Downy Mildew

Rose Fungus Rose Bush Disease

Downy Mildew is a common rose fungus that will cause significant defoliation of your rose plants. This rose fungus is a rose bush disease, that affects roses throughout the U.S.

This disease is most prevalent in the Spring, in moist coastal regions of California, and the Pacific Northwest.

Symptoms of Downy Mildew;

Once the plant is affected with Downy Mildew, young leaves will develop dark purplish to dark brown spots on them. The spots/blotches are defined by leaf veins on the upper surface of the leaf. The symptoms of Downy mildew sometimes look like burns.

This disease is often confused with the disease (Black spot).

Infected leaves may turn yellow, and will often drop off quickly once the infection appears.Young shoots may wilt and die.

You should collect and discard all of the infected leaves but (Do not compost them)

Downy mildew can also affect the stems of the roses.

This rose fungus requires high humidity (over 85%) and cool temperatures to get started. Spring time is the perfect weather for this rose bush disease to take hold of the rose.

The best mildew control, involves trying to avoid the problem before it starts! You can do this by checking your plants regularly to identify the problem early on.

If your climate is moist with high humidity, you might begin a spraying as a preventative in early spring. The organic spray is a mixture of Baking soda, water and horticultural oil (or dish soap). Be sure to spray the undersides of the leaves. Early in the day is the best time to spray.

(As a rule, I never spray in the heat of the day or late afternoon).

This is one of the more common diseases of rose plants for those rose growers that grow cutting roses under glass, but not so much for garden roses.


To help you grow the best rose plants possible, with the least effort, follow recommendations on this site about Choosing Disease Resistant Roses ; Organic Roses ; and  Planting Roses

Good Garden Hygiene

What Causes Mildew on Plants?

Here are some tips for good garden hygiene that could help you avoid problems.

  • Choose disease resistant plants, and limit your plants from influences that help spread the disease.
  • Having good air circulation around the plants help to keep the plants dry, and keep disease spores at bay. Space plants so they are not to close to one another, keep them trimmed so that you do not allow them to grow in to one another as they get large.
  • Weed your garden! By keeping the garden weeded, you remove plants that harbor diseases such as roses mildew and black spot, as well as removing the breeding grounds for Japanese beetles and Leaf hoppers
  • Prune the rose bushes to remove diseased canes and leaves. Remember to always dispose of damaged leaves and canes in another area of your yard, away from healthy bushes
  • Water at ground level, to avoid wetting the leaves. If you must water from above, do it early enough in the day so that the leaves will have time to dry before night

Drip irrigation is the best way to water your roses. It puts the water right at the roots of the plants without the splashing that causes many problems for the rose bushes.

  • Keep the garden mulched. Mulching also prevents water from splashing onto plants and contaminating them with disease spores from the ground.

More Rose Diseases and Pests like Downy Mildew

Go To Black Spot on Roses

Go to Rose Aphids

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common rose disease black spot

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