How to Manage Pests

Pests in Gardens and Landscapes

Downy mildew—Peronospora destructor

The first evidence of downy mildew is a fine, furry, grayish white to purple growth on the surface of older leaves. Leaf tissue under the growth becomes pale green, then yellow, and finally collapses. Large, yellowish, circular clumps of infected plants may be the first symptom noticed in the garden. The yellowing patterns often enlarge in the direction of prevailing winds.

Life cycle

Solutions

Use disease-free bulbs, sets, and seed. Use a 3-year rotation away from onions, garlic, and related crops where the disease has occurred. Destroy volunteer and diseased plants. Well-drained soil, freely circulating air, and allowing plants to dry between irrigations help prevent the disease.

 

Purplish growth of downy mildew
Purplish growth of downy mildew


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