How to Manage Pests

Pests in Gardens and Landscapes

Downy mildew of roses—Peronospora sparsa

Downy mildew causes purplish, red, or dark brown spots on leaves. Leaf undersides are covered with downy fungal growth. Leaves may yellow and drop. The fungus that causes downy mildew on roses produces spores only on living plants. Resistant spores carry the fungus over unfavorable periods. Downy mildew is favored by moist, humid conditions.


Prune plants to improve air circulation. Reduce humidity around plants, by using, for instance, drip or low-volume irrigation. Avoid overhead watering. Fungicide applications help prevent damage.

Purplish spots on rose leafPurplish spots on rose leaf



Statewide IPM Program, Agriculture and Natural Resources, University of California
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