Thielaviopsis or black root rot

Root and stem rots

Pathogen

Thielaviopsis basicola.

Hosts include

Digitalis, Gaillardia, Geranium, Lathyrus, Lupinus, Pachysandra, Phlox and Viola.

Geranium thielaviopsis
Infected geranium with poor vigor and dieback symptoms.

Symptoms

Stunting, yellowing and plant death. Symptoms are often mistaken for nutrient deficiency symptoms.

Phlox thiel
Yellowing of phlox foliage caused by black root rot.

Spread

Thielaviopsis basicola produces spores that can persist for long periods of time in soil or on infested pots and equipment.

Digitalis with thielvaiopsis Digitalis thielaviopsis root rot symptoms
Chlorotic foliage caused by Thielaviopsis basicola. These symptoms are easily mistaken for a nutrient deficiency. At right, infected roots are darkly colored and rotted by black root rot.

Reusing contaminated equipment is a common source of disease. Fungus gnats and shore flies can vector spores.

Management

Do not reuse plug trays, flats or pots for susceptible crops. Keep good records of the production areas where there have been problems with T. basicola. Avoid growing susceptible crops in these areas for several years. Fungicide drenches should be used to protect very susceptible plants from infection.

Conidia on root
Darkly colored spores of Thielaviopsis basicola have a distinctive morphology. Their thick spore wall helps them persist for several years in soil.

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