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| Downy Mildew |
Downy mildew is a major disease of grapevines caused by the fungal-like oomycete Plasmopara viticola. This species is unique to grapevines and is established in all Australian grape growing districts. It is spread by wind and water and favourable conditions for infection and disease development occur in warm wet weather, especially in late spring and early summer. In most districts, vines are at greatest risk from 3–6 weeks after budburst until berries are pea-sized. Inadequate control of downy mildew can result in severe crop losses. Most commercial varieties are susceptible to this disease. Essential components for strategic management of downy mildew include prediction of infection based on weather events, monitoring the vineyard for symptoms of infection, knowing the disease cycle, and understanding how cultural management practices and registered agrochemicals affect disease control. This page provides links to help growers understand and manage this grapevine disease.
Understanding Downy Mildew:
Downy mildew,
scientifically known as Peronospora and Plasmopara, is a group of pathogens
that primarily affect plants. Although they resemble fungi, downy mildews are
classified as oomycetes, which are more closely related to brown algae and
diatoms. These insidious microorganisms thrive in cool, moist conditions,
making them particularly problematic in regions with high humidity or during
wet seasons.
Symptoms of Downy Mildew:
Look for symptoms of downy mildew after suitable warm wet nights particularly in late spring and early summer.
- Yellow oilspots, initially with a chocolate-coloured edging, appear on upper leaf surfaces. On young leaves, oilspots can expand to around 50 mm diameter. ‘mosaic-like’ appearance of small angular yellow-brown spots confined by the leaf veins.
- Oily brown patches spread along infected shoots, stems and tendrils.
- Flowers, berries and whole bunches turn brown and have an oily appearance.
- Younger berries harden and turn
purplish if diseased, then brown before shrivelling and falling.
Symptoms of Downy Mildew on Grape berry 
Symptoms of Downy Mildew on Grape Leaf
Different types of Downy Mildew:
1. Downy Mildew of Grapes:
Downy mildew
(Plasmopara viticola), a fatal fungus that damages grapevines, is a frequent
problem for vineyards and grape farmers. The disease damages the leaves,
branches, and fruit, lowering the quality and quantity of the grapes. The
growth of oily-looking patches on the leaves, which eventually turn dark and
necrotic, is one sign of the disease. The use of disease-resistant grape types,
regular pruning to increase air circulation, and the use of copper-based
fungicides are just a few of the tactics grape growers use to battle this
threat.
2. Downy Mildew of Maize:
Corn crops are seriously threatened by the pathogen Peronosclerospora spp.'s downy mildew of maize. The characteristic symptoms of this illness, which can swiftly spread throughout the plant, are white or greyish patches on the leaves. The plant's capacity to photosynthesize is hampered as it progresses, resulting in lower yields and limited growth. Farmers frequently employ fungicides and resistant cultivars of maize to battle downy mildew. In addition to crop rotation, effective field sanitation is essential for managing disease.
3.Downy Mildew of Cucurbits:
Prevention and Control:
Preventing and controlling downy mildew in crops is essential to ensure healthy yields and economic viability. Here are some general tips and strategies for managing downy mildew:
1.Weather Monitoring:
- It's crucial to keep an eye on the weather when deciding whether or not to use sprays. In some areas, downy mildew infection advisories are issued based on Bureau of Meteorology warnings. Sprays intended to prevent infection should be used as soon as feasible before an infection occurs.
2. Viticulture Practice:
- Practises that promote air movement, sunlight penetration, and spray penetration into the canopy can lessen the likelihood of infection and the subsequent onset of disease.
- Utilising the prevailing breeze that moves along rows will help leaves dry out more quickly.
- Avoiding crowding and promoting open canopies through planting densities, trellising, and training techniques.
- The vine framework is made more accessible by canopy management techniques like leaf picking, shoot thinning, hedging, and skirting.
3.Chemical Strategies:
There are two strategies for
chemical control of downy mildew based on whether sprays are applied pre- or
post-infection.
- The pre-infection technique entails applying a 'protectant' fungicide with enough coverage before climatic conditions that favour disease growth. The chemical functions as a barrier, preventing spores from reaching the vine tissue.
- In accordance with the post-infection strategy, an 'eradicant' fungicide must be sprayed right away after an infection event has taken place. If the necessary chemicals are applied within five days of the circumstances that made an infection more likely and before oil marks form, more spraying shouldn't be required until the circumstances that made an infection more likely to occur again.
Keep in mind that
grapes are more than just a crop; they are a representation of history, culture,
and delectable flavours. For many people, protecting their health and vitality
is more than just a duty. You may protect the future of your vineyard and the
calibre of your wine by putting into practise the best practises covered in
this blog, from good pruning and canopy management to the prudent use of
fungicides and the adoption of disease-resistant grape varietals.
Raise a glass in
support of healthy, disease-free grapevines and the ongoing development of this
traditional custom. A prosperous and abundant harvest is toast!
To read about more grape diseases/ deficiencies Click Here!
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