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.
• 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.