Hazards, Pests and Diseases Flashcards
Drought - The importance of water
Vines need water to grow and produce high quality fruit at yields that make grape growing financially viable. 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 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.
Drought managment
Where 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 planted, drought resistance should be high on the list of priorities in choosing a rootstock. Ex V rpestris, V berlandeieri parentage
Choose a drough tolerant variety such as Garnacha
Excess of water
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
Managment of excess of water
If there is excess rainfall on a regular basis, then 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.
Rainfall
Rainfall during pollination and fruit set can lead to millerandage or coloure, reducing the size of the crop and potentially also lowering quality. Rain during summer can also reduce the rate of ripening of fruit. Mild water deficiency before veraison 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)
managing rainfall
Choice of site (slope, climate), condition of the soil, choice of whether or not to grass the land between the rows of vines and the adequacy of drainage can mitigate some effects of untimely rainfall.
Monitoring weather forecast: in the case of forecast of heavy/prolonged rain, winemakers may have to weight 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 the crop.
Freeze
Fully dormant vines are relatively hardy and can tolerate quite severe frost. However, if temperatures fall below -20, the vine can be seriously damaged or eve killed by winter freeze. If vines are grafted onto rootstock, the graft is the part of the vine that is most at risk. The canes or cordons are the next at risk. Frost can kill canes or cordons or kill all parts of the vine above the ground, leading to the need to replace the vine. Areas more affected are Canada, Washington State and China
Freeze management options - Site selection
Hill sites can be up to 5C 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
Freeze management options
1.Site selection (hill sites)
2.Choice of varieties (Cabernet Franc, Riesling, American an Mongolian vine species)
3.Protecting vines ( building up soil around the vine, burying vines, pruned to have several trunks)
Types of frost
- Advective frost are caused by large volumes of cold air moving in from very cold areas
- Radiative frost 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.
Reducing risk of frost
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
Choosing a variety that buds late, such as Riesling
Vines trained high off the ground offer more protection
Having bare soil between the vines absorbs more heat during the day and radiates this heat during the night
Options when frost threatens
- Water sprinklers: also known as aspersion. If the vineyard already has an irrigation system, then sprinklers can be used. Alternatively, sprinklers can be installed specifically for frost protection. As water freezes around the parts of the plant, it releases latent heat, protecting the plant.
- Wind machines: large fans 4-7m high, pull warmer air from above down to ground level, thereby raising the temperature.
- Oil or propane gas burning heaters and wax candles 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
Hail
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 season. If the damage is caused early in the season, the vine may be able to reshoot from existing buds.
