Mildew
/ˈmɪlˌdu/
Definition
Mildew refers to certain fungal-like plant diseases that produce a visible coating on leaves, stems, buds, or flowers. In gardening, the term most often means powdery mildew, which looks white or gray and sits on the surface, or downy mildew, which causes yellowing with fuzzy growth mainly on leaf undersides. It describes the disease symptom and the organisms causing it, not a normal plant feature.
Effects on Plants
- Reduced photosynthesis: On leaves, mildew can block light and interfere with gas exchange, which lowers photosynthesis and gradually weakens growth.
- Distorted new growth: Infected shoots, buds, and young leaves may curl, twist, or stay small, because tender tissues are more easily damaged as they expand.
- Favored by still, humid conditions: Crowded plants, poor air movement, and damp air often help mildew spread, even when foliage is not heavily wet.
- Common on susceptible ornamentals and crops: Roses, cucurbits, grapes, zinnias, and lilacs are frequent hosts, so recurring problems can point to plant choice as well as site conditions.
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