Black Root Rot

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 degrees 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 individual cells appear to snap apart.
• Light-colored spores are formed in a long tapering cell and extruded in chains

Managment

• Steam field soil and peat moss. Heat it to 180 degrees F and hold it at that temperature for 30 minutes.
• Apply thiophanate methyl (Clearys 3336*, Domain*, Banrot*, Fungo*, and SysTec 1998*) or triflumizole (Terraguard*) as a soil drench.

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, Minn. 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, N.C. 130 pp.