In a plant environment, which disease can cause a white dusty layer on leaves such as Lilac, Crape Myrtle, chrysanthemums, asters, strawberries, rosemary, and roses?

• A. Botrytis
• B. White rust
• C. Powdery mildew
• D. White powdery smut

Answer: (C)

Powdery mildew is a fungal disease that creates a white, dusty coating on leaf surfaces. The fine white powdery spores form a visible film that can cover the upper (and sometimes lower) leaf, stems, and even flower buds. It tends to show up in conditions with warm days and cool, somewhat humid nights, especially when air movement is limited or plants are crowded. The result is a chalky white appearance as the disease feeds on the leaf surface, which can cause leaves to curl, yellow, or drop if the infection is severe. This pattern fits a wide range of plants, including lilac, crape myrtle, chrysanthemums, asters, strawberries, rosemary, and roses, making powdery mildew the likely cause of the white dusty layer.

Botrytis presents as a gray fuzzy mold on flowers and decaying tissue in damp conditions, not a clean white powder on healthy-looking leaves. White rust shows white or yellowish pustules on the undersides of leaves or stems in a more blister-like pattern. White powdery smut isn’t the typical description for common garden problems in these plants. So the white dusty layer described is most consistent with powdery mildew.