How to Manage Pests

Pests in Gardens and Landscapes

Downy mildew—Bremia lactucae

Downy mildew causes light green to yellow angular spots on the upper surfaces of leaves. White fluffy growth of the fungus develops on the underside. With time these lesions turn brown and dry up. Older leaves are attacked first. Severely infected leaves may die. On rare occasions the pathogen can become systemic, causing dark discoloration of stem tissue.

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 cultivars are available.

Yellow spots on upper surface of leaf
Yellow spots on upper surface of leaf

Fungal growth on underside of leafFungal growth on underside of leaf

 


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