How to Manage Pests

Pests in Gardens and Landscapes

Downy mildew—Peronospora parasitica

Infections of downy mildew begin as irregular yellow patches on leaves; these chlorotic lesions later turn brown. If conditions are favorable, white fluffy growth of the fungus develops on the undersides of leaves. Leaves may take on a blighted appearance. Systemic infections can cause internal black streaks and patches to form in stems and floret branches of broccoli and cauliflower.

Identification | Life cycle

Solutions

The best way to prevent downy mildew is to avoid the environmental conditions that favor it. Freely circulating air, allowing plants to dry between irrigations, and keeping leaves as dry as possible are good ways to limit the disease. Cool, moist weather in early spring and late fall favor the disease, so adjusting planting times may help in some areas. Destroy infected crop debris and susceptible related weeds before planting a new crop. Resistant broccoli varieties are available.

Spots caused by downy mildew on broccoli
Spots caused by downy mildew on broccoli

Infected cauliflower beneath cortical tissue
Infected cauliflower beneath cortical tissue


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

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