e.g. ladybirds, parasitic wasps)
• Ant control, to prevent mealybug protection
117
How much economic damage can GLD cause?
• Up to $3 billion annually in the U.S. alone (including losses and management)
• $25,000–40,000 per hectare over 20 years
• ~20% lower Brix and major color loss in red grapes
118
Why is regional coordination important in controlling GLD?
Virus spreads easily between neighboring vineyards via mealybugs — one non-compliant grower can re-infect clean vineyards.
119
Are any varieties resistant to GLD?
No. All Vitis vinifera are susceptible.
120
What is a major challenge in GLD management?
• Asymptomatic infections
• Detection is difficult without symptoms or lab testing
• Managing vectors without harming beneficial insects
121
What causes Grapevine Red Blotch Disease?
A DNA virus called Grapevine Red Blotch Virus (GRBV), a member of the Geminivirus family.
122
What are the main symptoms of GRBD in red varieties?
• Irregular red blotches (interveinal areas)
• Green or pink veins (not rolled down like leafroll)
• Uneven berry ripening and low sugar accumulation
123
What are symptoms of GRBD in white varieties?
More subtle: light yellowing of leaves and delayed ripening, often hard to detect visually.
124
How does GRBD affect fruit composition?
• Reduced Brix (often 3–5+ points lower)
• Lower anthocyanins and flavor compounds
• Incomplete ripening, smaller berries
• Leads to lower alcohol, diluted flavor, and off-balance wines
125
Does GRBD kill vines?
No, but it is chronic and quality-degrading. Vines remain unproductive for premium wine, especially reds.
126
How did the wine industry discover GRBD?
First identified in 2012, though symptoms had been observed earlier. The virus was sequenced and classified by U.S. researchers.
127
Where is Red Blotch most common today?
• California (especially Napa, Sonoma, Central Coast)
• Oregon, Washington
• Texas, Virginia, Maryland
• British Columbia and Ontario in Canada
128
Is GRBV spread by mealybugs like leafroll?
No. Current evidence does not support mealybug transmission. The vector seems to be treehoppers.
129
What are the main pillars of Red Blotch management?
1. Certified clean planting material
2. Rogueing infected vines
3. Managing potential vector habitat (especially cover crops/weeds)
130
Are there resistant grapevine cultivars for Red Blotch?
No
