How to Treat Downey Mildew on Roses

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By Lee Ann Lambert
eHow Contributing Writer

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Even seasoned gardeners get downy mildew on their roses. This disease affects roses in all regions, and is caused by the Peronospora sparsa fungus, with the help of wet, cloudy weather and temperatures between 65 and 75 degrees. The infection starts on new plant growth and can leave a rose plant bare of leaves within a few short days.

While downy mildew on roses is a serious problem that can cause plant death, measures can be taken to save the affected roses and prevent the spread of downy mildew and further outbreaks.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

Garden gloves
Pruners
Hand sanitizer or bleach
Rake
Yard waste bags
Fungicidal soap

Step 1

Prune all of the rose plants that are infected with downy mildew, removing any buds, canes and stems that are affected. Sanitize your pruners before moving on to the next plant. Dip a clean rag in hand sanitizer or a mild bleach and water solution, and rub the blades of the pruners with it. Dry the pruners before continuing.
Step 2

With a rake or by hand, clean all debris, including fallen leaves, rose buds, petals, cut canes and stems from the area surrounding the rose bush. Take care to remove every bit of affected plant material as the downy mildew fungus spores can stay active for up to a month and reinfect the plant or surrounding plants. Place the debris in a yard waste bag to be taken away, or put the debris in the garbage.
Step 3

Spray your rose bushes with a fungicidal soap every seven to 10 days to protect them from further outbreaks of downy mildew.

Tips & Warnings

Roses need good air circulation around them to help prevent downy mildew and other diseases. Plant your roses so that they will have at least two feet of clear space on all sides when they are of mature size. Roses require full sun to thrive. Being in a sunny spot also helps prevent mildew. Never use overhead watering for roses. Only water the soil, using care to not get the leaves, flowers and canes wet. When choosing roses, pick ones that are advertised as disease resistant. This doesn't mean the rose will never be affected by downy mildew, only that it has better resistance to it.