Planning reference

Powdery Mildew vs Downy Mildew

Compare powdery mildew and downy mildew by leaf surface, humidity, leaf wetness, airflow, crop family, watering method, and response timing.

What each mildew clue can mean

Powdery mildew
Powdery mildew usually shows as a white powdery coating or pale spots on upper and lower leaf surfaces, especially on cucurbits and other susceptible crops as plantings mature.
Downy mildew
Downy mildew usually starts as yellow to pale green angular leaf spots, with velvety gray fuzz or dark purplish-gray growth on the underside of leaves in humid conditions.
White powdery coating
White powdery coating points more strongly toward powdery mildew than downy mildew, but crop family and both leaf surfaces still need to be checked.
Velvety gray fuzz
Velvety gray fuzz on the lower leaf surface, especially with angular yellow spots, is a downy mildew warning sign on cucumbers, melons, squash, and related crops.
Wet or very humid conditions
Wet or very humid conditions favor downy mildew, while powdery mildew can spread in warm, dry periods and crowded or shaded plantings with poor airflow.

Decision workflow

Inspect both leaf surfaces
Do not treat every white, yellow, or fuzzy leaf problem the same; check the crop family, upper and lower leaf surfaces, recent humidity or leaf wetness, airflow, spacing, watering method, and disease alerts before removing plants or using sprays.
Separate coating from underside fuzz
A powdery coating across leaf surfaces points to powdery mildew; angular yellow spots plus underside fuzz points to downy mildew or another leaf-spot problem.
Check water and airflow
Crowding, weeds, shade, overhead watering, and poor air movement can make leaf disease harder to manage, but the best response depends on which mildew is present.
Use resistant varieties when possible
If mildew has been a repeated problem, prioritize resistant varieties and crop-family fit before expecting spacing or sprays to solve everything.
Remove plants only when justified
Downy mildew guidance can include removing symptomatic plants, while powdery mildew management may focus first on resistant cultivars, airflow, debris cleanup, and labeled options when needed.

Use these paths

Source basis