HPIPM:Alternaria Leaf Spot CC

Author: Howard F. Schwartz and David H. Gent

Taxonomy

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

Scientific Name

Alternaria brassicicola

Scientific Name Synonyms

Alternaria circinans

Alternaria oleracea

Common Name

black spot

Identification and Life Cycle

Alternaria leaf spot is caused by the fungus Alternaria brassicicola, and is generally only a problem on cabbage and Chinese cabbage during extended cool, rainy weather. Broccoli and cauliflower are rarely infected by this pathogen. Infection occurs when windblown spores land on leaves and infect through natural openings, wounds, or directly penetrate the leaf. Lesions on diseased plants release abundant spores during dry periods, and alternating cycles of evening leaf wetness followed by daytime drying favor disease and sporulation. The pathogen survives between susceptible hosts in crop debris and on seed.

Plant Response and Damage

Alternaria leaf spot lesions first appear as small, dark areas that develop into large, circular lesions with concentric rings that resemble a bull’s-eye pattern. A lesion appears dark brown when wet, but when dry the lesion appears velvety. The disease reduces the photosynthetic area of infected plants, but may also cause lesions on brussel sprouts.

Biological Control

No biological control strategies have been developed for Alternaria leaf spot.

Cultural Control

Plant only high quality seed free from the Alternaria leaf spot pathogen. Practice a three-year or longer rotation to non-hosts. Deeply incorporate crop residues after harvest to reduce pathogen survival. Avoid overhead irrigation where possible. Promote air movement in the canopy by planting wide rows parallel to the prevailing wind direction. If possible, irrigate so that the canopy dries before dusk to prevent extended periods of leaf wetness.

Chemical Control

Fungicides are most effective when used in combination with cultural control strategies.

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.