Producers should begin scouting for blue mold

By Katie Pratt

(June, 2008) –With reports of blue mold as far north as southern Virginia, Kentucky tobacco producers should begin scouting their fields and thinking about taking measures to prevent the disease, said Kenny Seebold, University of Kentucky College of Agriculture extension plant pathologist.

“It’s important for producers to keep an eye on where it is and if the weather favors diseases,” he said.

Blue mold is caused by Peronospora tabacina, an airborne pathogen. The pathogen overwinters in warmer climates and is transported north by weather systems that move in from the South. Infected plants will have a blue-gray mold on the back of their leaves.

Blue mold annually shows up in the state, but the time it appears depends on the weather. Seebold said, on average, blue mold begins appearing in the state as early as the third week of June and as late as the second week of July. It usually first appears in low and shaded areas.

Dry, hot weather, like the state recently experienced, does not promote the spread of blue mold. However, producers should watch the weather for systems and tropical storms that could carry the pathogen northward. Consecutive days of rain could also increase the risk of blue mold because it thrives in cool, damp conditions much like the state had this spring. 

“We feel like we dodged a bullet this spring,” Seebold said. “We had the perfect conditions for blue mold. We would have been in serious danger if we had gotten spores during the transplant production cycle.”

The last major outbreak of blue mold in the state was in 2006. Outbreaks also occurred in 2003, 2004 and 2005. Blue mold appeared in the state last year, but the hot, dry temperatures kept the disease at bay.

Producers can use several chemicals as preventative measures including Quadris, an Acrobat or Forum tank mixed with mancozeb, which is found in either Dithane DF or Manzate Prostick, or Actigard. Actigard is effective against blue mold, but should not be applied to burley tobacco until the plants are at least 18 inches tall or 12 inches tall for dark tobacco. Actigard needs to be applied before an infection to function at its best. Two or three applications of Actigard about 10 days apart during the growing season should protect the plants through topping, which is when the risk for blue mold significantly decreases. The other chemical options work best when applied before the disease becomes established, or when symptoms are first noticed at the very latest.

If blue mold appears in a field, it is important for a producer to access the extent of the damage and determine which type of fungicide treatment to use. Any blue mold occurrences should be reported to the local Cooperative Extension Service’s  agriculture and natural resources agent so they can inform others in the community and help state specialists monitor the spread of the disease.