There are many different species of the fungal disease powdery mildew, and each species attacks a range of different plants. Unlike many other fungal diseases, powdery mildew thrives in warm, dry climates, though it does require fairly high relative humidity (i.e., humidity around the plant) to spread. In cooler, rainy areas, it does not spread as well. That being said, it is capable of infecting your plants under a wide variety of conditions. When the fungus begins to take over one of your plants, the mildew that forms is made up of many spores. These spores carry the infection to other plants through the wind. Powdery mildew can slow down the growth of your plant. In some cases, if the infection is severe enough, powdery mildew can kill your plants. Powdery mildew, a group of fungal diseases that are prevalent in warm, wet weather, is one of the most common and easily recognized plant diseases. Almost no type of plant is immune, however, some are more susceptible than others. Lilacs, crab apples, phlox, monarda, roses, grapes, squash, and cucumbers are all likely targets for powdery mildew.