Hazards Flashcards
Explain drought and its management options?
Vines need water to grow and to produce good quality fruit at yields that make grape growing financially viable. The amount needed is a minimum of 500 mm per year in cool climates and at least 750 mm in warm regions. A lack of water causes the vine to close the stomata on their leaves in order to limit water loss. This reduces photosynthesis. If this situation continues, the growth of the plant slows down, 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.
In regions that depend on irrigation, if drought continues over several years, water may become so scarce that the use of water for irrigation is not allowed. As a result, entire vineyards can be lost (for example, in the high volume Olifants River region of South Africa).
Management options
- Where it is allowed, irrigation systems should be considered as part of the initial design of the vineyard. They can be fitted later if the need is urgent, but this 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 excess rainfall and its management options?
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.
Management options
- 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 the effects of untimely rainfall and its management options?
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 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 accessing the vineyard if on clay soils.
Management options
- 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 the effects of freeze and its management options?
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.
Areas most affected are those with a strongly continental climate such as parts of Canada, Washington State and China.
Management options
In areas with regularly very cold winters, growers have several options:
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 the effects of frosts and its management options both to reduce the risk as well as when frost threatens?
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. The damage done and the impact on yields can be enormous, and in frost-prone regions growers go to great lengths to minimise this risk.
Vines in a range of climates are vulnerable. 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; 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, autumn frost).
Management options
There are several options for the grower where frost is an issue. These can be divided into actions that seek to reduce the risk of frost and those that seek to combat the hazard if frost does strike.
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 (also known as aspersion): if the vineyard already has an irrigation system, then sprinklers can be used or installed specially for frost protection. 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). One study has found that the investment in wind machines is warranted when there is a 20 per cent chance of a damaging radiation frost in any one year. 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 the effects of hail and its management options?
Hail, pellets of frozen rain, can cause severe damage to vines at various stages of development. 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. The occurrence of hail is unpredictable in general, although some regions (parts of Argentina, Burgundy) have suffered repeatedly.
Management options
There are strategies for hail protection in use:
- 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 what a sunburn is and list its management options?
Vines need sunlight for photosynthesis, which then enables vines to ripen grapes. However, 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) have all been cited as potential issues. Therefore, sunburnt grapes typically need to be removed by sorting, which reduces yields.
Management options
- 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.
Explain the effects of fire and its management options?
Fire is a serious hazard in hot and dry countries. Warmer, dryer weather associated with climate change has seen an increase in the incidence of fires. Parts of Australia, California and Chile have suffered in recent years. Fires may occur outside of human control and therefore are often difficult to prevent. However, 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.
Management options
Wineries and vineyards in areas that are prone to fires can prepare their property by:
- Installing fire detectors and sprinklers.
- Installing and maintaining a water tank.
- Providing employee training for action in the event of an emergency.
Explain smoke taint and its management options?
Smoke in the vineyard during the growing season can result in ‘smoky’ or ‘plastic’ aromas in the final wine. The effect on fruit increases in the period from véraison onwards. 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).
Management options
- 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 (and hence what action may be needed).
- 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 (Macerations using Heat in Crushed Fruit Fermentations) and reverse osmosis can also help, but will not remove the taint completely.
Winemakers may be able to rescue affected wines by a combination of these measures and by blending with unaffected wines.
What are pests?
Pests are organisms that harm the vine and impact the production of grapes in a negative way. Some compete for water or nutrients, while others directly attack the vine and/or grapes, affecting yield and quality. Grape growers have to evaluate the seriousness of the attack and decide whether measures need to be taken. This includes an evaluation of the economic cost of actions taken in relation to the potential damage.
Some major pests and diseases are the result of insects or fungi being imported from one territory where the vine species have natural resistance to those pests into another territory with different vine species. Thus, phylloxera and the two common forms of mildew were native to North America, but became serious threats when they were introduced into Europe. The European grape vine, V. vinifera, has no natural defence against these pests and so succumbed to them.
In turn, the solution to some of these pests has been to use the natural resistance of American species to combat the disease; for example, the use of American rootstocks with a European scion.
What is phylloxera and how can it be managed?
This aphid-like insect feeds on and lays eggs on the roots of grape vines. It weakens vine roots and causes swellings and cracks, which then lead to rot. The insects can spread through crawling and flying and are 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.
The symptoms of phylloxera infestation are:
- 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.
It was identified in Europe in 1863 and was accidentally introduced from the USA, probably on the roots of imported vines. Initially, phylloxera spread rapidly and destroyed two-thirds of the European vineyard in the late nineteenth century.
Management options
In the nineteenth century it was noted that vineyards on sandy soil were immune to phylloxera, but this offers no help on other sorts of soil.
- The use of American vine species proved to be the way ahead, especially V. berlandieri, V. riparia and V. rupestris, which offer most protection. These species form hard, corky layers that surround the eggs, sealing the wounds and preventing invasion by bacteria or fungi. However, planting these American vines led to different and undesirable aromas in the resulting wine. The solution was to graft European varieties onto rootstocks from American vines.
- However, it was soon discovered that grafting onto the rootstocks of single American varieties caused problems in the typically calcareous soils of Europe as these varieties have little lime tolerance. The vines suffered from chlorosis turning the leaves yellow, halting photosynthesis and reducing yields and quality. The solution was to create rootstock hybrids between the various American species in order to balance the level of protection to phylloxera and resistance to lime in the soil.
- The use of rootstocks derived from American species enabled the development of many rootstocks, often with complex parentage, that can deal with a number of problems – phylloxera, nematodes, extremes of soil pH, water stress, salinity – and control the vigour of the vine.
- Today, the grape grower gets professional advice on the choice of rootstock and grape variety in order to match the appropriate rootstock to the vineyard soil, the pests to be combatted and the level of vigour desired (see Rootstocks in Planting Materials).
Planting on rootstocks is significantly more expensive than on the vines own roots, but has become a standard part of the cost of establishing a vineyard.
What are nematodes and how can they be managed?
Nematodes, tiny worms, are very common in soils, but are usually too small to be seen by the naked eye. Some cause damage by feeding off vine roots, significantly reducing yields and vigour. They can cause slow, gradual decline. Others transmit viral diseases. For example, fanleaf virus is spread by the dagger nematode.
Two of the most commonly occurring are root-knot nematode and dagger nematode. Nematodes are either present in the soil already or can be spread by unclean nursery stock, irrigation water or vehicles. Once present, they can only be managed, not eliminated.
Management options
Soil samples are taken and analysed in a laboratory to determine the number and type of nematodes present. Various options are available to the grower to combat nematodes:
- Leave the soil fallow for a number of years, but this is very expensive as no crop is produced.
- Fumigate the soil. Chemicals used to be used, but these are now banned in most regions. Another method is to plough in a cover crop of mustard plant, which contains compounds that work as biofumigants, killing nematodes.
- For most, the best solution is the use of nematode-resistant rootstocks.
What are grape moths and how can they be managed?
A number of different moths do damage to vines by feeding on flowers and grapes. Many species have several generations per season, attacking flowers in spring and grapes later in the year. The wounds created are then vulnerable to further attack from bacteria and fungi, including botrytis, and significant crop losses have been reported. The most common types are the light brown apple moth in Australia, the European grapevine moth in southern Europe and the grape berry moth in central and eastern North America. A number of species have inadvertently been imported into wine-growing areas even in recent times (e.g. European grapevine moth in the Napa Valley in 2009, declared eradicated in 2016).
Management options
Grape moths can be controlled by a number of measures:
- Biological controls include the use of:
the bacterium Bacillus thuringiensis (which produces substances that are toxic to the moths)
use of pheromone capsules to disrupt mating (‘sexual confusion’)
natural predators (parasitic wasps, green lacewings, some spider species). - Insecticides can be used.
What are spider mites and how can they be managed?
Several types of mites can damage vines, but spider mites are the most detrimental. The species of spider mite differs from region to region. Pacific spider mite is most destructive in California, while in Europe the red spider mite and two forms of yellow spider mite can cause damage. They feed on the surface cells of leaves. This leads to discoloration of the leaves, a reduction in photosynthesis, delayed ripening and a reduction in yields. Spider mites thrive in dusty conditions and are most damaging when vines are already water stressed.
Management options
A number of options can be considered:
- Make the environment inhospitable by the use of water sprinklers and/or cover crops or mulches to reduce dust.
- Encourage predatory mites (by planting host species) that feed on spider mites.
- General pesticides may kill beneficial predatory mites. Specific sprays can be applied to kill only the mites that are problematic in the vineyard, but this can add to costs.
Other insect pests include leafhoppers (they cause direct damage to vine leaves) and ladybirds (which can cause taints to the wine if they are in amongst harvested grapes).
What are birds and how can they be managed?
In nature, vines rely on birds to spread their seeds. However, birds can be a serious threat to vine growers as they destroy an entire crop of grapes as they ripen. Isolated vineyards that provide the only source of food in an area are particularly in danger. In addition to physical damage to grapes, bird damage allows bacteria and fungi to enter bunches, which leads to rot. Starlings are one species that often attack vineyards.
Management options
- The cost of total netting can be justified in high value areas (for example, Mornington Peninsula in Australia) or where birds are a major threat.
- Other measures such as bird scarers or noises can be used, but must be rotated regularly to avoid the birds getting used to them. Falcons are sometimes used to deter unwanted bird visitors.
