Effect of Dew Period on Leaf Surface on the Leaf Spot Disease of Flue-cured Tobacco Caused by Corynespora Cassiicola

When inoculated plants were placed in a moist chamber for 12 hours only or 12 hours every night, the disease occurred slightly. When inoculated plants were placed in a moist chamber for 24~36 hours, the disease occurred obviously, and for 48~72 hours occur severely. We proposed that the continuous raining and > 24 hours dew period on surface were two prerequisites for the disease obvious or servere occurance.