Powdery Mildew on Roses

Powdery mildew on roses appears as a white powdery mold on the leaves and buds. After contracting powdery mildew roses will drop their leaves prematurely. Take precautions to prevent rose mildew from spreading to your fruit trees.



Powdery Mildew on Rose Leaf Caused by Sphaerotheca Pannosa
Powdery Mildew on Rose Leaf Caused by Sphaerotheca Pannosa

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Geoff, Kidd
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Rose mildew is one of the most common rose diseases. It is caused by several different fungi, Sphaerotheca pannosa being the most problematic as it can spread to and infect stone fruits growing near mildew infected roses.

Powdery mildew in roses will cause the leaves to pucker and wrinkle. Premature leaf drop is another symptom.

The best control is prevention.

Choose resistant rose varieties or at least avoid planting vulnerable varieties near stone fruits.

Powdery Mildew (Sphaerotheca Pannosa) on a Rose Bud (Rosa)
Powdery Mildew (Sphaerotheca Pannosa) on a Rose Bud (Rosa)

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Cattlin, Nigel
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Causes of Roses Powdery Mildew

  • Lack of air circulation around the plants.

  • Insufficient watering.

  • Lack of soil nutrients.

  • Hot days followed by cool nights.
  • Roses growing in less than all day sun will be more vulnerable. Avoid overcrowding the plants. Use drip irrigation to water and avoid wetting the foliage as this can splash the spores onto other roses nearby.

    Lime-sulfur sprays are effective against rose powdery mildew. Spray susceptible plants before growth begins in the spring. Reapply the control weekly during the growing season.

    Avoid spraying the plants while the sun is on them or when temperatures exceed 85 degrees F. to prevent leaf burn.

    Ortho Rose Pride is a 3-in-1 product that will protect against black spot, rust, and powdery mildew on roses. This provides a much better value than buying separate products for each disease.

    If you would prefer an organic fungicide, Green Light is the one I recommend. The active ingredient is neem oil. It will control black spot, powdery mildew, rust, anthracnose, spider mites, aphids, and whitefly.

    If you would like to try a homemade rose mildew spray, here is a recipe:

    1. Into a clean, dedicated quart spray bottle of warm water add 1 tablespoon of baking soda and a few drops of dish washing liquid.
    2. Shake the mixture gently until the baking soda dissolves.
    3. Spray this on the rose leaves (both sides) in the early morning or evening.

    I have never tried this but the theory is that the baking soda raises the pH of the leaf surface making it inhospitable to the growth of mildew spores.



    Downy Mildew on Roses
    Description and control of downy mildew on roses. Peronospora sparsa is the fungus that causes this type of rose mildew. Control of downy mildew is effected with different chemicals than those used against powdery mildew.

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    The Green rose, Rosa chinensis viridiflora, is an old heirloom China rose. Its green colored rose are the result of a chance mutation. The petals of this green rose flower are actually sepals.

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    Sunny Knockout Rose Tree
    from: Fast Growing Trees Nursery

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