Primary source of inoculum is the spore, which is airborne and can be produced in great numbers from the leaves of infected plants. The spores are very sensitive to light and do not survive long unless protected. They can travel great distances in upper air currents. When they land on a tobacco leaf, they will germinate and penetrate the leaf if a film of water is present. After an incubation period of 5-10 days, symptoms become visible on the leaves.
Sporulation follows soon after.
New spores are produced from the underside of the leaves on a tree-like sporangiophore . The spores are carried by the wind to new plants. Fungicides, systemic or protective. Preventing overwintering of the fungus by removing tobacco plants from greenhouses or other areas where the host might survive the winter. Transplants should be disease-free.