HPIPM:Cottony Rot (White Mold)

Author: Howard F. Schwartz and David H. Gent

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Leotiomycetes
Subclass	Leotiomycetidae
Order	Helotiales
Family	Sclerotiniaceae
Genus	Sclerotinia

Scientific Name

Sclerotinia sclerotiorum

Scientific Name Synonyms

Sclerotium varium

Sclerotinia libertiana

Sclerotium opuntiarum

Sclerotinia sclerotiorus

Common Name

Sclerotinia timber rot

Identification and Life Cycle

Cottony rot is caused by the fungus Sclerotinia sclerotiorum. Infection by S. sclerotiorum occurs when sclerotia (dormant resting structures) germinate when the soil surface is continuously wet for at least two weeks. The germinating sclerotia form small, tan, cup-shaped structures called apothecia, which release millions of airborne ascospores that infect carrot. Sclerotia can survive in soil up 8 to 10 years. White mold affects many plants and crops, including lettuce, sunflower, bean, and potato, among over 400 other plant species.

Plant Response and Damage

Initial symptoms appear as small, water-soaked, lesions on crowns and roots. A snowy white mycelium and black, irregularly shaped sclerotia become apparent as disease progresses. Disease losses vary depending on cropping history and weather conditions, but disease losses as great as 70% are not uncommon.

Biological Control

Contans is a commercial formulation of a fungus pathogenic to S. sclerotium sclerotia, and may reduce white mold incidence and/or severity when applied to soil for many years.

Cultural Control

Avoid excessive irrigation and fertilization that leads to dense, lush canopies favorable for white mold. Promote air movement within the canopy by planting cultivars with smaller, upright architecture, planting rows parallel to prevailing wind direction, and planting on wider row spacing. These practices will reduce the duration of leaf and soil wetness, and may help reduce white mold in semi-arid production areas. If possible, use drip irrigation or schedule irrigations to prevent continuous leaf and soil wetness. Deeply incorporate crop debris to bury sclerotia.

Chemical Control

Chemical controls are most effective when combined with cultural control strategies and are generally not necessary if sound cultural practices are followed.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.