Effects of Fallow and of Summer and Winter Crops on Survival of Wheat Pathogens in Crop Residues. Myriam R. Fernandez, Research Station, Agriculture Canada, P.O. Box 1030, Swift Current, Sask. S9H 3X2. J. Mauricio Fernandes, and John C. Sutton. Centro Nacional de Pesquisa de Trigo, C.P. 569, Passo Fundo, Rio Grande do Sul, 99.010 Brazil; and Department of Environmental Biology, University of Guelph, Guelph, Ont. N1G 2W1, Canada. Plant Dis. 77:698-703. Accepted for publication 19 March 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0698.

Survival of Fusarium graminearum, Cochliobolus sativus, and Leptosphaeria nodorum in wheat, corn, and soybean residues was studied in field plots in southern Brazil during 1988 and 1989. Wheat was harvested in November 1987 and 1988 and was followed by various summer and winter crops or by summer or winter fallow. In 1988, incidence of the three pathogens in the wheat residues was high (70–90%) until April for C. sativus and L. nodorum and until July or October for F. graminearum, then declined progressively. L. nodorum had the least ability of the three to survive in wheat residues over time. In both 1988 and 1989, F. graminearum and C. sativus, but not L. nodorum, were detected in wheat residues at the final sampling time (December), about 14 mo after the wheat was harvested. In 1988, the three pathogens survived longer in the wheat residues after summer fallow than after corn or soybean crops, but there was no difference in the incidence of F. graminearum and C. sativus among winter treatments that followed soybean or corn. In general, the densities of propagules of C. sativus and F. graminearum in the wheat residues started to decline earlier than their frequency. The three pathogens were also isolated from soybean residues, and F. graminearum and C. sativus were isolated from corn residues.