Powdery mildew diseases infects many plant species. It common on roses, lilacs, English oak, sycamore, some deciduous azaleas and zinnias. Usually when powdery mildew infects one type of plant, it does not infect any other type. Each plant type is unique in that the powdery mildew that infects it will not infect any other.
Powdery mildew is caused by
A) a virus.
B) a fungus.
C) genetics.
D) a bacteria.