3.3 Managing Hazards, Pests, and Diseases

Even a perfectly trained vineyard can lose a crop to weather or biology. Level 3 expects you to name hazards, explain why they damage vines or fruit, and match practical countermeasures. Separate climatic hazards from pests and diseases, and always link the fix to the mechanism.

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Climatic Hazards and Responses

Spring Frost

Frost in spring kills tender green shoots and flowers when temperatures drop below freezing after budburst. Low-lying vineyards and frost pockets are highest risk because cold air drains downhill.

Common protections:

• Site selection — mid-slope sites with good air drainage; avoid hollows where cold pools.
• Heaters / smudge pots — warm a shallow layer of air (fuel cost and environmental drawbacks).
• Wind machines (fans) — mix warmer air from an inversion layer down into the vineyard when an inversion exists.
• Sprinklers — continuous water application forms ice that releases latent heat, keeping bud tissue near 0 °C if the system runs correctly throughout the event.

Delayed pruning can also postpone budburst slightly in some climates, reducing frost exposure windows.

Winter Freeze

Severe winter freeze can kill buds or, in extreme cold, damage trunks — especially grafted vines if the graft union is exposed. In very cold regions, growers may earth up (hill up soil) over the graft union for insulation, then remove soil in spring. Variety and clone hardiness also matter (hence hybrids in some cold climates).

Rain

Rain during flowering can impair fruit set; rain near harvest can swell and dilute berries, split skins, and promote grey rot. Responses include canopy openness for faster drying, careful spray programmes where allowed, drainage, and sometimes earlier harvest when rot risk outweighs further ripening.

Hail

Hail shreds leaves and damages berries, inviting infection and yield loss. Hail nets are an increasingly common physical defence in high-risk regions; insurance and site choice are other tools. Dense canopies do not reliably stop hailstones.

Water Stress and Irrigation

Water stress can be beneficial in moderation (limiting vegetative growth, concentrating fruit) but severe drought shuts down photosynthesis and ripening. Where irrigation is legal and available, growers choose delivery method carefully:

Exam focus: irrigation is a tool to manage stress, not automatically a quality negative or positive — timing and amount matter relative to climate and wine style goals. Dry farming (no irrigation) relies on winter rainfall storage and deep roots.

Sunburn

Sunburn browns and damages berry skins when sudden exposure (after aggressive leaf removal or heatwaves) coincides with intense radiation. Prevention: gradual leaf removal, retaining some west-side shade in hot sites, and avoiding abrupt canopy stripping before heat spikes.

Nutrient Deficiency

Vines need balanced nutrients (nitrogen, potassium, magnesium, iron, and others). Deficiencies show as chlorosis, poor shoot growth, or ripening problems. Causes include depleted soils, wrong pH locking up nutrients, or waterlogging. Fixes involve soil analysis, targeted fertilisation (within the chosen farming approach), cover crops, and drainage — not guesswork spraying alone.

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Pests

Phylloxera and Rootstocks

Phylloxera is an aphid-like insect that feeds on V. vinifera roots and devastated European vineyards in the 19th century. The enduring solution is grafting vinifera scions onto phylloxera-resistant rootstocks derived mainly from American Vitis species. Rootstocks also modulate vigour and tolerance to lime, drought, or nematodes. Own-rooted vinifera survives only in certain sandy soils or isolated phylloxera-free contexts.

Animals

Birds eat ripening fruit; deer, wild boar, and rabbits browse shoots or bunches. Controls include netting, fencing, falconry/scare devices, and habitat management. Animals are a physical problem — chemistry rarely replaces exclusion in premium fruit.

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Diseases

Fungal Diseases

Fungi thrive when humidity, warmth, and susceptible tissue coincide. Key exam families:

Canopy management is the cultural foundation; organic/biodynamic estates lean harder on copper/sulphur limits and prevention because many synthetic options are banned.

Viruses and Bacteria

Viruses (for example leafroll-associated viruses) are systemic: they reduce yield, delay ripening, and alter colour/sugar accumulation. They are spread by infected planting material and some insect vectors. Control is primarily certified virus-tested nursery stock, rogueing infected vines, and vector management — not a simple contact fungicide. There is no spray cure once a vine is infected, so the WSET answer is replacing the vine and sanitising the land: grub up the affected vines, clear root fragments, treat or rest the soil to remove the virus reservoir and its vectors, then replant with clean material. That sequence costs several vintages of production from the replanted block, which is why virus is a price and quality issue and not only a vineyard-health one.

Bacterial diseases (for example Pierce’s disease in some regions, or crown gall) likewise need region-specific vectors and sanitation strategies. For Level 3, remember the category difference: fungi often managed with sprays + canopy; viruses managed via plant material and removal.

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Integrated Thinking for SAQs

A strong answer names the hazard, the damage pathway, and two realistic controls. Example: spring frost → kill green shoots → wind machine if inversion + site selection. Example: phylloxera → root feeding on vinifera → resistant rootstocks. Avoid vague “spray everything” answers when the threat is viral or the estate is organic.

Key Takeaways

• Match frost tools to mechanism (heat, mixing, ice latent heat, site).
• Rain/hail/drought/sunburn each have distinct cultural or physical responses.
• Phylloxera → rootstocks; fungi → humidity + sprays/canopy; viruses → clean stock.