Black Root Rot (Thielaviopsis)
Gary W. Moorman, Professor of Plant Pathology
The fungus Thielaviopsis basicola (Berk. & Br.) Ferraris is a soil inhabiting fungus that can cause root rot and branch dieback on a number of woody and herbaceous plants including holly, begonia, geranium, poinsettia, cyclamen, gerbera, and pansy. Soil temperatures between 55 and 65°F generally favor this fungus, particularly if the soil is wet. The fungus can be found in field soil but has also been found associated with commercial peat moss.
- stunting of foliage and root systems
- blackened areas on roots
- yellowing of leaves between the veins or along the margins
- branch dieback
- dark brown, multicelled spores form in the infected roots. The indivudual cells appear to snap apart.
- Light colored spores are formed in a long tapering cell and extruded in chains
- Steam field soil and peat moss. Heat it to 180°F and hold it at that temperature for 30 minutes.
- There are some very effective fungicides for use in managing this plant pathogen. Check with Cooperative Extension or the Pennsylvania Department of Agriculture to determine what is currently available for use.
Holly: Ilex crenata, Helleri, Hoogendorn, Nigra, Green Cushion, Mobjack Supreme and Hetzzi are very susceptible. Ilex vomitoria and Ilex opaca are moderately resistant. English holly (Ilex aquifolium) and Chinese holly (Ilex cornuta) are highly resistant.
Daughtrey, M. L., Wick, R. L., and Peterson, J. L. 1995. Compendium of Flowering Potted Plants. APS Press. St. Paul, MN. 90 pp.
Lambe, R. C. And McRitchie, J. J. 1986. Holly diseases. In, Diseases of Woody Ornamental Plants and Their Control in Nurseries. North Carolina Agricultural Extension Service, Raleigh, NC. 130 pp.
Thielaviopsis spores in culture
In a root cell
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Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
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