8. Hazards, Pests and Diseases Flashcards
What are the risks of drought?
Because the vine closes the stomata to limit water loss, photosynthesis is reduced or stopped. If the situation is prolonged;
* The growth of the plant is impaired
* Grape size is reduced and ripening slows down.
* This results in potentially unripe grapes and lower yields.
* If prolonged, vines will lose their leaves and die.
What are the management options to minimise the effects of drought?
- Irrigation systems where allowed; some EU regions allow irrigation in emergency situations
- Drought tolerant rootstocks; eg rootstocks from V. rupestris and V. berlandieri parentage (e.g. 110R and 140R).
- Drought tolerant grape varieties; eg Grenache
What are the risks of excess rainfall and water?
- Too much vegetative growth; competition with grape ripening, fruit is too shaded (both leads to less ripeness).
- Rainfall leads to high humidity, therefore fungal disease pressure
- Waterlogging reduces the amount of oxygen available to the roots, slowing down growth and eventually killing the vine.
- Waterlogging can also lead to the compaction of the soils, making them difficult to work, and uncontrolled water run-off.
How can a grower mitigate the effects of excess rainfall?
If there is excess rainfall on a regular basis, then the planning of the vineyard must ensure that this issue is addressed by, where possible, planting on a slope or on free-draining soil to improve drainage, or by the construction of a drainage system
What are the risks of excess rainfall during pollination and fruit set?
Can lead to millerandage or coulure, reducing the size of the crop and potentially also lowering quality.
Why is excess rainfall in the summer a hazard?
Rain during the summer during grape ripening 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.
Why is excess water just before harvest a hazard?
Heavy rainfall close to vintage can lead to the grapes being swollen with water (reducing the concentration of the must and with it the quality of wine) and to grapes splitting, leading to grey rot. It also makes working the harvest very difficult. Examples include difficulty using mechanical harvesters or pickers accessing the vineyard if on clay soils.
How can a grower mitigate the effect of untimely rainfall?
- Choice of site (climate, slope etc).
- Condition of the soil
- Choice of whether or not to grass the land between rows of vines
- The adequacy of drainage
- Monitor weather forecasts to decide if early harvest (with potentially less ripe fruit) or taking the chance on the weather improving (risk of losing part or all of the crop).
What parts of the vine are the most at risk of winter freeze?
- The graft if it is above the surface of the ground
- Canes and cordons
What regions are most at risk of winter freeze?
Areas most affected are those with a strongly continental climate such as parts of Canada, Washington State and China.
At what temperature are vines at risk of damage by winter freeze?
-20°C and below can damage or kill vines.
What sites are desirable in areas with very cold winters and reduce the risk of winter freeze?
- Hillside sites can be up to 5°C warmer than the valley floor.
- Vineyards near large or deep bodies of water benefit from a moderating effect.
- Vines should be planted where snow settles most thickly, as a deep layer of snow can provide insulation for the vine.
Give some examples of species and varieties that can be chosen for areas at risk of winter freeze?
- Some varieties of vitis vinifera are more resilient against winter freeze than others, e.g. Cabernet Franc or Riesling.
- Some American and Mongolian vine species (V. amurensis) are extremely winter hardy, as are hybrids that have these species as a parent. For example, the Concord variety, an American hybrid, can withstand temperatures down to nearly −30°C / −22°F.
How can a grower protect vines from winter freeze?
** Building up soil** around the vine graft (often called ‘hilling up’) is common practice in regions with cold winters, as the soil helps to insulate the vine.
* Burying vines is another approach in the most extreme climates. However, this is
a very costly approach as it requires a lot of labour every year, with some Chinese regions seeing this as one of the costliest operations in the vineyard.
What are a growers options to mitigate the effects of very cold winters (winter freeze?
- Site selection
- Choice of grape variety
- Protecting the vines (building up or burying).
How do frosts occur?
Frosts occur when cold air below 0°C collects at ground level, freezing water in the vine’s growing buds and shoots.
Why are warm areas vulnerable to spring frosts?
Warmer areas are vulnerable because the vine begins to grow and will be damaged if there is a drop in temperature.
How does the vine react if young buds and shoots are killed?
the vine puts out more shoots from secondary buds; however, these shoots are less fruitful and will take longer to ripen, which can itself be a problem (more likely to be affected by rain or autumn frost).
What are the two types of frosts?
- Advective
- Radiative
What are advective frosts?
Advective frosts are caused by large volumes of cold air moving in from very cold areas.
What are radiative frosts?
Radiative frosts are the 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 will allow a layer of freezing cold air to develop just above the surface of the soil.
As cold air is denser than warm air, this freezing cold air will collect in valley bottoms.
How can a grower reduce the risk of frosts?
- In site selection, care must be taken to avoid frost pockets and to choose hillside sites where cold air can drain away.
- Delaying pruning postpones budburst into warmer months. If buds at the end of canes get frosted, they can be removed.
- Choosing a variety that buds late, such as Riesling, can help.
- Vines trained high off the ground offer more protection, as the coldest air is near the
ground.
Having bare soil between the vines (rather than a cover crop) absorbs more heat during the day and radiates this heat during the night.
What are a grower’s options when a frost threatens a vineyard?
- Water sprinkers (aspersion)
- Wind machines
- Oil or propane gas burning heaters and wax candles
What is aspersion and how does it work?
Water sprinklers to combat frost
* 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.
What is the only method that can combat against advective frosts?
Water sprinklers (aspersion)
How do wind machines combat frosts?
These large fans, which are 4–7 m high, pull warmer air from above down to ground level, thereby raising the temperature. These are effective where there is an inversion layer, a warm zone of air 10 m above the ground (+3–5°C / 5–9°F).
What are the costs associated with aspersion?
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.
What are the costs associated with wind machines?
One study has found that the investment in wind machines is warranted if there is a chance of a damaging radiation frost once every five years.
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.
What are smudge pots and bougies?
Smudge pots; Oil or propane gas burning heaters
Bougies; Wax candles
Can be placed in vineyards and lit when there is a risk of frost.
What are the disadvantages of smudge pots and bougies?
The high cost of fuel and labour, low heating efficiency and contribution to air pollution.
Smudge pots; oil or propane gas burner heaters
Bougies; wax candles
What are the strategies to minimise the risk or damage of hail?
- Rockets
- Netting
- Owning several plots
- Crop insurance
How do rockets prevent hail?
Rockets may be fired into thunderclouds, seeding them with silver iodide to cause rainfall rather than hail.
What needs to be considered before implementing netting for hail protection?
As netting creates some shading, this solution can only be used where there are high sunlight levels. It is therefore more appropriate in Argentina than in Burgundy.
How do grapes become sunburnt?
In prolonged warm, sunny weather, grape transpiration is much more limited, and therefore less effective, than leaf transpiration. As a result, grapes can reach higher temperatures than the leaves and become burnt.
How does sunburnt affect grapes?
- Sunburn leads to scars on the skin of the grape and, in extreme cases, to the eventual death of the grapes.
- Sunburn has a negative impact on grape quality. Browning of the grape, a bitter taste, and increased susceptibility to rot (due to skin damage).
How can growers reduce the risk of sunburnt grapes?
- In designing new vineyards, row orientation and aspect can reduce the impact of the hottest afternoon sun.
- The amount of direct sun exposure can be adjusted through canopy management techniques. Growers may choose to partially shade the fruit zone in hot regions.
- If a heatwave is forecast, additional irrigation, where allowed, may be applied to reduce water stress and, hence, the chance of sunburn.
- Special agricultural sunscreen spray can be applied or the vines can be shaded with a cloth or net.
What factors make a vineyard more susceptible to fire damage?
Vineyards that are near woodland, pastures or other crops may be more at risk as they provide fuel for the fire. Cover crops and organic mulches can also provide fuel
How can growers prepare their property if a fire threatens?
- Installing fire detectors and sprinklers
- Installing and maintaining a water tank
- Providing employee training for action in the event of an emergency.
How does smoke affect grapes and wine?
Aroma compounds in smoke can be absorbed by the grapes. Once in the grape these compounds often bind with sugars and form aroma-less precursors.
Similar to other aroma precursors in the grapes, these compounds then only become aromatic through the fermentation process. The strength of the aroma can increase during the ageing of wine and during bottle ageing as further aroma precursors break down and become aromatic.
What are the management options against smoke taint?
- Affected musts can be tested analytically and/or by micro-vinifications (to release the smoke aromas) in the days leading up to harvest to establish the extent of the problem.
- As it is thought that the smoke aroma precursors are present on the inside of the skin of grapes, how the grapes are handled can reduce the effect of smoke taint. Hand harvesting, gentle or whole bunch pressing, lower fermentation temperatures and reduced maceration times can reduce the uptake of the compounds.
- Flash détente and reverse osmosis can also help, but will not remove the taint completely.
- Blending with unaffected wine
What are the most important climactic hazards?
- Drought
- Excess water
- Untimely rainfall
- Hail
- Frost
- Winter Freeze
- Sunburn
- Fire
- Smoke taint
How does phylloxera affect the vine?
This aphid-like insect feeds and lays eggs on the roots of grapevines.
Phylloxera harm vines by damaging the roots, reducing the uptake of nutrients and water. The damaged roots are also vulnerable to additional attack by bacteria and fungi. These attacks lead first to a weakening of plants (reducing growth and yield) and then to the death of the vines.
How does phylloxera spread?
The insects can spread through crawling but are most commonly transported by humans, for example, on the roots of young vines, in soil, on equipment such as leaf trimmers and harvesters and by irrigation water
What are the symptoms of a phylloxera infestation in the vineyard?
- Vines die of drought in patches that increase in size year by year
- Vine roots are covered with the insects surrounded by yellow eggs
- Swellings on older roots
- Pale green leaf galls on the under-surface of the leaves
- Slow, stunted shoot growth and leaf yellowing appears in around three years, the plant dies after around five years.
What soils inhibits phylloxera?
Sandy soils
Which American vine species provide the most protection against phylloxera?
V. berlandieri, V. riparia and V. rupestris
What fungal disease are these grapes affected by?
Powdery mildew
What fungal disease is this vine affected by?
Downey mildew
