White rot activity is primarily mediated by soil temperature. Symptomatic plants will rapidly die. Below ground, look for small, poppy-seed sized sclerotia to cover the decaying storage leaves and bulbs. At the margins of patches, storage leaves and bulbs will have some or a lot of fluffy, white mold from the stem plate upward, but not extending above ground. Contact me or your garlic or onion company field person if you suspect white rot occurrence.
Positive diagnosis is essential.
This season, most of the garlic grown in central Oregon will be inspected for white rot by the Oregon Department of Agriculture. As white rot infestations are permanent and can be spread to other fields, growers need to learn the proper responses. Spot fumigation is useful for small, localized occurrences, but larger occurrences are not easily treated. Fusarium basal rot, incited by Fusarium roseum culmorum also kills garlic from the stem plate upward, with the same leaf flagging symptoms as both white rot and Botrytis porri. As this disease is almost totally clove-borne, little can be done to influence the disease once the crop is planted.