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.
Symptoms
- stunting of foliage and root systems
- blackened areas on roots
- yellowing of leaves between the veins or along the margins
- branch dieback
SIGNS
- 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
Management
- Steam field soil and peat moss. Heat it to 180°F and hold it at that temperature for 30 minutes.
- Apply thiophanate methyl, thiophanate methyl + etridiazole, fludioxonil, or triflumizole as a soil drench. When using thiophanate methyl, it is best to have the pH between 6 and 8 in the drenching liquid.
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.
References
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.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade names (EPA Reg. no.) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807) |
| Fungo Flo (51036-329-59807) | |||||
| Systec 1998 (48234-12) | |||||
| 3 | 2 | Imidazole | triflumizole | 12 | Terraguard (400-433) |
| myclobutanil | 24 | Systhane (707-253) | |||
| 12 | 2 | Phenylpyrol | fludioxonil | 12 | Medallion (100-769) |
| Combined 1 products | |||||
| 1 + M | thiophanate methyl + etridiazole | Banrot (58185-10) |
Thielaviopsis spores in culture
In a root cell
DISCLAIMER
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
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.
Visit Penn State Extension on the web at extension.psu.edu.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/TTY.
