Sclerotinia Rot

Sclerotinia spp.

Sclerotinia Rot is the broad library identity for soft rots caused by members of Sclerotinia when the affected organ or production system is not adequately represented by the narrower Sclerotinia Stem Rot or White Mold articles. Susceptible material includes fleshy vegetables, storage organs, crowns, petioles, flowers, and ornamentals. The operational signature is a soft or water-soaked rot that may become covered by dense white cottony mycelium and later develop hard black sclerotia. Sclerotia may be irregular, rounded, or elongated and can form inside hollow stems or within decayed tissue. Botrytis, Rhizopus, bacterial soft rot, southern blight, and noninfectious storage breakdown can resemble parts of the syndrome. Because Sclerotinia species differ in host range, infection courts, and production importance, this umbrella record should support triage and sampling rather than an automatic species diagnosis. In North Florida, episodes are most plausible during cool, persistently wet periods, in protected production, or where infected transplants and contaminated soil introduce resting bodies.

Identification

Classify this record as a pathogen-complex umbrella, not as a synonym for every occurrence of white fungal growth. Confirm the host, organ, field or storage setting, temperature history, and whether the rot began at flowers, wounds, the soil line, or points of contact. Look for firm black sclerotia embedded in or attached to diseased tissue; these structures are more diagnostic than white mycelium alone. Collect an intact transition from healthy to recently softened tissue, any sclerotia, and a separate healthy comparison. Avoid submitting only liquefied centers because secondary bacteria and saprophytes rapidly dominate them. A laboratory may induce sporulation, examine sclerotial and ascospore characters, culture the fungus, or use molecular assays. Visual examination generally cannot distinguish S. sclerotiorum from related species or prove that an isolate recovered from old decay initiated the problem. Keep this article distinct from Sclerotinia Stem Rot, which centers on stem-node and flowering-associated disease, and from White Mold, which is the common-name crop syndrome centered on S. sclerotiorum.

Symptoms / Signs

Initial lesions are pale, water-soaked, or slightly sunken and may expand with little odor. In humid conditions the surface develops white, cottony mycelium that bridges nearby tissues. Black sclerotia then form on the surface, within stems, or among collapsed plant material. Leaves and shoots above crown or stem infections wilt while remaining green, then bleach or turn brown. Storage organs can become soft and wet but may retain a relatively firm advancing margin. Bacterial soft rot usually produces stronger odor and more complete maceration; Rhizopus commonly forms coarse aerial growth with dark sporangia; southern blight produces many small tan-to-brown mustard-seed sclerotia concentrated near warm soil surfaces. Absence of visible sclerotia does not exclude an early Sclerotinia infection.

Life Cycle / Process

Sclerotinia fungi persist primarily as sclerotia in soil, crop debris, stored material, or contaminated lots. Depending on species and conditions, sclerotia may germinate directly by producing mycelium or indirectly by producing apothecia that release airborne ascospores. Ascospores often require nutrient-rich senescent tissue, damaged flowers, or wounds before invasion of healthy organs. Cool to moderate temperatures, high humidity, prolonged wetness, and dense canopies favor colonization. Sclerotia can survive for years and move with soil, transplants, equipment, cull material, irrigation runoff, or contaminated seed lots. A visible rot may therefore arise from local resting bodies, airborne inoculum, or infected planting material; the likely route must be inferred from the crop and distribution rather than assumed from the common name.

Prevention

Use clean propagation material and reject plants, bulbs, or produce bearing unexplained soft rot or sclerotia. Prevent persistent canopy wetness with adequate spacing, ventilation, timely irrigation, and drainage. Remove culls and crop debris rather than incorporating heavily infested material into beds used for susceptible crops. Clean soil from tools, carts, footwear, and containers before moving between production zones. Rotate away from susceptible broadleaf hosts when practical, recognizing that the broad host range and longevity of sclerotia limit short rotations. In storage, cool commodities promptly, prevent condensation, minimize wounds, and segregate suspect lots. Do not depend on a generic fungicide program: effective timing and labeled uses vary sharply among flower infections, crown rots, field vegetables, ornamentals, and stored crops.

Management / Control

Isolate the affected lot and stop movement of soil or decayed material. Confirm whether the finding belongs in this umbrella record or should be reassigned to the stem-focused or White Mold article. Remove severely diseased tissue and visible sclerotia in a way that prevents them from dropping into clean beds; bag or otherwise contain material according to site disposal rules. Correct prolonged wetness, condensation, overly dense canopy, or irrigation practices that maintain contact moisture. For high-value crops, submit fresh advancing lesions before making a treatment decision. Where a crop-specific fungicide or biological product is considered, verify the host, disease, application site, resistance-management group, preharvest interval, and state label. Postinfection sprays rarely restore rotted organs. Document the location because recurrence from sclerotia may appear in the same beds or handling areas in later cycles.

Procedure Steps

1. Mark the affected lot and photograph the whole-plant or storage pattern before disturbance. 2. Record the host, organ, crop stage, recent temperature and wetness, irrigation method, and whether flowers or wounds preceded symptoms. 3. Inspect the advancing edge for white mycelium and collect every black resting body found without crushing it. 4. Package firm lesion margins and sclerotia in dry paper or a ventilated diagnostic container; place leaking tissue in a secondary sealed bag, not in direct contact with healthy samples. 5. Compare the lesion with bacterial soft rot, Rhizopus, Botrytis, southern blight, and chilling or storage injury. 6. Contain culls and sanitize surfaces after removing organic matter. 7. Submit the sample when species identity, crop movement, repeated losses, or pesticide selection depends on confirmation.

Safety Notes

Decayed vegetables and storage organs should not be sold or consumed when identity, secondary contamination, or food quality is uncertain. Wear gloves and eye protection when handling wet decay, disinfectants, or fungicides, and wash hands before food handling. Never mix disinfectants unless the product directions explicitly allow it. Keep removed sclerotia and infested soil out of compost intended for susceptible production. Follow the entire pesticide label; a product registered for one Sclerotinia disease, crop, or application site is not automatically legal or effective for another.