Hazards in the Vineyard Flashcards
Explain drought and its effect on the vine.
Vines need water to grow. The amount needed is a minimum of 500 mm per year in cool climates and at least 750 mm in warm regions. Lack of water causes the vine to close the stomata on their leaves in order to limit water loss. This reduces photosynthesis, if this continues the growth of the plant slows down, grape size is reduced and ripening slows down. Resulting in potentially unripe grapes and lower yields. If prolonged, vines will lose their leaves and die.
What are management options for drought?
Where allowed, irrigation systems should be considered as part of the initial design of the vineyard. Can be fitted later if the need is urgent, but can be much more difficult because of potential disruption to the vineyard for laying pipes. Some European appellations do not allow irrigation or only allow it for emergency situations (establishing young vines; drought that threatens the livelihood of growers).
If a new vineyard is being planted, drought-resistance should be high on the list of priorities in choosing a rootstock. Examples include rootstocks from V. rupestris and V. berlandieri parentage (e.g. 110R and 140R).
Choose a drought-tolerant variety such as Garnacha.
Explain excessive water and its effect on the vine.
An excess of water in summer can lead to too much vegetative growth, which can compete with grape ripening and also mean fruit is too shaded; both of which will result in less ripeness. Rainfall can also make the canopy prone to fungal diseases because of high humidity. If soils are not free draining, waterlogging may occur, reducing the amount of oxygen available to the roots, slowing down growth and eventually killing the vine. Equally, waterlogging can lead to compaction of the soils, making them difficult to work and uncontrolled water run-off.
What are management options for excess water?
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.
Explain untimely rainfall and its effect on the vine
Excess rainfall during pollination and fruit set can lead to millerandage or coulure, reducing the size of the crop and potentially also lowering quality.
Rain in mid-season can also 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).
Heavy rainfall close to vintage can lead to the grapes being swollen with water (reducing concentration of the must and with it 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 accessing the vineyard if on clay soils.
What are management options for untimely rainfall?
Nothing can be done about the incidence or amount of rainfall. However, issues such as choice of site (climate in general, slope), condition of the soil and the adequacy of drainage can mitigate some effects of untimely rainfall.
Monitoring weather forecasts: in the case of forecast of heavy/prolonged rain, winemakers may have to weigh up the options of early harvest with potentially less-ripe fruit, taking the chance on the weather improving in time for a successful later harvest or losing part or all of the crop.
Explain freeze and its effect on the vine
Fully dormant vines are relatively hardy and can tolerate quite severe frosts. However, if temperatures fall below −20°C / −4°F, the vine can be seriously damaged or even killed by winter freeze. 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). The canes or cordons are the next at risk. Frost can kill canes or cordons (reducing yield) or kill all parts of the vine above the ground, leading to the need to replace the vine.
What are management options for freeze?
Site selection
Hillside sites can be up to 5°C / 9°F warmer than the valley floor.
Vineyards near large or deep bodies of water (for example, large lakes in North America) benefit from a moderating effect.
Vines should be planted where snow settles most thickly, as a deep layer of snow protects the vine.
Choice of varieties 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.
Protecting vines
Building up soil around the vine graft (often called ‘hilling up’) is common practice in regions with cold winters, as the soil underground is only a few degrees below freezing.
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.
Vines can also be pruned to have several trunks so that those killed in winter can be replaced.
Explain frost and its effect on the vine
These occur when cold air below 0°C / 32°F collects at ground level, freezing water in the vine’s growing buds and shoots. Cold winds blowing across the vineyard after budburst are also very dangerous. If the freeze event happens to newly burst buds or young shoots that have a high-water content, it kills them. 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. If buds and young shoots are killed, the vine puts out more shoots from secondary buds (see The Anatomy of the Vine); however, these shoots are less fruitful and will take longer to ripen
What are management options for frost?
Reducing the risk
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.
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.
When frost threatens
There are several options, each of which has a cost:
Water sprinklers: 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.
Wind machines: 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). 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.
Oil or propane gas burning heaters (also known as smudge pots) and wax candles (‘bougies’) can be placed in vineyards and lit when there is a risk of frost. The disadvantages are the high cost of fuel and labour, low heating efficiency and contribution to air pollution.
Explain hail and its effect on the vine
Hailstones 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.
What are management options for hail?
Rockets may be fired into thunderclouds, seeding them with silver iodide to cause rainfall rather than hail.
In areas with regular hail storms (e.g. Mendoza), some grape growers net 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. It is therefore more appropriate in Argentina than in Burgundy.
As hail damage can be very selective, in high risk areas growers may seek to have a number of plots in different areas to ensure continuity of production.
Growers may have to consider the additional cost of crop insurance against hail.
Explain sunburn and its effect on the vine
In prolonged hot weather, sun-exposed grapes can be sunburnt. 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. There is a higher risk on vines already in a situation of water stress. 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)
What are management options for sunburn?
In designing new vineyards, row orientation and aspect can reduce the impact of the hottest afternoon sun. For example, 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.
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 sunburn.
Special agricultural sunscreen spray can be applied or the vines can be shaded with a cloth or net.
What are risks for fire and its effect on the vineyard?
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, whereas fire cannot spread through bare, cultivated soils. Damage may be to property, equipment and irrigation systems or, if severe, to the vines and their trellising. A major issue for wine quality is the smoke that these fires create.
