Submitted to: Phytopathology Supplement; APSnet (Plant Pathology Online)
Publication Type: Abstract Only
Publication Acceptance Date: 4/12/2005
Publication Date: 4/12/2005
Citation: Dugan, F.M., Hellier, B.C., Lupien, S.L. 2005. Efficacy of fungicides against infections of garlic in Washington state [abstract]. Joint Meeting of the Western Soil Fungus Conference and the American Phytopathological Society - Pacific Division, Schedule and Abstracts, June 28 - July 1, 2005, Portland Oregon. Interpretive Summary: The USDA-ARS Western Regional Plant Introduction Station (WRPIS) acquires, maintains, evaluates, stores and distributes cultivars of garlic to growers and scientists. During 2001-2003, diseases of garlic caused serious losses during harvest and storage. Three fungi were primarily responsible: Fusarium oxysporum f. sp. cepae, Fusarium proliferatum and Embellisia allii. All three are distributed world wide and are capable of surviving in soil and in stored garlic. We conducted trials with two fungicides, fludioxonil and thiophanate methyl, and compared their efficacy to benomyl, a fungicide formerly widely used but no longer commercially available in the United States. When used as a dip for cloves prior to planting, fludioxonil and thiophanate methyl were effective in promoting plant health, as was benomyl, but effectiveness was somewhat inconsistent. When used as a post-harvest dip for bulbs, thiophanate methyl and benomyl were equally effective in preventing rot. Our preliminary experiments indicate that fludioxonil and thiophanate methyl can be effective as pre-planting dips, and that thiophanate methyl can be effective as a post-harvest dip, provided that infections are not already too deeply established in host tissues. Fludioxonil and thiophanate methyl have different modes of action, so use alternate use of these fungicides may inhibit fungicide resistance.
Technical Abstract: Fusarium proliferatum, F. oxysporum f. sp. cepae and Embellisia allii caused serious losses in 2001-2003 during garlic (Allium sativum) regeneration and storage for the National Plant Germplasm System in Pullman, Washington. When fludioxonil, thiophanate methyl or benomyl were used as pre-planting dips for cloves planted to the field, mean bulb weights in each treatment were higher than controls, but significantly so only for fludioxonil and thiophanate methyl. When these fungicides were used as pre-planting dips with soil artificially infested with the pathogens in a greenhouse, mean plant weights for fungicide treatments were again higher than controls, but results were significant only for benomyl. When benomyl and thiophanate methyl were used as post-harvest dips of bulbs from field soil, both were equally and significantly effective in reducing the mean fraction of cloves rotted per bulb. Deep-seated, artificial infections of cloves were not affected by fungicides even with dip times up to 180 minutes. Survival of the Fusarium spp. in field soil was confirmed by bioassay with a susceptible onion variety. Thiophanate methyl and fludioxonil have different modes of action, and may be as effective as benomyl as pre- and/or post-harvest dips for managing Fusarium and Embellisia diseases of garlic.