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Control of Soilborne Pathogenic Fungi in Fields of Sweet Onion

August 1997 , Volume 81 , Number  8
Pages  885 - 891

Donald R. Sumner and Ronald D. Gitaitis , Coastal Plain Experiment Station , and J. Danny Gay , Rural Development Center, Department of Plant Pathology, Tifton, GA 31793-0748 ; Doyle A. Smittle (retired) , Department of Horticulture , and Bryan W. Maw , Department of Biological and Agricultural Engineering, Coastal Plain Experiment Station ; Ernest W. Tollner , Department of Biological and Agricultural Engineering, Athens ; and Yen Con Hung , Department of Food Science and Technology, Georgia Station, Griffin, University of Georgia

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Accepted for publication 17 April 1997.

Populations of soil fungi from fields planted to sweet onion were assayed on selective media. In pathogenicity tests, Rhizoctonia solani AG-4, Pythium irregulare, and Phoma terrestris were the fungi most virulent on onion seedlings. Plots were fumigated with methyl bromide (MBR), chloropicrin (CP), MBR + CP (67% + 33%), metam sodium, 1,3,-dichloropropene (1,3-D), or 1,3-D + 17% CP in four field experiments in 2 years. Sweet onion was transplanted or direct seeded in October or November and harvested in April or May. MBR + CP and CP were effective in reducing populations of Phoma terrestris, Pythium spp., Fusarium spp., and R. solani AG-4 in soil. Metam-sodium and 1,3-D + 17% CP were less efficacious, and MBR and 1,3-D were ineffective. There were no differences in the percentage of bulbs with decay at harvest or after curing among treatments. Increased yield of marketable bulbs was associated with control of soilborne pathogenic fungi. In fields continuously cropped to onion, decreased yield was primarily associated with control of pink-root induced by Phoma terrestris, and P. terrestris was identified in soil from 74% of the fields assayed.

Additional keywords: Aspergillus niger, Botrytis allii

© 1997 The American Phytopathological Society