What is in this article?:
- Better black shank fungicide battle plans for burley tobacco growers
- Know the label; know the law
- Though many tobacco varieties now are resistant to black shank, improved management still needs proper fungicide choices and application.
BLACK SHANK, symptoms seen here in a hard-hit area of a Kentucky burley field, remains burley tobacco growers’ No. 1 disease enemy. Varieties are resistant to it, but choosing the right fungicides and applying them in the right ways can make the difference in losing a crop or securing yields.
Black shank is the most serious disease faced by burley tobacco growers. Many varieties now available have very good to excellent resistance to it. Fungicides on the market for control of black shank do a good job, too, but need to be applied correctly to get best results and investment return.
The number of fungicides out there for black shank in tobacco is pretty small: Ridomil Gold SL, Ultra Flourish, and MetaStar 2E AG.
Ridomil Gold and Ultra Flourish contain the active ingredient mefenoxam, while MetaStar contains metalaxyl and is similar to the original Ridomil 2E that was introduced back in the 1980’s. Mefenoxam is a purified form of metalaxyl, meaning that Ridomil Gold, Ultra Flourish, and MetaStar all work the same way against the black shank pathogen (called Phytophthora nicotianae). These products perform similarly against black shank as long as they are used correctly. Each fungicide is formulated differently. The actual rate of the product per acre will be different.
Ridomil Gold is the brand-name product and the cost per acre for a treatment is over $100 (based on a 1 pt/A application), while Ultra Flourish and MetaStar are often less expensive. If choosing to use either Ultra Flourish or MetaStar, keep in mind that the use rates are higher because these products are less concentrated. When comparing prices between these two products and Ridomil Gold, figure out the actual cost per acre based on the planned use rate; don’t focus on the price of the container.
Fungicides usually give the best results against black shank when they are applied to resistant varieties (4 or better on the rating scale for race 0 and race 1) planted on properly rotated ground. Ridomil Gold (as well as Ultra Flourish and MetaStar) will not provide acceptable control on varieties with little or no resistance planted in locations that have a history of moderate-to-severe black shank. Good soil moisture is needed when these fungicides are applied so that enough material is taken up by plant roots.
Where black shank has been a problem in the past, consider making a pre-plant application of Ridomil Gold at 1-2 pt/A. This would be the same as 1-2 qt of Ultra Flourish or 4-6 qt/A of MetaStar. Apply fungicides in a volume of water or fertilizer that is sufficient for good soil coverage and incorporate into the top 2-4 inches of soil by disking or irrigation.
For light-to-moderate disease pressure, the first application of fungicide can be delayed up to 1 to 2 weeks after transplanting. For extended control of black shank, make a supplemental fungicide application (1 pt of Ridomil, 1 qt of Ultra Flourish, or 2 qt of MetaStar) at layby (around the time the last cultivation is made) OR at first cultivation and again at layby. Sprays made after transplanting should be directed toward the soil and incorporated immediately by cultivation or irrigation (an inch or two of rain will also incorporate these products).