Brown Spot
A lug of Virginia Bright Leaf with Brown Spot.
Brown Spot is a fungal disease that causes brown spots, composed of characteristic concentric rings. Alternaria alternata, the causative fungus, is also responsible for "Early Blight" in tomatoes, typically causing lower branches on the tomato vine to turn brown and die.
The individual lesions can range in size from a tiny dot to several inches across.
On tobacco leaf, each area of the lamina affected by the fungal infection develops a hard, circular blemish, surrounded by early yellowing and eventual necrosis. It typically affects lower leaves, then slowly spreads to upper leaves. In damp shed conditions, the lesion may continue to grow, but is not likely to infect other leaves there. In the field, however, ideal conditions for growth of Brown Spot are a temperature of 85ºF and high humidity. A long stretch of rainy days in mid-to-late season, together with high temperatures are the highest risk times. During dry conditions, the fungus is able to spread from earlier lesions to other plants. Closer plant spacing also encourages spread.
The fungus dwells in the soil, so crop rotation is helpful (but must be to a crop unrelated to tobacco). Earlier priming or earlier stalk harvesting limits continued spread on that plant.
A limited Brown Spot infection simply results in some dead spots on some of the leaf. The spots often fall out during kilning or flue-curing, and the leaf can be smoked safely.
I found that the cigar variety Jalapa is very susceptible to Brown Spot, causing fairly large lesions that affected most of the leaves of entire plants. For this reason, and since I frequently see early blight in my tomatoes--suggesting that the organism is common in my soil, I no longer grow Jalapa.
Bob
A lug of Virginia Bright Leaf with Brown Spot.
Brown Spot is a fungal disease that causes brown spots, composed of characteristic concentric rings. Alternaria alternata, the causative fungus, is also responsible for "Early Blight" in tomatoes, typically causing lower branches on the tomato vine to turn brown and die.
The individual lesions can range in size from a tiny dot to several inches across.
On tobacco leaf, each area of the lamina affected by the fungal infection develops a hard, circular blemish, surrounded by early yellowing and eventual necrosis. It typically affects lower leaves, then slowly spreads to upper leaves. In damp shed conditions, the lesion may continue to grow, but is not likely to infect other leaves there. In the field, however, ideal conditions for growth of Brown Spot are a temperature of 85ºF and high humidity. A long stretch of rainy days in mid-to-late season, together with high temperatures are the highest risk times. During dry conditions, the fungus is able to spread from earlier lesions to other plants. Closer plant spacing also encourages spread.
The fungus dwells in the soil, so crop rotation is helpful (but must be to a crop unrelated to tobacco). Earlier priming or earlier stalk harvesting limits continued spread on that plant.
Univ. Georgia Ag. Extension Service said:Brown spot, caused by Alternaria alternata, is a foliar disease that usually develops from mid season to
harvest. It begins in the lower leaves and works up the plant. Brown spot is favored by wet weather, excess
nitrogen and tight plant spacing. Fungicides are not effective for brown spot control.
http://caes2.caes.uga.edu/commoditi.../documents2013/8TobaccoDiseaseControl2013.pdf
A limited Brown Spot infection simply results in some dead spots on some of the leaf. The spots often fall out during kilning or flue-curing, and the leaf can be smoked safely.
I found that the cigar variety Jalapa is very susceptible to Brown Spot, causing fairly large lesions that affected most of the leaves of entire plants. For this reason, and since I frequently see early blight in my tomatoes--suggesting that the organism is common in my soil, I no longer grow Jalapa.
Bob