Powdery mildew is a grapevine disease caused by the fungus Erysiphe necator, also known as Uncinula necator. It can infect leaves, shoots, flowers and berries, producing a white or grey powdery growth. Severe infections can reduce photosynthesis, damage berries, cause splitting and increase the risk of secondary rot.
Powdery mildew may appear as pale patches on leaves that develop into a white-grey powdery coating. Infected berries can become covered with fungal growth, stop developing normally or split as the skin loses elasticity. Infection of flower clusters can reduce fruit set and crop yield. Symptoms can be mistaken for dust or other surface deposits, so vineyard monitoring is important.
Unlike downy mildew, powdery mildew does not require free water on the plant surface to infect. Moderate temperatures, humid conditions and dense canopies can favour disease development. The fungus overwinters in vineyard material and can spread through airborne spores during the growing season.
Management includes canopy opening, shoot positioning, disease monitoring and permitted fungicide applications. Sulphur is widely used in many wine regions and organic systems, subject to temperature, timing and local rules. Excessive heat during sulphur application can cause phytotoxicity, so label directions and regional guidance must be followed.
Example: a vineyard may apply a permitted sulphur treatment during the growing season to reduce powdery mildew pressure, while maintaining an open canopy for airflow and spray coverage.
Powdery mildew is a true fungal disease and can infect without free water on the leaf surface. Downy mildew is caused by an oomycete and is strongly associated with wet conditions. Both can cause significant crop losses if not managed.
Chef’s note: powdery mildew affects grapes in the vineyard and is not the same as the natural bloom on healthy grapes or a wine fault.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
