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Influence of Isolates of Gliocladium virens and Delivery Systems on Biological Control of Southern Blight on Carrot and Tomato in the Field. JEAN B. RISTAINO, Associate Professor, North Carolina State University, Raleigh 27695-7616. JACK A. LEWIS and ROBERT D. LUMSDEN, USDA-ARS, Biocontrol of Plant Diseases Laboratory, Beltsville Agriculture Research Center, Beltsville, MD 20705. Plant Dis. 78:153-156. Accepted for publication 27 October 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0153.

Experiments were conducted in the field from 1990 to 1992 to evaluate the influence of two isolates of the fungal antagonist Gliocladium virens and two delivery systems on the biological control of southern blight caused by Sclerotium rolfsii on processing carrot and tomato. Two isolates of G. virens (GL-3 and GL-21) in either a bran prill or vermiculite bran formulation, nonamended control formulations, and the fungicides PCNB (Terrachlor 75WP) or flutolanil (Moncut 50WP) were applied to separate plots infested with 5. rolfsii arranged in a randomized complete block design. The incidence of southern blight in carrot was consistently reduced over 3 yr by both isolates of G. virens in the bran prill formulation when the antagonist was cultivated into soil on both sides of the row. Disease control on carrots with the bran prill formulations of G. virens was equal to or better than control achieved with the fungicides PCNB and flutolanil. Respective disease incidences in 1990, 1991, and 1992 on carrots were 62, 65, and 35% in S. rolfsii-infested control plots; 4, 46, and 12% in GL-3 bran-prill-amended plots; and 23,48, and 11 % in GL-21 bran-prill-amended plots. Disease control with the vermiculite bran formulations of the same two isolates was more variable on carrot over the years but was obtained in 1990. Yield of carrot was increased in plots treated with bran prill formulations of GL-3 and GL-21 compared with 5. rolfsii-infested controls. In contrast, significant reductions in disease incidence on processing tomato were only observed in 1991; disease incidence was reduced from 69% in nontreated control plots to 27% in plots treated with the bran prill formulation of isolate GL-3. Biological control of southern blight may be more feasible on carrot, which has a more limited infection court of the taproot and stem, than on processing tomato, which has a large infection court including roots, stems, leaves, vines, and fruit. These results demonstrate that biological control is a viable alternative and equally efficacious to chemical control for southern blight of carrot.