HPIPM:Potato Early Blight

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Subclass	Pleosporomycetidae
Order	Pleosporales
Family	Pleosporaceae
Genus	Alternaria

Scientific Name

Alternaria solani

Scientific Name Synonyms

Alternaria allii

Common Name

early blight

Author: Howard F. Schwartz, David H. Gent, and Gary D. Franc

Identification and Life Cycle

Potato early blight is caused by the fungus Alternaria solani and occurs wherever potatoes are grown, and is the disease most targeted by potato growers with fungicides in the U.S. The pathogen can infect both foliage and tubers. Infection occurs when spores (conidia) land on leaves, germinate in the presence of free moisture or high relative humidity, and infect the plant by direct penetration. As lesions develop and produce spores they become a source of secondary spread of the fungus to other leaves and plants. Sporulation can occur over a range of temperatures (41 to 86ºF), but most spores are produced near 68ºF when alternating wetting and drying of foliage occurs. Spores are readily moved by wind. Tuber infections occur when contaminated soil and spores come into contact with wounds made during harvest. The fungus can survive between potato crops in and on other hosts such as tomato, volunteer and cull potato, soil, and crop debris.

Plant Response and Damage

Initially potato foliage appears as dark spots with concentric rings of alternating raised and depressed dead (necrotic) tissue. Lesions are initially circular with or without a yellow border, but later become angular and irregularly shaped as they encounter veins. As the disease progresses, necrotic lesions form on stems and petioles. Severely infected leaves may become entirely necrotic, but remain attached to plants. Lesions first appear on lower, older leaves of older plants.

Tuber lesions appear as circular to irregularly-shaped dark, sunken areas often with a raised margin. Lesions have a leathery or corky appearance with yellow to greenish yellow water-soaked margins.

Yield losses associated with early blight typically approach 20% if left untreated in the High Plains, but are generally less than 5% if treated with fungicides. Tuber infections reduce seed quality, marketability, and processing value and are often as important as foliar infections in the High Plains.

Biological Control

No biological control practices have been developed for potato early blight.

Cultural Control

Early blight is most severe when plants are stressed by other diseases, insects, or environmental conditions. Plant only high quality seed free from other pathogens. Provide adequate but not excessive irrigation and fertility for optimal crop development. Varieties differ widely in their susceptibility to early blight; highly susceptible early maturing varieties such as Russet Norkotah should be avoided if possible. Practice a 2 to 3 year crop rotation with non-susceptible hosts. Harvest at least 14 days after vine kill to ensure tubers have complete skin set which will reduce skinning injury and storage losses. Adjust equipment to reduce tuber bruising and injury during harvest and handling. Store in an environment that promotes rapid suberization and wound healing immediately after harvest.

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.