Downy mildew starts as small angular yellow spots on the leaves
The yellow angular spots will turns purple in color. At the advanced stage of the infection brown dead areas can be sen within the purplish blotches.
In severe cases purplish patches can be seen on the branches. Under favorable conditions, spore masses can be seen on the lower surface of the leaves and on canes. All cultivated roses are susceptible to downy mildew including Knock Out®