Large dead areas develop in the leaf lamina. This is one of the most destructive phases of tobacco mosaic infection. Mosaic infected leaves may be mildly distorted. As the leaves approach maturity, a yellowish halo of varying width often forms around the lesions. The rate and amount of spread depends on the weather, the overall health of the plant, varietal tolerance, and harvest rate.
Yellowish halos form around brown spot lesions on mature leaves.
Lesions may merge, forming large areas of dead leaf tissue. Blue Mold Blue mold can occur in the plant bed or field. Spots become light brown when the leaf tissue dies. The disease first develops on lower leaves. It rapidly spreads to upper leaves during wet, cool weather.