Blue mold of tobacco was found last week in Caswell County, located in central North Carolina. This is further north than its previous known locations in Florida and Georgia.

The pathogen that causes blue mold is an obligate oomycete, meaning that it requires a living host and it is relatively closely related to Pythium and Phytophthora (the black shank pathogen). A few modern burley varieties have partial resistance to blue mold, but none have what we would consider high resistance; there is no resistance at all in dark tobacco.

Since blue mold is blown in our direction during moist, windy weather, growers are reliant on fungicides for disease management. These options include Quadris, Revus, Forum, Manzate, Orondis Ultra (NOT Gold), Actigard, Aliette, and Presidio. For guidance on choosing a blue mold fungicide, please refer to PPFS-AG-T-08.

Scouting for Blue Mold

Tobacco growers and Extension agents should scout tobacco fields for blue mold in the coming days, particularly since many areas of Kentucky have had rainy weather recently. Focus searches in areas where the pathogen will encounter disease-conducive environments:

• Low spots
• Areas with partial shade
• Lower leaves
• Field locations where water tends to drain slowly

Look for yellow to orange spots on tops of lower leaves (Figure 1), and then turn leaves over to check for blue-gray, somewhat fuzzy sporulation (Figure 2). Sporulation is more abundant under humid conditions, so scouting is most effective when done in early morning or late afternoon. The more recently set plantings will be more susceptible to infection by the blue mold pathogen. However, all tobacco may be considered at-risk, especially crops located east of I-75.

If you suspect tobacco blue mold, please get in touch with your county Extension agent as soon as possible to facilitate rapid identification of this important tobacco disease.

Additional Information

• 2016 Fungicide Guide For Burley And Dark Tobacco (PPFS-AG-T-08)
• Burley and Dark Tobacco Production Guide (ID-190)
• Maintaining The Efficacy of Foliar Fungicides for Tobacco Disease Management (PPFS-AG-T-05)

By Emily Pfeufer, Extension Plant Pathologist