The best way to prevent a powdery mildew problem is to only grow plants that have been bred to resist it. These plants are especially prone to mildew: A good rule of thumb, then, is to give plants as much sun as they can tolerate rather than too much shade. The same holds true for bee balms, which also tolerate shade but are apt to be healthier and more flowerful in full sun. As those bushy perennials usually have many stems all crowded together, powdery mildew spores travel quickly among their foliage. Garden phloxes, for example, frequently end up in less-than-sunny beds since they can tolerate and bloom under such conditions. Some plants are especially prone to powdery mildew, especially those set closely together in the shade. RELATED: How to Get Rid of Fungus Gnats: 4 Remedies That Work Vulnerable Plants Infected trees may lose some of their resilience and succumb to winter weather or “wake up” (leaf out) later than usual in spring. In vegetables, the shape and flavor of fruits may also be adversely affected. Powdery mildew symptoms can include discolored or distorted leaves and blooms and burnt or dead-looking tissue, which often prevents affected flowers from opening at all. In addition to the unsightly white powder on plants that it creates, this fungal disease sucks much of plants’ vitality from their foliage and flowers. After leaves drop in the fall, fungi can linger in their debris to infect more plants the following spring. If that initial “pox” isn’t noticed, the white spots might spread via wind or rain-borne spores to coat the entire plant and other nearby ones. Powdery mildew often makes its first appearance as tiny white spots on plant leaves. In some species, though, these diseases will manifest as red or yellow “burn” marks on leaves rather than a white coating. When in full “bloom,” mildews typically cause plants to look as if they’ve been dusted with gray or white powder. Powdery mildew is most likely to affect species that are overcrowded or aren’t receiving enough sunlight. Watch for white spots on leaves in spring or autumn when warm, dry days-with temperatures up to 80 degrees Fahrenheit-are followed by cool, humid nights that drop down to 60 degrees. Powdery mildew on leaves generally isn’t harmful to people-except those sensitive to molds and mildews, in whom it may cause allergy symptoms. However, Podosphaera xanthii, which affects a variety of cucurbits like cucumber and squash, also can spread to unrelated flowering plants like calibrachoas and petunias. The lilac powdery mildew ( Microsphaera syringae), for example, affects only lilacs, while rose mildew ( Podosphaera pannosa) also affects briars closely related to roses, such as blackberry and raspberry. Diseases caused by fungi whose spores spread from plant to plant via wind or rain, some types of powdery mildew are specific to certain fungal species and others to certain plant families, while still others are less picky. There are actually a variety of powdery mildews, not just one. RELATED: 10 Common Garden Problems-and How to Fix Them What Is Powdery Mildew? That means the best way to prevent powdery mildew is to keep your plants as healthy and happy as possible. Powdery mildew is most likely to affect species already weakened by poor care or conditions, especially plants that aren’t getting their fair share of sun or space.
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