Influence of Cultural Practices, Fungicides, and Inoculum Placement on Southern Blight and Rhizoctonia Crown Rot of Carrot. R. S. Gurkin, Graduate Student, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. S. F. Jenkins, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 69:477-481. Accepted for publication 12 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-477.

The influence of disking and deep plowing, layby and no-layby cultivation, and times and rates of fungicide application on the development of southern blight, caused by Sclerotium rolfsii, and Rhizoctonia crown rot, caused by Rhizoctonia solani, on processing carrots in North Carolina was investigated. Deep plowing combined with no-layby cultivation effectively reduced southern blight of carrot. Layby cultivations negated the beneficial effects of deep plowing. Fungicides used for control of southern blight were effective for layby carrots in deep-plowed soil and for both layby and no-layby carrots in disked soil. The development of Rhizoctonia crown rot of carrot was not changed significantly by land preparation and cultural practices. The 2× recommended rates and multiple applications of PCNB, furmecyclox, and carboxin provided greater crown rot control than did 1× recommended rates and single fungicide applications. Infection of carrots by S. rolfsii on colonized oat grains occurred from greater lateral distances and depths than infection by naturally produced sclerotial inoculum. The highest level of infection by naturally produced sclerotia occurred when sclerotia were in contact with the carrot storage root.

Keyword(s): Daucus carota var. sativa, southern stem rot, southern wilt.