Double Knock Out Rose -- Diseases.
(Lafayette, Louisiana, USA)
QUESTION: I have two Red Double Knock Out Rose Bushes.
I read that they are very disease resistant.
I have given the bushes a trimming about a month ago.
Then I put some Miracle Grow Rose Food.
New growth was seen quite soon following this trimming event.
However, now almost a month after, I am noticing that the new maroon colored leaves seem to be suddenly dulling in color.
It almost looks like there is a faint whitish/greyish hue on the leaves.
A few of the leaves are yellowing too! There are a lot of blooms.
Please advice what next steps need to be taken.
ANSWER: You garden in a region that has problem with fungus disease.
You double knock out rose has been infected by powdery mildew, which is common rose plant disease coused by fungus (Sphaerotheca pannosa).
It is one of the most serious and widespread diseases for roses.
I recommend you spray with Ortho's RosePride Rose & Shrub Disease Control.
Follow directions per label, and repeat the spray at intervals of 7 to 10 days if mildew reappears.
Rake and destroy leaves during infestations and in the fall.
I know the knock out roses are very resistant, but if it's a severe infestation, they will be affected.