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.
