Hi Skiekitty,
Downy Mildew is a very common disease of Roses which occurs under "Moist Cloudy Conditions". The disease is found throughout the United States, Europe and South America. All species of cultivated and wild rose seem to be susceptible.
SYMPTOMS:-
Under cool and moist spring conditions, young leaves stems and
flowers may manifest purple to red or brown irregular spots. As the disease advances, lesions on leaves become angular and black with the possible appearance of white mycelium on the underside of the leaf. Advanced infections will have yellowing of leaves with brown necrotic areas and noticeable leaf abscission. As the scientific name indicates, the production of spores is sparse and therefore this disease is difficult to diagnose. Along the coast of California where moist cloudy conditions persist through summer, the disease is severe and can occur on large canes as purple irregular blotches
-Downy mildew appears on our garden roses only when these ideal, or at least very favorable, conditions are present.
They are:
Humidity over 85%
Temperatures under 80°
Downy Mildew Color-Black, Purple, Dark Red(leaf)
Powdery Mildew Color-White(Young Leaf)
