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.
Know the label; know the law
Avoid “over-the-top” applications of fungicide after the last cultivation because of the difficulties in getting chemical down to the soil surface as plants begin to spread out. Any chemical that contacts tobacco leaves will not be taken up by the roots, and will not be available to protect against black shank. Do not make supplemental applications if more than 1 pt of Ridomil Gold, 1 qt of UltraFlourish, or 2 qt of MetaStar was used at planting. Do not exceed the equivalent of 1.5 lb a.i./A of mefenoxam per season (3 pt of Ridomil Gold or, 3 qt of Ultra Flourish, or 6 qt of MetaStar).
Over the years, growers have wondered if it would be possible to add Ridomil Gold to the setter barrel and apply the fungicide in transplant water. Until recently, adding Ridomil tobacco setter water was not supported by the product label, although many probably ‘experimented’ with this off-label method.
There are some obvious advantages to using Ridomil in the setter barrel – fungicide is placed directly into the root zone of newly-set plants, where it can be taken up quickly. Also, the cost of application can be reduced because less chemical is used compared to broadcast treatments and treatments can be applied during setting. This saves trips across the field to apply and incorporate Ridomil before transplanting.
As mentioned earlier, this type of application was not legal; however, in March of 2011, several states (Georgia, Kentucky, Indiana, Ohio, North Carolina, Tennessee, and Virginia) approved the use of Ridomil Gold SL as a setter-water treatment for the control of black shank on burley, dark and flue-cured tobacco. The special local-need label, or 24(c), was granted after several years of testing in these states.
Setter-water treatments with Ridomil will work best for growers using sound management practices (sanitation and crop rotation) along with one of the newer resistant varieties, and who are looking for additional protection from black shank. In these cases, it will be possible to get adequate control of disease and also reduce fungicide costs by approximately $70 per acre.
Where disease pressure is high, particularly if limited crop rotation is being practiced, or where varieties with little or no resistance are being planted in fields at risk to black shank, broadcast-applied Ridomil at 1-2 pt/A would be a more effective treatment, based on our research.
To get the best results from Ridomil Gold SL when applying in transplant water:
- Use good management practices and plant a variety with moderate to high resistance to race 0 and race 1 black shank.
- Use only Ridomil Gold SL in setter water. Ridomil Gold EC and Ridomil 2EC contain high levels of solvents and can injure or kill tobacco seedlings. Likewise, avoid generic versions of mefenoxam or metalaxyl. Only Ridomil Gold SL is covered by the Special Local Need Label.
- Add 4 to 8 fl oz/A of Ridomil Gold SL to no less than 200 gal/A of transplant water to avoid injury to tobacco. Use the high rate in areas with a greater risk of black shank.
- Make 1-2 supplemental, soil-directed applications at 1 pt/A if needed to provide control of disease.
- Do not apply Ridomil Gold SL to stressed or weak seedlings, or during hot, dry conditions to avoid serious plant injury.
- Mix thoroughly before transplanting. Using a separate tank to pre-mix Ridomil Gold SL will help ensure thorough mixing and a consistent concentration of fungicide during transplanting, resulting in less injury potential and better control of disease.
- The user must have a copy of the Special Local Need label in their possession at the time of application.