Linked from
The 6 pages that link to Powdery mildew, each with the reason it gives.
AscomycotaBroader topic: These plant diseases are caused by members of Ascomycota.
CucurbitaceaeRelated: It commonly damages cucurbit foliage and can reduce crop yield.
Summer squashRelated: It commonly reduces the vigor and productivity of squash foliage.
Vitis viniferaRelated: It can damage vinifera vines and reduce fruit quality.