How to Treat Tomato White Mold (Sclerotinia)

Referred to as timber rot, white mold, or sclerotinia stem rot, this disease can wreak havoc on tomato plants in cold, wet climates, and may persist in the soil for up to 10 years.

And it’s not only your tomatoes that may be at risk. White mold can infect more than 400 species of plants, including such important crops as potatoes and peppers.

Caused by the fungal pathogen Sclerotinia sclerotiorum, this disease is widespread in sub-tropical and temperate areas. Over 60 names have been used to date to refer to diseases caused by this pathogen.

Not surprisingly, it can also infect a large number of weeds, which can serve to maintain a reservoir of the pathogen.

Weed hosts include lamb’s-quarter, pigweed, Canada thistle, wild mustard, hairy nightshade, and ragweed – a who’s who of prominent weeds.

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A classic symptom of this disease is the production of structures called sclerotia that give the organism its scientific name. These survival structures look like rat droppings – small, black, hard, cylindrical objects.

The sclerotia form in or on dead plant tissue. You can find them inside tomato tissue that has turned white and dry due to the disease. This symptom in tomatoes gives the disease its alternate name, timber rot.

The first sign of infection by this pathogen is at the base of the main stem at the soil line or on lower branches. At first, the disease manifests as watery soft rots and bleached areas on the leaf axils and stems.

Next, a white fuzzy mold grows both inside and outside the plant. It then spreads to the flowers, petioles, leaves, and stems. The fruit can also be infected, turn gray, and