by David "Doc" Diaz
Monday March 24, 2008
While tobacco is a plant whose growth is prolific, it is also susceptible to various diseases that can reduce the yield, at best, or devastate the crop, at worst. Whether caused by a fungus, bacteria, or virus, any abnormal conditions are treated as a contagious disease. Farm workers are instructed not to touch plants that present with any type of leaf damage. Since pathogenic spores can easily be transferred between plants, the plants must be quarantined and the contagion eliminated. Special teams of workers will swarm the tobacco fields like a hazmat crew in a hot zone. They will carefully bag the infected plants and take them to a remote location for destruction.
Below: Blue Mold infected tobacco leaf must be quarantined and destroyed
A common foe of tobacco is Blue Mold [source: Burley and flue-cured tobacco: Blue mold], which is caused by a fungus. In 1957 blue mold was first reported in Cuba. In 1960 a blue mold epidemic spread on tobacco in about 11 countries in Central Europe and losses were estimated at $25 million. The first report of blue mold in Mexico was in 1964.
Young seedlings, up to 4-weeks old, are very susceptible to blue mold and are easily killed by the fungus. Leaves of older seedlings are puckered and deformed and dark, dead areas may develop. Infection with blue mold in the field usually starts on the lower leaves. Yellowish round spots develop on the upper surface of the leaf with corresponding purplish to grayish mold on the lower surface. Under severe conditions the spots expand forming dark areas. Often the fungus penetrates the midrib and/or the veins of the leaves and reaches the vascular tissue of the stem causing wilting. Such infection of the vascular tissue of the plant is known as "systemic infection". Systemic infection of young plants causes severe stunting and wilting and leaves become narrow and short with clear mottling. The vascular tissue of such plants turns brown and the weakened stalk may cause the plants to topple over. The fungus is airborne and thus can spread easily to adjacent plants.
Below: Stalk damage of Black Shank disease
Black Shank [source: Black Shank], another common enemy of tobacco, typically infects the roots of tobacco plants. It is caused by the fungus Phytophthora parasitica var. nicotiana, which lives in the soil. This pathogen belongs to a group of fungi that occurs commonly in areas of high soil moisture. The fungus produces microscopic spores which swim in water surrounding roots and/or soil particles. These swimming spores are attracted to tobacco, their only natural host, by substances exuded in the roots of the tobacco plants. Black shank is a warm-weather disease, which is favored by temperatures ranging from about 84 to 90 F. Once soil in a field becomes infested with the black shank fungus, it cannot be eliminated, therefore, the disease must be managed every year on a continuing basis.
The disease is characterized by a rapid yellowing and wilting followed by death of the entire plant. A dark brown to black, somewhat sunken, lesion usually appears on the stalk at or near the ground level. This lesion often extends up the stalk or shank of the plant causing it to turn black.
There are several other diseases that affect tobacco plants, including Mosaic Virus, which is known to infect members of nine plant families, and at least 125 individual species, including tobacco, tomato, pepper (all members of the useful Solanaceae), cucumbers, and a number of ornamental flowers.
About the Author
David "Doc" Diaz is the publisher and the editor of the Stogie Fresh Cigar Publications. He has served as an educator, researcher and writer and has taught in the Health Education and Health Science field for over 30 years. He possesses an earned doctorate from Nova Southeastern University. Doc is a Certified Master Tobacconist (CMT), having received this certification from the Tobacconist University and is a member and Ambassador of Cigar Rights of America (CRA).blog comments powered by Disqus