What's Attacking My Tobacco?

Diseases and nematodes come in a number of combinations. The major diseases that attack tobacco in the United States are Granville wilt and black shank, while the major nematodes include southern root-knot and tobacco-cyst nematodes. Nematodes often cause the initial injury to roots that provides an entry point for bacterial and fungal diseases.

• Granville wilt, a bacterial disease, often makes its way into the root system of tobacco plants through entry points opened by nematodes. It causes the most damage in wet areas, in fields where tobacco was previously grown and in years when soil temperatures are normal or higher. Symptoms of Granville wilt include wilting that can lead to death, stunting, distorted leaves and a black stalk. These symptoms can be seen several weeks after the initial infection.

• Black shank, a fungal disease, is one of the most prevalent and damaging tobacco diseases. It is a warm-weather disease that can be found primarily in poorly drained locations where tobacco was previously grown. Symptoms include rapid yellowing and wilting, a dark-colored lesion at the base of the stalk, and decayed roots and crowns. Black shank is spread when infested soil is moved from one area to another.

• Southern root-knot nematodes are named for the galls they create on plant roots that look like knots in a rope. These nematodes are the world's most damaging nematode in tobacco. It causes the most economic damage of any nematode, due to its widespread distribution. They can be found in nearly any field, but are most commonly found in sandy soils. The incidence of other diseases increases significantly when these nematodes attack.

• Tobacco-cyst nematodes are nematodes that continue to spread to new fields, farms and counties within Virginia, North Carolina and Maryland. The economic impact of cyst nematodes is twofold. Not only can the pests cut tobacco yields in half by severely retarding the plant growth, but cyst nematodes also weaken plant immune systems and create entry sites for secondary diseases, such as black shank and Granville wilt.