Diseases of onion and garlic(
White rot
White rot is caused by the soil borne fungus Sclerotium cepivorum. Foliage symptoms are not apparent until the fungus grows into the bulb of the plant. Foliage symptoms include yellowing, leaf dieback and wilting. Older leaves are affected at first, followed by stunting of plants and death of all foliage. Root rot also occurs. Plants may suddenly die in large areas of the field if the soil is heavily infested.
Disease development occurs when soil is moist and cool, and disease is significantly inhibited above 78° F. A white fluffy growth, which is the mycelium of the pathogen, develops around the base of the bulb and eventually colonizes the entire bulb. Small sclerotia about the size of a poppy seed form in decaying tissues. The sclerotia resist decay and can remain in the soil for over 20 years. Sclerotia can be spread within a field or from one field to another by surface water, farming equipment or infested plant material.
The best control for white rot is to prevent the introduction of Sclerotium
cepivorum into garlic and onion fields by practicing meticulous
sanitation measures. Plant garlic seed cloves from origins that
have no history of white rot. Always clean equipment before moving
from one onion or garlic field to the next. If a field becomes
infested with the pathogen, do not plant onion or garlic there again.
Crop rotation will not control white rot; however, it will prevent an
increase in the population of sclerotia. Soil fumigation with
methyl bromide or metam sodium as well as soil flooding and soil solarization
have been shown to reduce the population of viable sclerotia in infested
soil.
February 10, 2003