Downy Mildew
(fungus - Peronospora sparsa): A highly destructive disease on rose, causing
severe and rapid defoliation. The fungus is active only under cool, damp conditions.
Leaf symptoms vary from angular blotches (yellow, purple to brown) to a scorch
like burn. Downy mildew has not been a problem in landscapes in Texas. It has
on occasion developed in commercial operations where roses are grown temporarily
in containers. Regular overhead watering and thick growth from close spacing create
ideal conditions for this disease. Preventive fungicides should be applied when
weather is ideal for disease development.
