It is very prevalent in humid farming zones, like the southeastern and Eastern U.S., Canada, and countries bordering the Caribbean.

There was approximately twenty five million dollars in losses which is nearly thirty percent of tobacco plants at the time.

[1] Each year, Peronospora hyoscyami is introduced as blue mold as windblown spores from outside the region by infected transplants.

Tobacco plants with an upright position of small patches of the seed bed are typically early signs of blue mold.

These leaves are usually 2–4 centimetres (0.79–1.57 in) in diameter, and normally spotted with yellow, gray, or a bluish mold in the lower surface.

The oomycete frequently takes place when the vein of the leaves reaches vascular tissue of the stem, causing weakness and lodging.

The rate of continental spread is based on the potential for high levels of inoculum and effective wind spores.

[3] After the germination of conidia, the initial penetration of the host depends on the formation of appressoria near the stomata.

[4] Upon entry of an infection peg through a stomatal opening, hyphae grow and develop between plant cells.

[5] The activation of systemic acquired resistance (SAR) has shown to be an effective management strategy for P. hyoscyami f.sp.

[6] In addition, PR proteins have been shown to have antifungal activities in vitro and thus are thought to be a key component in the resistance of tobacco to blue mold.

In addition to SAR, tobacco plants have been found to secrete β–ionone and T-phylloplanin which both inhibit the sporulation and growth of P. hyoscyami f.sp.