8.1 Hazards

Question 1

Name the 9 main hazards.

Answer 1

1. Drought
2. Excess of Water
3. Untimely Rainfall
4. Freeze
5. Frosts
6. Hail
7. Sunburn
8. Fire
9. Smoke Taint

Question 2

What is the minimum amount of water vines need per year in cool climates?

Answer 2

500 mm per year

Question 3

What is the minimum amount of water vines need per year in warm climates?

Answer 3

750 mm per year

Question 4

What happens when vines do not get enough water?

Answer 4

• Vine will close the stomata on their leaves to limit water loss.
• Reduces photosynthesis
• Slows growth and ripening
• Reduces grape size
• Lower yields, unripe grapes
• Leaf loss, death

Question 5

What could happen in regions that depend on irrigation if drought continues over several years? Give an example of where this has happened.

Answer 5

• Water may become so scarce that the use of water for irrigation is not allowed
• Entire vineyards can be lost
• Example: Olifants River region of South Africa

Question 6

Name some management options for drought.

Answer 6

1. Irrigation systems
2. drought-resistance should be high on the list of priorities in choosing a rootstock
3. Choose a drought-tolerant variety

Question 7

Name a drought-tolerant variety.

Answer 7

Garnacha

Question 8

Name a drought-resistance rootstock.

Answer 8

rootstocks from V. rupestris and V. berlandieri parentage

e.g. 110R and 140R

Question 9

Why could an excess of water become a hazard?

Answer 9

- Too much vegetative growth
Which leads to:
1. Competition with grape ripening 
2. Fruit is too shaded
3. Less ripeness

• High humidity
  Which leads to:
  1. Fungal diseases
• Poor drainage, waterlogging
  Which leads to:
  1. Prohibits oxygen from getting to the roots
  2. Slows growth
  3. Can kill the vine
  4. Difficult to work / uncontrollable water run off

Question 10

Name some management options for excess of water.

Answer 10

• planting on a slope
• planting on free-draining soil
• construction of a drainage system

Question 11

What could happen if there is excess rainfall during pollination and fruit set?

Answer 11

• millerandage or coulure
• reducing the size of the crop
• potentially lowering quality

Question 12

What could happen if there is excess rainfall during the mid-season? Why?

Answer 12

• Can reduce the rate of ripening of fruit.
• Mild water deficiency before véraison reduces the growth of shoot tips, allowing the grapes to ripen more satisfactorily.

Question 13

What could happen if there is heavy rainfall close to the vintage?

Answer 13

• Grapes swollen with water (reducing the concentration of the must and with it the quality of wine)
• Grapes splitting (grey rot)
• Makes harvest very difficult (difficulty using mechanical harvesters, accessing the vineyard if on clay soils)

Question 14

Name some management options for untimely rainfall.

Answer 14

Mitigation:

• Choice of site (climate in general, slope)
• Condition of the soil
• adequacy of drainage
• Monitoring weather forecasts (early harvest)

Question 15

Below what temperature can the vine can be seriously damaged or even killed by winter freeze?

Answer 15

−20°C / −4°F

Question 16

What part of the vine is most at risk from winter freeze? What is second?

Answer 16

1. If vines are grafted onto rootstock, the graft is the part of the vine that is most at risk (if it is above the surface of the ground).
2. Canes or cordons

Question 17

What types of climates are most affected by freeze? Give 3 examples.

Answer 17

• Strongly continental climates

- Examples: Canada, Washington State, China

Question 18

Name 3 very general management options for freeze.

Answer 18

1. Site selection
2. Choice of varieties
3. Protecting vines

Question 19

Describe 3 decisions made during site selection to combat freeze.

Answer 19

1. Hillside sites can be up to 5°C / 9°F warmer than the valley floor.
2. Vineyards near large or deep bodies of water benefit from a moderating effect.
3. Vines should be planted where snow settles most thickly, as a deep layer of snow protects the vine.

Question 20

What decisions go into choosing grape varieties to plant to combat freeze? Give examples.

Answer 20

• Some varieties are more resilient against winter freeze than others
• e.g. Cabernet Franc or Riesling.
• Some American (e.g. Concord can withstand temperatures down to nearly −30°C / −22°F) and Mongolian vine species (V. amurensis) are extremely winter hardy, as are hybrids that have these species as a parent.

Question 21

Describe 3 methods of protecting vines from freeze.

Answer 21

1. “Hilling Up” - Building up soil around the vine graft as the soil underground is only a few degrees below freezing.
2. Burying vines - Very costly approach as it requires a lot of labour every year (China)
3. Vines can also be pruned to have several trunks so that those killed in winter can be replaced.

Question 22

How does frost occur?

Answer 22

When cold air below 0°C / 32°F collects at ground level, freezing water in the vine’s growing buds and shoots.

Question 23

When could frosts be most deadly to the vines? Why?

Answer 23

• In spring during budburst

- If the freeze event happens to newly burst buds or young shoots that have a high-water content, it kills them

Question 24

What climates are prone to frosts? Why?

Answer 24

• Wide range
• Cool climate areas are vulnerable though the vine responds to regular low temperatures by not growing until a mean air temperature of 10°C / 50°F is reached.
• Warmer areas are vulnerable because the vine begins to grow and will be damaged if there is a drop in temperature.

Question 25

What are the two types of frosts?

Answer 25

1. Advective frosts | 2. Radiative frosts

Question 26

What is an Advective frost?

Answer 26

Caused by large volumes of cold air moving in from very cold areas

Question 27

What is a Radiative frost?

Answer 27

- Result of heat being lost on still, cool nights. - The earth is heated by the sun during the day and releases it during the night. - The amount of heat lost depends on the level of cloud cover. - Windless nights allow a layer of freezing cold air to develop just above the surface of the soil. - Cold air is denser than warm air, this freezing cold air will collect in valley bottoms.

Question 28

What 5 actions can be taken to reduce the risk of frost?

Answer 28

1. In site selection, care must be taken to avoid frost pockets (places where cold air collects) and to choose hillside sites where cold air can drain away. 2. Delaying pruning postpones budburst into warmer months. If buds at the end of canes get frosted, they can be removed. 3. Choosing a variety that buds late, such as Riesling, can help. 4. Vines trained high off the ground offer more protection, as the coldest air is near the ground. 5. Having bare soil between the vines (rather than a cover crop) absorbs more heat during the day and radiates this heat during the night.

Question 29

When frost threatens, what 3 actions can a grape grower take to mitigate the effects?

Answer 29

1. Water sprinklers (also known as aspersion) 2. Wind machines 3. Oil or propane gas burning heaters and wax candles

Question 30

How does water sprinkling combat frost? What costs are associated with this method?

Answer 30

- Sprinklers installed - As water freezes around the parts of the plant, it releases latent heat, protecting the plant - The system must be kept on until the temperature rises - The costs are for the equipment and for the water. The running costs can be much lower than wind machines or heaters, although not if the cost of water is high

Question 31

How do wind machines combat frost? What costs are associated with this method?

Answer 31

- Large fans, 4–7 m high, pull warmer air from above down to ground level, thereby raising the temperature. - Effective where there is an inversion layer, a warm zone of air 10 m above the ground (+3–5°C / 5–9°F). - The initial investment is considerable. - Helicopters can be used to create the same effect. They are expensive, but may be worth it if the risk is severe but short term.

Question 32

How do heaters combat frost? What costs are associated with this method?

Answer 32

- Placed in vineyards and lit when there is a risk of frost. - high cost of fuel and labour - low heating efficiency - contribution to air pollution

Question 33

What is hail?

Answer 33

pellets of frozen rain

Question 34

How can hail damage a vine?

Answer 34

- Can damage and rip young shoots and leaves. - Ripening grapes can both be damaged and become a point of entry for botrytis and other diseases. - Yields can be seriously reduced in the first and following seasons. (If the damage is caused early in the season, the vine may be able to reshoot from existing buds.)

Question 35

Name 2 regions that suffer from hail repeatedly.

Answer 35

Argentina, Burgundy

Question 36

Name 4 management options for hail.

Answer 36

1. Rockets may be fired into thunderclouds, seeding them with silver iodide to cause rainfall rather than hail. 2. Netting the fruit zone of the vines to protect ripening grapes. As netting creates some shading, this solution can only be used where there are high sunlight levels. 3. Seek to have a number of plots in different areas to ensure continuity of production. 4. Growers may have to consider the additional cost of crop insurance against hail.

Question 37

Why is sunburn bad for grapes?

Answer 37

1. Scars on the skin of the grape and, in extreme cases, to the eventual death of the grapes 2. Lowers grape quality - browning of the grape - a bitter taste - increased susceptibility to rot (due to skin damage)

Question 38

How does sunburn occur? In what climates is there a higher risk?

Answer 38

- In prolonged hot weather, sun-exposed grape have limited grape transpiration; less effective than leaf transpiration - Grapes can reach higher temperatures than the leaves and become burnt - There is a higher risk on vines already in a situation of water stress.

Question 39

How are sunburnt grapes typically removed?

Answer 39

Through sorting

Question 40

What are 5 management options for sunburn?

Answer 40

1. Row orientation and aspect can reduce the impact of the hottest afternoon sun. 2. Canopy management techniques to adjust the amount of direct sun exposure. Growers may choose to partially shade the fruit zone in hot regions. 3. If a heatwave is forecast, additional irrigation, where allowed, may be applied to reduce water stress and sunburn. 4. Special agricultural sunscreen spray can be applied 5. Vines can be shaded with a cloth or net.

Question 41

How can row orientation reduce the impact of the hottest afternoon sun? Describe where this is used.

Answer 41

In hot regions in the Northern Hemisphere, east-west row orientation should be avoided so that grapes on the south side of the row are not subject to day-long sun and to intense afternoon sunshine.

Question 42

Where is fire a hazard? Name 3 regions.

Answer 42

- In hot and dry countries - Vineyards that are near woodland, pastures or other crops - Cover crops and organic mulches - Australia, California and Chile

Question 43

What are 3 ways wineries and vineyards in areas that are prone to fires can prepare their property?

Answer 43

1. Installing fire detectors and sprinklers. 2. Installing and maintaining a water tank. 3. Providing employee training for action in the event of an emergency.

Question 44

Why is smoke taint a hazard? When does this become a problem for the grapes?

Answer 44

- ‘Smoky’ or ‘plastic’ aromas in the final wine - The effect on fruit increases in the period from véraison onwards. - These compounds only become aromatic through the fermentation process. - The strength of the aroma can increase during the ageing of wine and during bottle ageing

Question 45

Name 4 management options for smoke taint.

Answer 45

1. Tested analytically and/or by micro-vinifications in the days leading up to harvest 2. Hand harvesting, gentle or whole bunch pressing, lower fermentation temperatures and reduced maceration times can reduce the uptake of the compounds. 3. Flash détente and reverse osmosis can also help, but will not remove the taint completely. 4. Winemakers may be able to rescue affected wines by a combination of these measures and by blending with unaffected wines.