Aerial dispersal and drying of Peronospora tabacina conidia in tobacco shade tents.

Blue mold of tobacco is caused by the fungus Peronospora tabacina. Its spores are released in the morning when the relative humidity falls, but they require free water for germination. Traditionally, the walls of the shade tents are raised to control the pathogen by drying leaves. We show that raising the walls does not materially speed drying. It does, however, increase the wind speed at least 20 m inside the tent and spread spores farther. Because germination is not reduced, raising the walls may actually spread blue mold.