How to Manage Pests

Pests in Gardens and Landscapes

Downy mildew—Peronospora sparsa

Downy mildew initially causes a yellow discoloration on the upper leaf surface that progresses to red and purple. Lesions are often angular, restricted by veins. Light pink to tan areas and white spore masses may be present on the lower leaf surface. Leaves may show a mosaic of small yellow and red angular lesions as well as distortion. Fruit is dry, shriveled, and split.


The downy mildew fungus overwinters in roots and shoots and grows into new growth in spring. If possible, avoid planting in sites with a history of the disease. Roses and wild blackberries are alternate hosts for the disease. Once the planting is established, remove suckers and weeds to reduce humidity at the base of the plant. Remove affected plants and destroy old fruited canes after harvest. Copper sprays may be applied to protect developing fruit, flowers, and foliage from infection when conditions are wet.

Reddish blotched of mildew along veins
Reddish blotched of mildew along veins

Fruit symptoms on boysenberry
Fruit symptoms on boysenberry

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