Which fungus is responsible for Powdery Mildew on grapes?

The fungus responsible for Powdery Mildew on grapes is Erisiphe necator. This organism is a fungal pathogen that specifically targets grapevines, leading to the characteristic white, powdery growth that can be observed on the leaves and fruit of the affected plants. The presence of this fungus can significantly impact grape quality and yield if not managed properly, making early detection and intervention crucial for grape growers.

Fundamentally, the other options listed do not cause Powdery Mildew on grapes. For instance, Planococcus citri refers to a type of mealybug, which is more of a pest issue than a fungal disease. Similarly, Pythopthora spp. are water molds known to cause root rot and other diseases in multiple plant species but are not associated with Powdery Mildew. Pseudococcus comstocki is another mealybug species and is likewise unrelated to the fungal infection identified in this question. Understanding the specific pathogens and pests affecting plants is vital for effective disease management and cultivation practices.