Fusarium Crown and Root Rot of Tomato in Greenhouse Rock Wool Systems: Sources of Inoculum and Disease Management with Benomyl. L. Mihuta- Grimm, Research Assistant, Department of Plant Pathology and Horticulture, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. W. A. Erb, and R. C. Rowe. Assistant Professor, and Professor, Departments of Plant Pathology and Horticulture, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 74:996-1002. Accepted for publication 4 June 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0996.

Fusarium oxysporum f. sp. radicis-lycopersici grew equally well on sterile rock wool growth substrate saturated with either sterile distilled water or plant growth solution but was completely suppressed by the addition of low concentrations of benomyl (0.023, 0.045, and 0.090 g a.i./L). In greenhouse studies using a hydroponic rock wool system, tomato plants that originated from infected transplants developed severe symptoms of Fusarium crown and root rot at the end of the season and had significantly lower yields than controls. Disease also developed in plants exposed to soil infested with F. o. f. sp. radicis-lycopersici, but little disease developed when a dilute conidial suspension of the pathogen was added to the rock wool system. Uninfected plants growing in the same rock wool production slab as infected plants did not develop substantial disease symptoms during any greenhouse test. Three-week-old seedlings treated with drenches of benomyl at dilutions ranging from 0.023 to 0.138 g a.i./L developed moderate to severe chlorosis. At the higher rates, phytotoxicity symptoms were more severe and often included stunting. Application of benomyl at 0.090 g a.i./L on a 21-day schedule to plants growing on rock wool production slabs resulted in optimal disease control. Our results suggest that production of disease-free transplants is of utmost importance for controlling Fusarium crown and root rot of tomato.