Even though it seems like Tomato Spotted Wilt Virus has hit tobacco growers hard in some areas this season, traditionally, severity of plant loss is due to Black Shank, which has recently been noticed in fields.
Black Shank is caused by a fungal-like organism that lives in high moisture soil climates. Tobacco plants that have been infected via the plants root system, exhibit symptoms of yellowing and wilting of leaves, brown to black lesions on the stalk near soil line, and if cut into the pith of the stalk often appears dark and dry creating a disking appearance.
Due to not having complete resistant flue-cured tobacco varieties, growers have to take steps in attempt to lessen the severity of the disease. First and foremost, crop rotation is very important. A four-year rotation is best, however that doesn’t always fit all farms. The lesser the crop rotation time frame with tobacco increases the chances of disease if conditions are favorable. Field history plays a role in various crop rotation plans.
Bedding and fumigating tobacco land with a history of high disease pressure is beneficial. Bedding tobacco rows creates a raised area for the plant roots to grow while making efforts to minimize water standing in the row around the base of plants, as I had mentioned earlier about this disease thriving on high moisture levels in soils.
In addition to bedding and fumigating, tobacco growers apply protective fungicide products during several stages: transplant, first cultivation, and layby. The fungicides used during these growth stages are rotated in efforts to minimize any resistance development to the products being used. These are soil applied products, so in other words, they are applied to the soil and incorporated into the soil near the root zone of the plant, which is the entry point for the fungal-like organisms.
Even though tobacco growers make every effort to protect their crops, diseases such as black shank can still make an appearance if conditions are favorable. Unfortunately, there are no complete resistant varieties in the industry, however, some varieties do have some traits of resistance to either the Race 0 or Race 1 of the black shank disease.
Della King is an Extension Agent with the Sampson County Cooperative Center specializing in Field Crops. She can reached by phone 910-592-7161.