Botrytis Crown Rot

Symptoms include a water-soaked, brownish-gray to brownish-orange, soft wet rot that occurs on the oldest leaves in contact with the soil. These old leaves are often damaged or senescent and are therefore particularly susceptible. From these leaves, the pathogen moves into the healthy parts of the lettuce plant and causes a decay of the crown. A characteristic fuzzy gray to brown growth covers diseased areas, especially basal leaf and crown tissue that is shaded and protected from drying by overlying foliage (which is why the disease is also called gray mold).

Flat, black sclerotia may form on infected tissues. In advanced stages of the disease, lettuce crowns can become completely rotted and entire plants will wilt and collapse. The wilting and collapsing symptoms are somewhat similar to lettuce drop and phoma basal rot. Romaine cultivars appear to be especially susceptible.

Transplanted lettuce can become infected where the stem is in contact with soil; such infections can cause the plant to be delayed in development or to collapse. Botrytis crown rot on young plants can therefore result in significant stand reduction.

Botrytis crown rot is usually a minor disease of lettuce but can cause significant damage if field conditions are favorable for the pathogen. The risk of Botrytis crown rot damage increases with plant injury and cool, wet conditions.

To prevent botrytis crown rot:

• Limit damage caused by farming practices, environmental extremes, or other pathogens and pests.
• Avoid extensive and prolonged wetting of the bed tops to help lower disease severity.
• Use lettuce transplants that are not overgrown; old transplants are subject to additional leaf breakage and damage during planting, and hence are more susceptible to infection by B. cinerea.

Reduce crown rot problems by applying protectant fungicides after thinning.

• Apply a fungicide before plants become too large.
• Direct applications to the base of the young plants.