Image Number: 1402025

This fungal disease appears first on the older leaves as circular, brown spots (1/4 to 1 1/4 inches in diameter) with sharply defined margins. Concentric circles (rings) are often noticeable within the spots. As the leaves approach maturity, a yellowish "halo" of varying width often forms around the lesion. Lesions may merge, forming large areas of dead tissue. During humid weather, sporulation of the fungus may be abundant, giving the lesions a black, dusty appearance. Brown spot is most severe as the plant approaches maturity, and the disease progresses from the lower to the upper leaves. Disease severity depends much on the weather, the overall health of the plant, varietal tolerance, and harvest rate.
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Kingdom: Fungi
Phylum: Ascomycota
Subphylum: Pezizomycotina
Class: Dothideomycetes
Subclass: Dothideomycetidae
Order: Pleosporales
Family: Pleosporaceae
Genus: Alternaria
Subject: Alternaria alternata (Fr.) Keissl.


Kingdom: Plantae
Phylum: Magnoliophyta
Class: Magnoliopsida
Subclass: Asteridae
Order: Solanales
Family: Solanaceae
Genus: Nicotiana
Subject: Nicotiana tabacum (flue-cured type) L.
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Image uploaded:
Sunday, March 10, 2002
Image last updated:
Tuesday, May 17, 2011