Lettuce: Bottom rot

• Categories: Lettuce Lettuce Diseases Vegetables
• Last review date: 2026-07-31 12:47

Biology

Bottom rot of lettuce is caused by a soil-borne fungus that is common in wet soils. Head lettuces, particularly the ‘Big Boston’ types, are attacked as they near maturity.

The stems and midrib/midvein of lower leaves develop sunken, brown, necrotic spots which may enlarge to involve the entire stem or midrib. The surface of the spots may show a brown exudate or may be covered with a white to brown growth of the fungus. Brown or gray-brown fruiting bodies of the fungus can also be present in the lesions.

Infected heads become slimy and later dry into a blackened mummy. Bacterial rots often attack lettuce after infection by bottom rot.

The fungus causing bottom rot of lettuce also commonly causes damping-off of seedlings and seed rots in many species of plants.

Management Options

See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.

Non-chemical Management

Select non-chemical management options as your first choice!

• Rotate crops. Do not plant lettuce in the same location each year.
• Plant non-susceptible crops such as sweet corn and onions in infected areas.
• Plant in well-drained soils or raised beds.
• Space plantings to provide good air circulation.
• Do not overwater.

Chemical Management

IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides, visit Home and Garden Fact Sheets | Pesticide Resources and Education Program | Washington State University. Also visit Pacific Northwest Pest Management Handbooks.

• None recommended.