HPIPM:Potato White Mold

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

Author: Howard F. Schwartz and David H. Gent

Identification and Life Cycle

White mold is caused by the fungus Sclerotinia sclerotium. The pathogen has a very broad host range, attacking over 400 plant species including dry bean, carrot, lettuce, melons, sunflower, and several weeds. The fungus produces a dormant resting structures called sclerotia that can survive for 3 to 5 years in the soil. These sclerotia may germinate under cool, moist conditions and directly infect stems and leaves in contact with the soil, or produce a mushroom like structure called an apothecium. Apothecia release up to 8 million windblown ascospores that are spread within the field. The ascospores land on and colonize senescing tissues such as flowers and leaves, and later invade healthy tissues. New sclerotia are formed on the diseased tissues and are returned to the soil.

Plant Response and Damage

White mold symptoms initially appear as soft, watery lesions on stems on or near the soil, but become bleached or tan when dry. Under wet, humid conditions lesions can expand and girdle stems, causing wilting of foliage above the lesion. White, fuzzy growth and black sclerotia are generally apparent on lesions. Tuber infections are rare, but have been observed. Lesions are initially small and depressed near eyes, but enlarge, become blackened, and cause a soft rot. Infected tubers are often filled with fungal mycelium and sclerotia. Yield losses from white mold are difficult to assess in potato, but probably cause little loss even when disease is severe.

Biological Control

Contans is a commercial formulation of a fungus pathogenic to S. sclerotium sclerotia, and may reduce white mold incidence and/or severity with repeated applications over several 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, schedule irrigations to prevent continuous leaf wetness throughout the evening.

Chemical Control

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.