White Mold

White mold, also known as lettuce drop, tomato timber rot, and Sclerotinia stem and crown rot, is a collection of infections that can affect several garden plants. And they kill

Crown rot is also known as white mold in some regions, but that is something else entirely.

Rotting lettuce (Rasbak) CC BY-SA 3.0

White mold (Sclerotinia spp.) can remain dormant in the soil for years. It takes a significant amount of cool, moist temperatures to wake these fungi up from their dormancy. But the underside of a head of lettuce, or a cabbage, provides the perfect humidity needed to trigger an awakening and an ensuing infection.

Symptoms of white mold

Wilting is often the first symptom of white mold. You may see pale brown, woody lesions that girdle lower stems, causing wilt. And which may ultimately kill the plant.

Affected plant tissue develops watery lesions as cottony white mycelia form on the surface. Mycelia are the vegetative part of a fungus, made up of threadlike hypha. These white fungal growths appear on outer leaves, lower stems, and bean pods. White mold starts at the base of a plant and spreads, causing outer leaves to wilt and fall away while remaining attached. Garbanzo beans are particularly likely to become infected in the crown area.

White mold on bush bean (Rasbak) CC BY-SA 3.0

As damaged tissue dies and dries up, it will turn white and look bleached. Tiny (0.25–0.5 inch) irregularly shaped black flecks called sclerotia can be seen on and inside dead stems. Sclerotia are the resting body of the fungi, made up of a cluster of hyphal threads. These structures can remain dormant for a surprisingly long time.

White mold host plants

Along with lettuce and tomatoes, the legume, nightshade, and cabbage family members are susceptible to white mold. Other broad-leafed plants and many weeds can also become infected.

How to avoid white mold in the garden

Since prolonged moisture is needed for this fungus to come among us [sorry, I couldn’t resist], keeping things dry is a good defensive plan. These specific steps can help you avoid a white mold problem in your garden:

• Use raised beds.
• Avoid overhead watering.
• Space plants in such a way as to provide good airflow.
• Apply only as much nitrogen as is needed.
• Inspect senescent flowers and leaves for signs of infection.
• Remove and dispose of infected plants immediately.
• Monitor plants closely after 60°F to 70°F days with high relative humidity (95–100%).
• Inspect nearby ornamental plants and weeds for signs of infection.
• Employ crop rotation with non-host plants.

Severe infestations may require fungicides or soil solarization.

As prevalent as white mold is, it’s a good idea to know what to look for ahead of time.