Powdery mildew of grape, a widespread fungal disease, is a constant threat to vineyards around the world. This fungus not only compromises the health of the vines, but also the quality and yield of the harvests. But how can you identify its damage and intervene in time to limit its spread? Find out everything you need to know about this disease and find our solutions and control protocols.
What is grape powdery mildew of grape?
Powdery mildew of grapevines, caused by the fungus Erysiphe necator ( Uncinula necator ), is a fungal disease that exclusively affects grapevines. This parasite, unable to survive outside of this plant, attacks its various parts, compromising its development and productivity.
Originally from North America, powdery mildew was introduced to France in 1847, in the Paris region, before reaching Bordeaux in 1852. Since then, it has spread to all French and global vineyards, becoming a constant threat to crops.
Although its first infections are invisible to the naked eye, they develop quickly, making them complex to control. Powdery mildew is now one of the most important diseases of the vine.
What are the factors that favor development?
The development of powdery mildew of grape depends strongly on environmental conditions:
- Temperatures between 20 and 25°C provide optimal conditions for the growth of the fungus.
- High humidity : a high humidity level, combined with low light, encourages its development.
- Wind dispersal : Powdery mildew spores are carried by the wind, facilitating their spread over wide areas.
What are the symptoms of powdery mildew of grape ?
Powdery mildew of the vine is observed on different organs of the plant:
On young shoots
The first attacks of powdery mildew appear on young shoots by a slowdown in their growth. On sensitive grape varieties, a whitish down appears, a sign of active colonization of the fungus. These symptoms affect the vitality of the plants from their initial development.
On the leaves
Affected leaves have oily spots that develop into a powdery texture , particularly visible on the upper surface. The veins underneath turn black. The leaf blade becomes deformed and the edges become curled.
On the clusters
On berries, powdery mildew forms a thin gray layer resembling ash. This powder, consisting of mycelium and conidia, leads to the death of surface cells, causing the fruits to burst. This mechanical damage exposes the berries to other infections, and a moldy smell is released from diseased bunches, harming their quality and marketability.
On the vine shoots
The vine shoots are not spared. Before they turn brown, brown spots appear, later evolving into a reddish tint. In the fall, cleistothecia form in the form of dark blisters, marking the winter persistence of the fungus.
What is the impact of powdery mildew on vineyards?
The consequences of powdery mildew in viticulture result in significant losses for winegrowers. Yield reduction is one of the first effects observed, with affected berries unable to reach full maturity. The quality of the fruit deteriorates, which directly affects the quality of the wines produced.
Berry bursts promote the entry of secondary pathogens such as Botrytis, which increases infections and losses. The deterioration of the bunches thus compromises the entire production chain, from harvest to bottling, impacting the profitability of the farms.
Development and biology of powdery mildew of grape
Powdery mildew on grapevines adopts different strategies to get through the winter periods and redeploy in the spring. In the form of mycelium , it settles in dormant buds, where it survives until the vegetative recovery. During this phase, it causes stunted shoots accompanied by curled leaves, often called “flag symptoms”. Another form of conservation is based on cleistothecia , small spherical structures nestled in the bark of the vines. The latter release ascospores in the spring, favored by the action of rain.
The biological cycle of the fungus occurs in two stages. Primary contamination begins with the emergence of ascospores and the activation of the overwintering mycelium, affecting the young tissues of the vine. Then, secondary propagation comes into play, thanks to conidia carried by the wind. These spores quickly find receptive areas, such as leaves or grape clusters, where they germinate, triggering a new phase of infection. This mechanism makes powdery mildew particularly aggressive in favorable conditions.
Fight against powdery mildew of grape
Powdery mildew management is based on a combination of appropriate cultural practices and increased monitoring. Hot and humid periods are windows of opportunity for the fungus to spread. Particular vigilance is necessary during these phases to detect the first signs of contamination.
Vineyard aeration plays a key role in prevention. By reducing planting density and carrying out interventions such as leaf removal or disbudding, it is possible to limit humidity between plants.
Agrobiotop solutions:
At Agrobiotop, we manufacture natural solutions to strengthen plants and combat diseases such as vine powdery mildew of grape:
- CHITOPROTECT (chitosan) basic substance
- YAKAPRO (biostimulant)
- BENTOBIO : to dilute 1 to 2 kg / 100 liters of water / hectare or as a powder at a dose of 8 to 15 kg / hectare
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