Identification Symptoms

  • Powdery mildew, caused by the fungus Uncinulanecator, can infect all green tissues of the grapevine.
  • Tissues are generally susceptible to infection throughout the growing season.
  • Diseased leaves appear whitish gray, dusty, or have a powdery white appearance. Petioles, cluster stems, and green shoots often look distorted or stunted. Berries can be infected until their sugar content reaches about 8%.
  • If infected when young, the epidermis of the berry can split and the berries dry up or rot. When older berries are infected, a netlike pattern often develops on the surface of the berry.