Target spot is endemic to South Carolina tobacco fields and is caused by a fungus (Thanatephorus cucumeris). Disease development is more severe during wet weather. Little target spot occurred in South Carolina during 2008. The symptoms appear similar to brown spot and are easy to confuse. Necrotic tissue can become brittle, fall out, and leave a shot hole appearance. Under high relative humidity lesions can increase rapidly blighting large portions of the leaf. Quadris fungicide received a label for control of target spot in 2006. Please check the Quadris label for application directions prior to use.
Brown spot is a disease of the maturing leaves of tobacco and is most serious during periods of high humidity. The best measures to reduce losses to brown spot are to plant varieties tolerant to the disease, avoid excess nitrogen fertilization which delays maturity, and alter spacing of plants in the row to increase air circulation and reduce humidity. Be aware of conditions favorable for infection by the brown spot fungus. If such conditions occur during harvest, increasing the priming rate should help to stay ahead of the disease. Fungicide control is not successful and is therefore not recommended.
Blue mold was not observed in South Carolina during 2008. Blue mold occurs in Florida and Georgia almost every year and has the potential to cause severe losses in South Carolina. Ridomil resistant strains have been observed in other states and pose a possible threat to the tobacco crop in South Carolina. Blue mold is potentially one of the most destructive diseases of tobacco. It is caused by a fungus (Peronospora tabacina) that is airborne, and disease can spread very quickly, leading to epidemics, if not properly managed. This occurred in 1979 and 1980 in all tobacco-producing states, leading to tremendous losses. Ridomil has generally given good control of blue mold when used as a preplant soil incorporation treatment. However, if a Ridomil G insensitive strain occurs in South Carolina other control options should be considered. Acrobat has received a label for blue mold control but should be used in combination with another fungicide. Actigard 50 WG received a label for blue mold control in 2000.