Crown Rot

Crown rot is decay of the plant tissue at the crown - the transition zone between stem and root system at or just below the soil surface. The crown is vulnerable because it sits at the interface of above-ground and below-ground environments: persistently moist soil from below, warm air-mediated fungal spores from above. Multiple soilborne pathogens exploit this vulnerable zone.

Causal Organisms

Sclerotinia sclerotiorum (white mold / stem rot): Produces water-soaked lesions at the crown and lower stem, followed by white cottony mycelium and hard black sclerotia (resting bodies that persist in soil for years). Attacks a broad range of crops including tomato, carrot, celery, brassicas, lettuce, beans, and many others. Cool (50-70°F), wet conditions favor infection.

Phytophthora crown rot (Phytophthora spp.): Water molds that cause rapid crown and root decay in waterlogged or poorly drained soils. Common in tomatoes, peppers, squash, and fruit crops during wet periods. Brown to black lesion at the crown; plant wilts and collapses rapidly.

Rhizoctonia solani: Causes damping-off in seedlings and crown canker/stem rot in older plants. Brown to reddish-brown lesion at or below the soil line. Common in warm soils.

Botrytis cinerea (gray mold): Favors cool, humid conditions. Gray fuzzy sporulation on affected crown tissue. More common in greenhouse settings and in plants with injuries or frost damage that create entry points.

Strawberry Crown Rot

Strawberries are particularly vulnerable to crown rot because the crown is the entire structure of the plant - there’s no secondary stem below ground. Phytophthora fragariae (red stele) and Botrytis cinerea are the most common causes, but Rhizoctonia and Pythium also contribute.

Symptoms: plants wilt suddenly in warm weather despite adequate water; the crown, when cut lengthwise, shows brown discoloration in the central cylinder. Compare to a healthy crown’s white to cream interior.

Prevention for strawberries: Plant in well-drained sites or raised beds; avoid crown burial at planting (the crown should be exactly at soil level, not buried); remove and destroy infected plants and surrounding soil; rotate strawberries to new beds every 3-4 years.

Prevention and Management

Drainage is the primary management variable. Crown rot pathogens require moisture at the soil surface. Raised beds and well-amended, well-draining soils dramatically reduce incidence.

Mulch placement. Pull mulch 2-3 inches back from plant crowns and stems. Mulch in direct contact with stems keeps the crown area persistently moist. The wood chip berm around tree trunks (“mulch volcanoes”) commonly seen in landscaping is a classic crown rot initiator.

Planting depth. Most crown rot problems in transplanted crops are worsened by planting too deep, which buries stem tissue that isn’t adapted to soil moisture. Tomatoes can be planted deep (they root from buried stems); peppers, squash, and most other crops should not be planted with the crown below soil level.

Biological fungicides. Trichoderma harzianum and Bacillus subtilis products applied at transplanting can colonize root zone and crown area, competing with pathogenic fungi. Efficacy is preventive; they don’t reverse established infections.

Remove infected plants. Once crown rot is established in a plant, remove and dispose of it (don’t compost) to prevent spread of sclerotia and spores to neighboring plants.