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Populations of Aspergillus flavus in the Iowa Cornfield Ecosystem in Years Not Favorable for Aflatoxin Contamination of Corn Grain. D. C. McGee, Seed Science Center and Departments of Plant Pathology and Botany, Iowa State University, Ames 50011;. O. M. Olanya, and G. M. Hoyos, Seed Science Center and Departments of Plant Pathology and Botany, Iowa State University, Ames 50011; and L. H. Tiffany, Department of Botany, Iowa State University, Ames 50011. Plant Dis. 80:742-746. Accepted for publication 18 March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0742.

Populations of Aspergillus flavus were measured at monthly intervals from June to September in corn crop residues, corn leaf tissues, soil, and air over two periods, 1979 to 1980 and 1991 to 1993, in permanent tillage and rotation plots (64 ? 64 m) established at Nashua, IA, in 1977. A. flavus was detected in soil each year of the study. Tillage and rotation practices had little impact on soilborne populations of A. flavus, but significantly greater populations occurred in July in 1991 to 1993 than occurred in June, August, or September. The fungus was recovered at greater frequencies from corn residues of continuous corn plots than from corn grown in the soybean-corn rotation. Populations of A. flavus on leaves were unaffected by tillage or rotational practices. Airborne spores of A. flavus were detected in all plots in each year of the study, but tillage and rotation treatments had no significant effect on airborne populations. A survey of 40 Iowa cornfields over the period 1991 to 1993 that had aflatoxin-contaminated corn in 1988 showed widespread occurrence of A. flavus in soil and corn residues. Populations in these fields were of the same magnitude as those found at the Nashua plots. Assays for A. flavus from soil from these fields showed greater soilborne populations in July of 1993. This study indicates that A. flavus is widely distributed in the corn ecosystem in Iowa at very low population levels in years that are not favorable for extensive aflatoxin contamination of corn grain.

Keyword(s): Zea mays