Living with Black Shank - Second Quarter 2009
"The" disease for tobacco farmers.
TFQ Editorial Staff
In 1956, NC State’s College of Agriculture & Life Sciences published its first annual Tobacco Abstracts, a synopsis and index available to the public that focused on innovations, trends and journal articles that were of interest to tobacco growers. In that first issue, black shank disease was discussed at length, as it has been in each and every issue since. Now, here we are 53 years later and black shank is still an important topic to tobacco growers, so it’s probably safe to say this wretched disease isn’t going away any time soon.
“Whenever I go speak to groups around the state, they may ask that I also talk about some different diseases that are more specific to the region, but they know the one I’m definitely going to talk about is black shank,” says Dr. Asimina Mila, a plant pathology expert at NCSU who specializes in tobacco. “There’s no way to completely eliminate it, but you can take steps to reduce the chances of it affecting your yield. With proper planning, even if it does show up in your field, a good manager can find a way to limit it.”
As with all soil-related diseases impacting tobacco, the most effective way to prevent black shank is through proper rotation.
“North Carolina’s piedmont region has the most serious problems with black shank because they have limited land resources, and so they often have to go with shorter rotations,” says Dr. Mila. “The longer you can rotate the better it will be. A three-year rotation is better than two; four is better than three. There’s no ‘gold standard’ for rotation, but the longer you can go the better it is for the grower.”
The variety of seed used also will have a large impact. Resistant varieties have worked well to control most races over the years, but black shank has developed a resistance to those varieties and developed a new race—race 1—that most resistant varieties are not immune to.
“If growers used the resistant varieties extensively, they are most likely going to have some of this new race in their fields,” Dr. Mila says. “And that means they cannot rely on the resistant varieties to control it anymore. If you use resistant varieties over and over, you are going to have race 1 appear. And if you’re not using proper chemical control, don’t be surprised if the field collapses.
“I’ve been in fields where they had a few plants dying because of black shank, and they thought maybe they could go back one more time and be OK. And there have been several times—where it seemed like overnight—that it goes quickly from a low percentage to total collapse. It’s very shocking.
“We have a few varieties of seed that are resistant to any kind of race, but I still insist that they need to use chemical control, because that’s all we really have.”
According to the North Carolina Cooperative Extension Service, several soil-applied chemicals are labeled for black shank control; however, systemic fungicides Ridomil Gold or Ultra Flourish (not to be used with highly susceptible burley or black varieties) are the most effective materials against black shank. The problem with the fungicides, however, is that they are not inexpensive and will raise production costs.
“Growers need to monitor their diseases, because the diseases in tobacco really do cost money,” says Dr. Mila. “If they spend their money well, they shouldn’t look at it as an expense. They should look at it as an investment that is going to pay back in the end.
“I recommend using chemicals at the first cultivation, and if everything is done well, that should assist a significant amount. But once you see plants going down with blank shank, that means there are many more plants already infected and it’s just a matter of time. Adding another treatment is better than nothing, but because it needs to be incorporated in the soil, the final cultivation is the last shot we have.”
As always, it is up to the individual grower to draw on personal experience and combine that with the information provided by researchers and Extension agents to determine what combination of options will produce the best overall crop.
“At the end of the day, growing tobacco is a business and with that comes risk,” Dr. Mila says. “How much money you make depends on what kind of manager you are. With each variety you know the potential yield and the potential resistance to disease going in. You know how fields have performed in the past: Is it a good field with high potential for a good yield? What kind of history does it have with disease? How long was the rotation? All these questions have to be factored in.
“All these are complicated decisions, and at the end of the day you need to do what’s going to bring the most money to the bottom line.”
Even if that requires overcoming a little black shank.