Powdery Mildew Questions

by Nirmala
(Brooklyn, NY)

Hi Annelie,
I wrote to you before and you suggested getting the America climbing rose. I received the plant and planted it in April. Unfortunately, it has mildew. I read up on your advice and have a few more questions.
Is Neem oil the horticultural oil to which you refer?
Are 'affected' leaves only those covered in mildew or do I consider curly leaves without mildew 'affected'?
If both need to be removed, I'm worried about my small plant which would be left with few leaves. The ones that don't have mildew have black/brown spots.
There is new growth, even without fertilizer, which I will begin soon. As you know, the new growth is what is affected. Should I do a full cut-down right away?
Thank you,
Hi Nirmala,
Horticultural oils are highly refined petrolium oils combined with an emulsifying agent, sometimes in combination with plant derived oils, such as Neem oil.
The most important effect of horticultural oils is that they block the air holes through which insects breathe, causing the insects to die from asphyxiation.
The oils also control plant diseases such as powdery mildew by killing the fungus spores.
The oils are safe to use and pose few risks to people including beneficial insects.
You should remove all infected leaves, even the curled up ones and spray the canes and remaining leaves, as well as the soil around the roses, with the horticultural oil.
Your rose will eventually recover, because powdery mildew is not fatal.
The rose will take time to regain energy to grow more foilage.
Do not fertilize the roses at this time, just keep them watered and well hydrated.
Scratch in about half a cup of Epson Salt around the roses and water deeply.
And then add a couple of inches of organic mulch to the soil
The black/brown spots on the other roses are caused by black spot which is another fungus disease.
Best Regards,

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