Predisposition of Soybean Seedlings to Fusarium Root Rot with Trifluralin. M. L. Carson, Associate Professor, Plant Science Department, South Dakota State University, Brookings 57007. W. E. Arnold, and P. E. Todt. Professor, and Former Graduate Research Assistant, Plant Science Department, South Dakota State University, Brookings 57007. Plant Dis. 75:342-347. Accepted for publication 14 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0342.

Soil-incorporated trifluralin significantly increased the severity of Fusarium root rot of soybean seedlings (Glycine max ‘Corsoy’) in greenhouse and field trials. Hypocotyl swelling and cracking caused by trifluralin appeared to offer favorable sites for penetration by Fusarium oxysporum. Exposure of soybean seedlings to trifluralin before being transplanted to pathogen-infested soil also resulted in an increase in root rot severities. The predisposing effect of trifluralin decreased with increasing soil temperatures. No consistent in vitro effects of trifluralin on growth or reproduction of F. oxysporum were observed. These data support the hypothesis that the primary effect of trifluralin on the host-pathogen interaction is to predispose soybean seedlings to infection by F. oxysporum.