Level 4 D1 Chap 8 - Hazards, Pests and Diseases Flashcards
Question
Answer
What are the physiological changes in a vine during water stress?
- Leaf stomata close to reduce transpiration and limit water loss, which also reduces gas exchange.
- Photosynthesis is reduced as CO2 levels fall.
- Vegetation growth and grape ripening reduce.
- Prolonged periods result in leaf loss and death of the vine.
How can water stress be managed?
- Irrigation systems, where laws allow.
- Drought resistant rootstock (e.g. 110R and 140R).
- Drought tolerant grape variety (e.g. Garnacha/Grenache)
What does an excess of water cause?
- Vegetative growth results in shaded grapes, reducing ripeness.
- Increased risk of fungal disease.
- Waterlogged roots can impact growth and kill the vine, and lead to compacted soil
How can an excess of water be managed?
Primarily in vineyard selection and design:
plant on slopes;
plant in free draining soil;
construct drainage systems
What are the two worst times in the season for heavy rain?
- During pollination and fruit set - it can result in millerandage and coulure.
- At harvest grapes can swell and split - diluting must, and potentially causing grey rot and oxidation.
How can heavy rain at harvest be managed?
Trade off from bringing the harvest forward, or risking damage to the crop from rain.
What climate types and/or geographical locations are most at risk from vine death in freezing temperatures?
Strong continental climates: e.g. Canada, Washington State, parts of China
How can vine death from freezing be managed?
- Plant on hillside rather than valley floors.
- Plant near bodies of water to benefit from temperature moderation.
- ‘Hilling up’ soil around the vine graft
- Burying the vine over winter
- Prune multiple trunks to increase chances of survival
When is frost the biggest risk to a vine?
During budburst, frost can kill the buds and young shoots, leaving growers reliant on secondary buds. These have lower yields and delayed ripening.
How can frost risk be minimised?
- Plant late budding varieties (e.g. Reisling)
- Avoid planting in frost pockets
- Leave bare soil between vines to absorb more heat in daytime to reflect back overnight
- Late winter pruning can delay budburst
- Train vines high
When frost is imminent, how can the risk be minimised?
- Aspersion – Water sprinklers freeze around plant can capture latent heat in plant, but must be kept on until temperatures rise. Requires irrigation system. This is the ONLY method for advective (wind) frost.
- Wind machines (4-7 meters high / helicopters - work if there is an inversion layer @ 10m. This is typically radiation frost. Investment is warranted if used once every five years.
- Burners (smudge pots) - although these are polluting
How can the risk of hail be minimised?
- Mainly netting, although this can shade grapes so can only use when sunlight is high / strong.
- Multiple plots spreads risk - hail is often localized
- Rockets can be fired into thunderclouds seeding them with silver iodide to cause rainfall
- Crop insurance against hail.
How can the risk of fire be minimised?
- Install fire detectors & sprinklers.
- Have water tank on site
- Provide employee training on action to take in case of emergency.
Not planting next to woodlands or other crops helps mitigate as does cultivation between rows of vines.
What can be done about smoke taint?
Smoke taint is thought to be concentrated in the skin:
- Before harvest, test analytically or by micro-vinification
- MINIMIZE SKIN IMPACT in fermentation
- Hand harvest
- Whole bunch pressing
- Lower fermentation temperature
- Reduce maceration
Flash détente and reverse osmosis will help but not remove completely.
Can blend with unaffected wines.
What animal pests can attack vines and what is the primary defence against each?
Phylloxera - resistant rootstock Nematodes - resistant rootstock Grape moths - chemicals (insecticide, or pheromones) Spider mites - pesticides Birds - netting Mammals - fencing
List at least 4 fungal diseases
Powdery mildew Downy mildew Grey rot Eutypa Dieback Phomopsis Esca
What diseases are the most prevalent vine diseases, which attack young, green parts of the vine
Powdery mildew and downy mildew
How can powdery mildew be prevented and/or treated?
Prune an open canopy to minimise shade
Early spraying of sulphur
Systemic fungicides
How can downy mildew be treated?
Bordeaux mixture - copper sulphate and lime
Other fungicides
Good drainage and open canopy
What fungus attacks fruit and which species are particularly vulnerable?
Grey rot
Species with tight bunches or thin skins:
- Semillon, Sauvignon Blanc, Pinot Noir
How can grey rot be treated?
- Prune an open canopy
- Fungicides - takes repeated applications and risks resistance
- Competing bacteria (Bacillus subtilise)
- Plant varieties that have small grapes & thick skins
________ infects pruning wounds and results in rotten wood
Eutypa dieback (also called Dead arm)
How can eutypa dieback be treated?
- Prune late and apply fungicide to wounds
- Cut back dead wood 5cm past infection * burn the wood
- Cut away plant and regrow from a sucker
What are the 2 main vine bacterial diseases?
Pierce’s disease
Grapevine yellows
How are bacterial infections spread?
They need a vector
Pierce’s disease is the sharpshooter
Grapevine yellows is the leafhopper
What are the 2 main vine viruses?
Leafroll virus
Fanleaf virus
How are viral infections spread?
Either with a vector, or grafting infected material
Fanleaf vector is the dagger nematode
Leafroll vector is the mealy bug
_____ causes vines to grow twisted and stunted
FANLEAF VIRUS causes vines to grow twisted and stunted
How would you identify leafroll virus in a vineyard?
Primary impact:
- Slow growth &
- Slow ripening
Because of that:
- High acid, low color and sugar in grapes
- Yields halved
In autumn:
- Leaves change colour in the autumn (red or yellow)
- Downward rolling of leaves in autumn
How would you identify fanleaf virus in a vineyard?
Stunted, twisted vines
What factors influence harvest timing?
- Climate
- Sugar levels - minimum alcohol levels may need to be reached
- Forecast of rain
- Aroma and tannin ripeness (usually determined by taste)
- Wine style - e.g. later for botrytis, or off dry styles.