WSET Diploma D1 Exercises (Hazards, Pests and Diseases: part 1)

Answer

When water becomes scarce by drought, vines close the stomata on their leaves to reduce water loss. This limits photosynthesis, which in turn slows down vine growth, reduces berry size, and delays ripening. As a result, grapes may remain under-ripe, leading to lower yields and poor fruit quality. If drought persists for an extended period, vines may lose their leaves and eventually die.

To manage drought, grape growers can implement irrigation systems, provided they are permitted in the region. Establishing vineyards near reliable water sources or on soils with good water retention can also help mitigate water stress. Another effective strategy is choosing drought-tolerant grape varieties and rootstocks. For example, Garnacha is known for its high drought resistance, and rootstocks derived from V. rupestris and V. berlandieri (such as 110R and 140R) provide excellent drought tolerance.

Grading Criteria

• Impact
  • For pointing out that vines close the stomata on their leaves to reduce water loss until drought, you get 1 point.
  • For explaning that this limits photosynthesis, you get 1 point.
  • For explaining that this slows vine growth, reduces berry size, and delays ripening, you get 1 point each, for a total of 3 points.
  • For the conclusion that grapes may remain under-ripe, leading to lower yields and poor fruit quality, you get 1 point.
  • For pointing out that if drought persists for an extended period, vines may lose their leaves and eventually die, you get 1 point.
• How to manage
  • For pointing out that grape growers can implement irrigation systems to manage drought, you get 1 point.
  • For pointing out that producers establish vineyards near reliable water sources to manage drought, you get 1 point.
  • For pointing out that producers establish vineyards on soils with good water retention to mitigate water stress, you get 1 point.
  • For pointing out that producers choose drought-tolerant grape varieties and rootstocks to mitigate water stress, you get 1 point.
  • For providing an example of a drought-tolerant grape variety, such as Garnacha, you get 1 point.
  • For providing an example of a drought-tolerant rootstock, such as V. rupestris and V. berlandieri, you get 1 point.

Answer

Excess water promotes excessive vegetative growth, leading to competition for carbohydrates between shoots and fruit. This can result in under-ripe grapes, reduced yields, and lower fruit quality. Additionally, dense canopies block sunlight, further inhibiting grape ripening. High moisture levels also increase humidity, creating favorable conditions for fungal diseases, which can significantly reduce yields and damage fruit quality. If the soil is not well-drained, waterlogging can occur, reducing oxygen availability to the roots, slowing vine growth, and potentially causing vine death. Waterlogging can also compact the soil, making vineyard operations more difficult and restricting proper water flow.

To manage excess water, grape growers can plant vineyards on slopes or choose well-draining soils, such as sandy or gravel-based soils, to prevent water accumulation. Installing a drainage system can also help redirect excess water away from the vines.

Grading Criteria

• Impact
  • Vigor
    • For pointing out that excess water promotes excessive vegetative growth, you get 1 point.
    • For explaning that this leads to competition for carbohydrates between shoots and fruit, you get 1 point.
    • For the conclusion that this results in under-ripe grapes, reduced yields, and lower fruit quality, you get 1 point each, for a total of 3 point.
    • For pointing out that dense canopies block sunlight, further inhibiting grape ripening, you get 1 point.
  • Humidity
    • For pointing out that excess of water increase humidity, creating favorable conditions for fungal diseases, you get 1 point.
    • For explaining that this can significantly reduce yields and damage fruit quality, you get 1 point. A broader range of answers may be accepted if they effectively describe the impact of fungal diseases on grapes.
  • Water logging
    • For pointing out that if the soil is not well-drained, waterlogging can occur, you get 1 point.
    • For explaning that this reduce oxygen availability to the roots, you get 1 point.
    • For the conclusion that this slows vine growth, and potentially causes vine death, you get 1 point.
    • For the explaning that waterlogging can compact the soil, you get 1 point.
    • For the conclusion that this makes vineyard operations more difficult and restricting proper water flow, you get 1 point.
• How to manage
  • For identifying planting vineyards on slopes as an option for managing excess water, you get 1 point.
  • For identifying choosing well-draining soils as an option for managing excess water, you get 1 point.
  • For identifying installing a drainage system as an option for managing excess water, you get 1 point.
  • For explaining that these options prevent water accumulation, you get 1 point.

Answer

Untimely rainfall can negatively impact vines and wine production at various stages of growth. During flowering and fruit set, excessive rain can cause coulure (poor fruit set) and millerandage (uneven berry development), reducing both yield and fruit quality. During the ripening period, heavy rain can dilute the grape’s sugar and aromas, slowing down ripening and lowering wine quality. Excess water can also cause grape splitting, increasing the risk of fungal diseases such as botrytis (grey rot). Excess rainfall near harvest hinders operations by making vineyards difficult to access, preventing the use of mechanical harvesters and manual pickers, especially in clay soils.

Monitoring weather forecasts allows grape growers to make timely decisions, such as harvesting earlier to avoid rain. Additionally, proper site selection is crucial—planting vineyards on well-drained soils or slopes helps prevent water accumulation and reduces disease pressure.

Grading Criteria

• Impact
  • During flowering and fruit set
    • For pointing out that excessive rain during flowering and fruit set can cause coulure and millerandage, you get 1 point.
    • For explaning that this reduces both yield and fruit quality, you get 1 point.
  • During the ripening period
    • For pointing out that heavy rain during the ripening period can dilute the grape’s sugar and aromas, you get 1 point.
    • For explaning that this slows down ripening and lowers wine quality, you get 1 point.
    • For pointing out that excess water can cause grape splitting, you get 1 point.
    • For explaning that this increases the risk of fungal diseases, you get 1 point.
  • Near harvest
    • For pointing out that excess rainfall near harvest hinders operations by making vineyards difficult to access, you get 1 point.
    • For explaning that this prevents the use of mechanical harvesters and manual pickers, you get 1 point.
• How to manage
  • For identifying weather monitoring as a management strategy, you get 1 point
  • For explaning that this allows grape growers to make timely decisions, you get 1 point.
  • For providing an example of a timely decision, such as harvesting earlier to avoid rain, you get 1 point.
  • For identifying planting vineyards on well-drained soils or slopes as a management strategy, you get 1 point.
  • For explaning that this prevents water accumulation and reduces disease pressure, you get 1 point.

Answer

Winter freeze can cause severe damage to vines, potentially killing the entire plant if temperatures drop below -20°C. The graft union is the most vulnerable part, followed by the canes and cordons, which can also suffer significant damage. Severe freeze can greatly reduce yields or even necessitate complete vine replacement, leading to economic losses for growers.

To manage freeze, growers can bury the graft union under soil (‘hilling up’) or rely on snow coverage, which acts as insulation. Site selection is also crucial—planting on hillsides or near large bodies of water helps because these locations tend to be warmer than valley floors and prevent cold air from stagnating. Choosing cold-hardy varieties like Riesling and Cabernet Franc, as well as American vine species such as V. amurensis and their hybrids, can significantly improve freeze resistance. Additionally, pruning vines to have multiple trunks allows growers to replace damaged parts more easily and maintain productivity.

Grading Criteria

• Impact
  • For pointing out that winter freeze causes severe damage to vines and potentially killing the entire plant, you get 1 point.
  • For identifying the condition causing the previous impact, when temperatures drop below -20°C, you get 1 point.
  • For explaning that the graft union is the most vulnerable part, you get 1 point.
  • For the conclusion that this greatly reduce yields or even necessitate complete vine replacement, you get 1 point.
• How to manage
  • For pointing out that growers bury the graft union under soil or rely on snow coverage to manage winter freeze, you get 1 point.
  • For explaning that this acts as insulation, yot get 1 point.
  • For pointing out that grape grower plants on hillsides or near large bodies of water to manage winter freeze, you get 1 point.
  • For explaining the above reason, that these locations tend to be warmer than valley floors and prevent cold air from stagnating, you get 1 point.
  • For pointing out that choosing cold-hardy varieties is one of the management strategies, you get 1 point.
  • For listing an example of cold-hardy varieties, such as Riesling, Cabernet Franc, American vine species (e.g. V. amurensis) and their hybrids, you get 1 point.
  • For pointing out that pruning vines to have multiple trunks is one of the management strategies, you get 1 point.
  • For explaning that this allows growers to replace damaged parts more easily and maintain productivity, you get 1 point.

Answer

Spring frost occurs when temperatures drop below 0°C, damaging or even killing newly emerged buds and young shoots. If frost is widespread, yields can be significantly reduced. While vines can produce secondary buds, these are typically less fruitful and take longer to ripen, which can delay harvest and impact fruit quality.

Planting on slopes or near large bodies of water helps mitigate frost risk, as these locations tend to be warmer than valley floors and promote air movement, preventing cold air from settling. Delaying pruning can also postpone budburst until warmer months, reducing the risk of frost damage. High-trained vines offer more protection, as the coldest air stays closer to the ground, while maintaining bare soil between vine rows (rather than using cover crops) allows the soil to absorb and radiate more heat at night.

If frost occurs, several active measures can be taken. Sprinkler systems can be used to coat the vines with water, which releases latent heat as it freezes, protecting the buds. Wind machines help by mixing warmer air from higher layers with cold air near the ground, raising temperatures. Heaters or controlled fires placed strategically in the vineyard generate heat and enhance air circulation, preventing cold air from settling. Additionally, growers can choose late-budding grape varieties like Riesling, which are less likely to be affected by early spring frosts.

Grading Criteria

• Impact
  • For explaning that spring frost damages or even kills newly emerged buds and young shoots, you get 1 point.
  • For explaning that spring frost occurs when temperatures drop below 0°C, you get 1 point.
  • For explaning that this reduces yields significantly, you get 1 point.
  • For pointing out that although vines can produce secondary buds, these are typically less fruitful and take longer to ripen, you get 1 point
  • For explaning that this delays harvest and impacts fruit quality, you get 1 point.
• How to manage
  • Location
    • For identifying planting on slopes or near large bodies of water as a mitigating option of frost, you get 1 point.
    • For explaning that this locations tend to be warmer than valley floors, you get 1 point.
    • For explaning that this locations promote air movement, preventing cold air from settling, you get 1 point.
  • Delaying pruning
    • For identifying delaying pruning as a management option, you get 1 point.
    • For explaining that this delays budburst until warmer months with a lower risk of frost, you get 1 point.
  • High-trained
    • For identifying high-trained vines as a protecting option, you get 1 point.
    • For explaining the above reason, that the coldest air stays closer to the ground, you get 1 point.
  • Maintaining bare soil
    • For identifying maintaining bare soil between vine rows as protecting option, you get 1 point.
    • For explaning that this allows the soil to absorb and radiate more heat at night, you get 1 point.
  • Sprinkler systems
    • For identifying sprinkler systems as a management option, you get 1 point.
    • For explaining that sprinkled water releases latent heat as it freezes, protecting the buds, you get 1 point.
  • Wind machines
    • For identifying wind machines as a management option, you get 1 point.
    • For explaning that wind machines mixes warmer air from higher layers with cold air near the ground, you get 1 point.
  • Heater
    • For identifying heaters or controlled fires as a management option, you get 1 point.
    • For explaning that this generate heat and enhance air circulation, preventing cold air from settling, you get 1 point.
  • Choosing late-budding grape varieties
    • For identifying choosing late-budding grape varieties as a management option, you get 1 point.
    • For listing an example of late-budding grape varieties as Riesling, you get 1 point.
    • For explaning this is less likely to be affected by early spring frosts, you get 1 point.

Answer

Hailstones can tear or destroy young shoots and leaves, weakening its overall growth. Ripening grapes can be bruised or split, creating entry points for fungal diseases such as botrytis, further compromising fruit quality. In extreme cases, hail can lead to significant yield loss in both the current and following seasons.

To manage hail risk, growers often use protective netting to shield vines. Additionally, in some regions, rockets containing silver iodide (AgI) are launched into thunderclouds to encourage rainfall instead of hail formation.

Since hailstorms tend to be highly localized, growers in hail-prone regions may choose to spread their vineyards across multiple sites to ensure production continuity. Another option is crop insurance, which can help mitigate the financial impact of severe hail damage.

Grading Criteria

• Impact
  • For pointing out that hailstones tear or destroy young shoots and leaves, you get 1 point.
  • For explaning that this weakens vine’s overall growth, you get 1 point.
  • For pointing out that ripening grapes can be bruised or split by hailstones, you get 1 point.
  • For explaning that this creates entry points for fungal diseases, you get 1 point.
  • For coucluding that hail can lead to significant yield loss by above reason, you get 1 point.
  • For pointing out that this yield loss occurs in both the current and following seasons, you get 1 point.
• How to manage
  • For identifying using protective netting to shield vines as a management option, you get 1 point.
  • For identifying launching rockets containing silver iodide (AgI) into thunderclouds as a management option, you get 1 point.
  • For explaning that this encourages rainfall instead of hail formation, you get 1 point.
  • For identifying spreading vineyards across multiple sites as a management option, you get 1 point.
  • For explaning that this ensures production continuity, you get 1 point.
  • For identifying crop insurance as a management option, you get 1 point.
  • For explaning that this mitigates the financial impact of severe hail damage, you get 1 point.

Answer

Sunburn damages grape quality by causing scars, browning, bitterness, and increased susceptibility to rot. In severe cases, grapes may shrivel and die, leading to reduced yields.

To prevent sunburn, growers use canopy management by avoiding excessive leaf removal and positioning shoots and leaves to provide natural shade. Bush vines can also help by shielding grapes with their drooping shoots. Adjusting row orientation reduces exposure to intense afternoon sun, and additional irrigation during heatwaves can minimize water stress, which increases sunburn risk. Other strategies include applying agricultural sunscreen sprays and using shade cloths or netting.

Grading Criteria

• Impact
  • For explaining that sunburn causes scars, browning, bitterness, and increased susceptibility to rot, you get 1 point each, for a total of 4 points.
  • For pointing out that grapes may shrivel and die in severe cases, you get 1 point.
  • For explaning that this leads to reduced yields, you get 1 point.
• How to manage
  • For identifying canopy management as a management option, you get 1 point.
  • For listing an example of canopy management such as avoiding excessive leaf removal and positioning shoots and leaves to provide natural shade, you get 1 point.
  • For identifying bush vines as a management option, you get 1 point.
  • For explaning that bush vines shield grapes with their drooping shoots, you get 1 point.
  • For identifying adjusting row orientation as a management option, you get 1 point.
  • For explaning that this reduces exposure to intense afternoon sun, you get 1 point.
  • For identifying additional irrigation during heatwaves as a management option, you get 1 point.
  • For explaning that this minimize water stress which increases sunburn risk, you get 1 point.
  • For identifying agricultural sunscreen sprays and the use of shade cloths or netting as management options, you get 1 point each, for a total of 2 points.

Answer

Fire can directly damage vines, leading to lower yields, vineyard loss, and destruction of facilities and equipment. However, the most significant impact on wine quality comes from smoke taint.

Smoke taint occurs when grapes absorb aromatic compounds from smoke, which then bind with sugars to form non-aromatic precursors. These compounds release undesirable smoky, plastic-like aromas during fermentation and aging, negatively affecting wine quality.

There are limited ways to protect vineyards from fire, but growers can install sprinklers, maintain water tanks, and train employees for emergency response.

To mitigate smoke taint, winemakers can analyze musts before harvest using laboratory tests or micro-vinifications to assess the level of contamination. Additionally, handling grapes carefully—such as hand harvesting, gentle pressing, reducing maceration time, and fermenting at lower temperatures—can help minimize the extraction of smoke compounds. Further treatments, such as flash détente and reverse osmosis, may reduce smoke taint but cannot fully eliminate it. Blending affected wines with unaffected ones is another possible solution to improve balance and overall quality.

Grading Criteria

• Impact
  • Fire
    • For identifying lower yields, vineyard loss, and the destruction of facilities and equipment as impacts of fire, you get 1 point each, for a total of 3 points.
    • For explaining that fire causes smoke taint, you get 1 point.
  • Smoke taint
    • For explaning that smoke taint bind with sugars to form non-aromatic precursors, you get 1 point.
    • For explaning that these compounds release undesirable smoky, plastic-like aromas during fermentation and aging, you get 1 point.
• How to manage
  • Fire
    • For identifying installing sprinklers, maintaining water tanks, and training employees for emergency response as a mitigating strategy, you get 1 point each, for a total of 3 points.
  • Smoke taint
    • For identifying the use of laboratory tests and micro-vinifications to analyze musts before harvest as a strategy to assess contamination levels, you get 1 point each, for a total of 2 points.
    • For identifying that careful handling of grapes minimizes the extraction of smoke compounds, you get 1 point.
    • For listing examples of careful handling, such as hand harvesting, gentle pressing, reducing maceration time, and fermenting at lower temperatures, you get 1 point each, up to a maximum of 2 points.
    • For identifying flash détente and reverse osmosis as reducing strategy, you get 1 point.
    • For identifying blending affected wines with unaffected ones as a strategy to improve balance and overall quality, you get 1 point.