The Growing Environment Flashcards
At what temperature does vine dormancy occur? Winter freeze?
Temperatures under 10 degrees C ensure dormancy. Extreme temperatures of -20 or lower degrees C can cause winter freeze and damage the vine.
Above what temperature is bud burst stimulated and what helps this occur with more success and uniformity?
Temperatures above 10°C (50°F) stimulate budburst, and budburst is often more successful and uniform if there is a significant rise in temperature at this point. Warm soil temperatures can also promote budburst. Cold temperatures that bring frost can be very harmful for buds and new growth and can reduce yields substantially.
As the new shoots grow and leaves develop, the vine begins to what? What is the optimum temperature range for this?
Use photosynthesis to create sugar for energy. The optimum temperature range for this is approximately 18–33°C (64–91°F), and hence temperature is not usually a limiting factor at this time.
What are optimum temperatures for successful, uniform flowering? as well as fruit set?
Warm temperatures promote successful, uniform flowering (optimum above 17°C / 63°F) and fruit set (optimum range 26–32°C / 79–90°F), whereas cold, damp conditions can cause problems for flowering and fruit set and therefore reductions in yield and potentially quality of the grapes and wine.
What influence does temperature have on grape ripening?
Sugar accumulation in the grapes is generally faster at warm temperatures due to both optimum rates of photosynthesis producing sugars and because increased grape transpiration promotes the movement of sugar into the grape. Malic acid degradation is also increased at warm temperatures. Mean temperatures above 21°C (70°F) in the final month of ripening can lead to rapid loss of acidity, whereas mean temperatures below 15°C (59°F) can reduce acid loss to a point that acidity levels in the must are too high. The effect of temperature on the formation of aroma precursors and aroma compounds is very complex; generally riper aroma/flavours are associated with grapes grown in warmer climates. Cool conditions may hinder the breakdown of methoxypyrazines, which can give herbaceous aromas. In black grapes, anthocyanin synthesis (and therefore the development of colour) is optimum at 15–25°C (59–77°F).
What happens when extreme heat is paired with dry conditions?
Can cause photosynthesis to slow or stop, slowing vine growth and grape ripening. This is due to the heat sensitivity of enzymes that catalyse photosynthesis. In addition, water stress, which is typical in many hot regions, can also cause photosynthesis to slow down or stop due to the shutting of stomata to prevent water loss (see The Effects of Water). The closed stomata limit intake of carbon dioxide, which is needed for photosynthesis.
How does latitude effect sunlight?
If all other factors were equal, temperatures would be warmer and sunshine more intense in regions at lower latitudes than those at higher latitudes. Very broadly speaking, this means that grapes grown at lower latitudes can have higher levels of sugar, lower levels of acidity, riper aromas and, in black grapes, higher but riper tannins and more colour intensity than those at higher latitudes. Low latitude regions receive similar daylight hours (and hence heat and sunlight) throughout all seasons of the year. High latitude regions have longer daylight hours in the summer and shorter daylight hours in the winter. This permits a longer duration of time over which photosynthesis can take place in the growing season. Given the cooler temperatures in these locations, this can be useful in helping the vine to produce enough sugar for ripening grapes.
How can altitude offset lattitude?
Temperature falls by approximately 0.6°C (1.1°F) over every 100 m increase in altitude. High-altitude sites can therefore be favourable in areas of low latitude that would otherwise be too hot. By comparison, many of the best vineyard sites in high latitude areas, such as Burgundy and Loire Valley, are at relatively low altitudes, as otherwise temperatures would be too low for sufficient ripening
How does altitude affect diurnal range?
High-altitude sites often have a high diurnal range (the difference between day and night temperatures). The ground absorbs energy from solar radiation during the day and releases energy into the atmosphere during the night. At lower altitudes the air in the atmosphere (particularly the water vapour) absorbs some of this energy, meaning some heat is retained at night. At high altitudes the air is thinner and holds less moisture and therefore heat rapidly escapes, leading to relatively cool night-time temperatures. In warm climates, high diurnal range can be beneficial for the retention of acidity during grape ripening.
How does aspect impact ripening in high latitude sites?
The importance of aspect and the steepness of the slope increases at high latitudes. This is because solar radiation hits the Earth at a low angle at high latitudes. The slope increases the angle (nearer to perpendicular) at which the solar radiation hits the Earth’s surface, hence increasing the intensity of heat and light. The amount of warmth is also often a limiting factor in high latitude areas, so a slope can make a marked difference on the viability of a vineyard, what grape varieties can be grown there and the ripeness of those grapes.
How does aspect impact ripening in low latitude sites?
In warm climates, it may be desirable to limit the amount of heat and light. Planting on slopes that face away from the sun throughout most of the day can help achieve this. This may allow the grape grower to grow earlier-ripening grape varieties or produce wines with less alcohol and more acidity than would otherwise be the case at that latitude. For example, in Stellenbosch, white grape varieties are sometimes planted on south-facing slopes so that the grapes retain refreshing acidity.
What are the differences between east facing and west facing slopes?
Slopes facing east benefit from morning sunshine that can heat up the atmosphere when air and soil temperatures are at their lowest. This can extend the hours of vine growth and grape ripening each day, especially in cool climates. The grape canopy, which can be covered with dew in the morning, also dries out earlier in east-facing vineyards, reducing the spread of fungal disease, which is beneficial for grape quality and yields. Slopes that face west receive the afternoon sun and may become too hot, especially in warm climates, and risk of sunburnt grapes is increased (see Sunburn in Hazards). However, in areas with coasts to the west, e.g. California and Western Australia, cool afternoon sea breezes may alleviate this.
What are advantages and disadvantages to planting on slopes?
Slopes can provide additional benefits, including shallower, poorer soils and better drainage. Slopes can also provide shelter from winds and rain, and protection from frosts (air movement down the slope prevents frosts from forming; see Frosts in Hazards). However, soil erosion and inability to use machinery on steep slopes can be problematic.
Explain how proximity to water can have a significant impact on nearby vineyards?
This is because water heats up and cools down more slowly than dry land. During the day, the water and the air above a body of water remains relatively cool, and lowers the average temperature in the local area. Air directly above dry land heats up more quickly than that above the water, and this warm air rises. Cool air from above the water is drawn to the land to replace the warm air as it rises, resulting in cool, humid afternoon breezes.
The opposite happens at night. The water retains the warmth gained during the day, whereas, without solar radiation, the land loses heat relatively quickly. The warmth of the body of water keeps the local area warmer. The same effect can be experienced over the year, with large bodies of water giving cooler summers and milder winters.
Explain how proximity to water can be positive for both warm and cool climate regions?
Example of cool climate, in the Finger Lakes in New York, close proximity to the lakes reduces the severity of winter freeze, which would damage or even kill the vines. The movement of air also helps to protect against spring frosts that could reduce yields. By comparison, in Carneros, California, the proximity to the San Pablo Bay means that early-ripening grape varieties Chardonnay and Pinot Noir can be grown here (for still and sparkling wine), benefitting from cooling breezes, whereas later-ripening grape varieties such as Cabernet Sauvignon need to be grown further inland where warm afternoons help ripen the grapes.
