How to Manage Pests

Pests in Gardens and Landscapes

Seasonal development and life cycle—White rot

The pathogen persists as small, dormant structures, called sclerotia, in soil. Sclerotia can survive for over 20 years, even in the absence of a host plant. Disease severity depends on sclerotia levels in the soil at planting. As few as one sclerotium per 10 kilograms of soil can result in disease; one sclerotium per kilogram of soil, measurable disease loss; and ten to twenty sclerotia per kilogram, infection of essentially all plants.

Sclerotia can be spread by irrigation water or on plant material, including wind-blown scales. Sclerotia remain dormant in the absence of onion or other related crops.

Disease development is favored by cool, moist soil conditions. The soil temperature range for infection is 50° to 75° F, with optimum at 60° to 65° F. At soil temperatures above 78° F, the disease is markedly inhibited. Soil moisture conditions that are favorable for onion and garlic growth are also ideal for white rot development.

Sclerotia and white mycelium on bulbs
Sclerotia and white mycelium on bulbs

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