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.
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Sclerotia
and white mycelium on bulbs |
