Diagnosis
Diagnose: Watermelon Powdery Mildew
Use these observations to decide what to check next.
Look for expanding surface colonies on older leaves
Powdery mildew begins as separate white patches that merge into a dusty coating on upper and lower leaf surfaces and petioles. Normal rind or leaf pattern stays within the tissue, spray residue follows droplets, and downy mildew starts with angular yellow lesions bounded by veins rather than a uniform floury film.