pests and diseases
Powdery mildew
Last reviewed 2026-10-04
Powdery mildew is a group of fungal diseases that produces pale, powdery growth on leaves, stems, flowers, or fruit. Different fungi affect different hosts. The disease is often favored by crowded plants, poor air movement, shade, and humid conditions, although free water on leaves is not always required for infection.
What it means
The white coating is made of fungal growth and spores on the plant surface. Leaves may yellow, curl, or drop when infection is severe. The exact organism matters because a product or practice that works for one host may not work on another.
How it affects the garden
Start with prevention: choose a suitable planting site, provide spacing for air movement, water the root zone when practical, and remove badly affected plant material. Avoid handling plants while foliage is wet. Resistant varieties can reduce risk but are not immune under every condition.
Use an integrated approach instead of treating every white patch automatically. Confirm the diagnosis, consider whether the plant can tolerate the damage, and follow any product label exactly. The can I grow this tool helps evaluate site fit, but it is not a disease identifier.
Example
A dense squash planting develops white patches on older leaves during a humid period. Opening the canopy with proper spacing and removing severely affected leaves may reduce spread, but the result depends on the disease and weather.
Common confusion
Powdery mildew is not the same as dust, residue, or downy mildew. Downy mildew usually develops differently and requires different conditions and diagnosis.
Sources
University of Minnesota Extension describes powdery mildew symptoms and management.
