How to Manage Pests

Pests in Gardens and Landscapes

Seasonal development and life cycle—Downy mildew

Downy mildew can develop very quickly from an initial infection into an epidemic spread by airborne spores if humidity and temperature conditions are favorable (1.5 - 7 hours of leaf wetness and 43° - 80° F). Spores can travel long distances in moist air, but are quickly killed by dry conditions. Initial sources of disease can be infected bulbs, sets, seeds, and plant debris.

Spores on onion leaf
Spores on onion leaf


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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