The optimum temperature for incidence of BLB is

The optimum temperature for the incidence of BLB is 22° - 26°C.
Bacterial leaf blight (BLB) develops on the upper leaves of wheat during periods of cool, wet weather, after the plants have reached the boot stage.
Leaf blight disease is caused by the fungus Helminthosporium turcicum Pass. Leaf blight is associated with high relative humidity, wet weather, and cool spring temperatures.