Grape downy mildew (Plasmopara viticola ) is one of the most common diseases in vineyards. It is also one of the most devastating, as it affects yields, wine quality and causes significant economic losses. Let’s find out more about this disease and what preventive solutions and biological treatments can be applied to combat this mildew.
How to prevent downy mildew in grapevines?
Prevention of grapevine mildew is based on several cultural practices which aim to minimize the conditions favorable to the development of the disease.
- Soil decompaction and aeration (using the biological solutions Siliboost and Silipellet ) is essential to avoid the accumulation of puddles of water around the vines.
- Act on humidity by causing the stagnant water on young organs to dry out (thanks to the natural product Bentobio )
- Trellising keeps the branches away from the ground. It thus reduces the risk of contamination by stagnant water .
- Leaf removal , which involves removing certain leaves around the clusters, promotes better aeration of the berries and reduces humidity, creating an environment less conducive to the development of mildew.
- It is recommended to avoid watering the foliage. Prefer watering at the foot of the vine , preferably in the morning, to reduce nighttime humidity which promotes spore germination.
- Regular spraying of biostimulants ( Yakapro ), Chitoprotect chitosane, horsetail decoction , willow bark infusion every one to two weeks from spring to autumn, strengthens the vine’s natural defenses against mildew.
- Planting density must also be controlled: avoiding planting vines too close together allows better air circulation and reduces conditions favorable to disease.
- Purchasing vine species that are less susceptible to mildew is an effective preventive strategy.
What biological treatments are there against Grape downy mildew?
Here are the organic treatments that we recommend against vine mildew.
For the decompaction and aeration of vineyard soils
For mildew treatments
Biostimulants
Fertilizers
Contact us for any additional information regarding our vineyard protocol.
Description of grapevine mildew
Downy mildew is a fungal disease caused by Plasmopara viticola . Originally from North America, downy mildew is now very common in France, where it was first observed in the late 19th century (1879) in the Bordeaux vineyards.
The impact of mildew on vines is devastating because it affects both the yield and the quality of the wines produced. Every year, it causes significant economic losses.
In viticulture , many grape varieties are sensitive to mildew, in particular
- Chardonnay
- Cabernet Franc
- Cabernet Sauvignon
- Pinot Noir
- Pinot Gris
- Merlot
- Sauvignon
- Riesling
- Grenache.
What are the conditions favorable to the development of grapevine mildew?
The parameters that encourage the development of Grape downy mildeware:
- warm climate (mild temperatures in spring)
- humidity (rainy spring)
- heavy dew
These conditions favor the germination of spores and the spread of the disease.
Biology of grapevine mildew
In winter, the fungus Plasmopara viticola survives in the form of oospores on fallen leaves. These oospores are resistant to low temperatures, they can withstand conditions below -20 °C, and their survival depends mainly on the humidity level and the amount of winter rain.
In spring , usually from April, the conditions become favorable for the germination of oospores. When the temperature reaches about 11°C and a minimum rainfall of 5 mm on the ground, the conditions are sufficient for their development, they begin to germinate in water. This process releases zoospores, responsible for the first contaminations of the vine tissues (primary contaminations).
Once the zoospores are released, they infect the vine tissues and the fungus enters the incubation phase. This incubation period can last from 7 to 14 days, depending on temperature and humidity conditions. During this phase, the mildew develops and prepares to produce new spores that will continue to infect the vine.
What are the symptoms of grape downy mildew?
Vine mildew affects all organs of the plant.
On the leaves
The first signs of mildew on leaves appear as oil spots . These are yellowish areas that appear on the upper side of the leaves. These affected areas can develop into necrosis (browning) and dry out.
In humid weather, a whitish down forms on the underside of the leaves.
These symptoms lead to a decrease in effective leaf area and a decrease in the photosynthetic activity of the plant.
At the end of the growing cycle, on older leaves, small yellow to brown spots, known as “mosaic” facies, may appear.
On the green branches (vine shoots)
Young branches have longitudinal superficial lesions that can lead to branch deformation. This condition makes the wood less suitable for hardening, making pruning more difficult and the passage of winter more difficult for the plant.
On the clusters
Before flowering, mildew can cause flower buds to dry out , which can lead to total loss of the crop.
On young bunches, the disease manifests itself by the formation of gray rot, a sort of whitish felting.
During later attacks, we observe clusters that turn a reddish-brown to purplish color (brown rot) and dry out.
After veraison, the grape clusters are no longer sensitive to mildew.
Other vine problems :
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