Etiology:

• Facultative saprophyte
• Conidiophores: 2-6 in number, emerge from stomata, brown in color, 2-4 septa
• Conidia: 3-8 septa (may be true or pseudo),Straight or slightly curved, widest at the center, presence of hilum

Fig: Conidia

Favorable condition:

• Relatively cool, wet seasons, 6 hours of leaf wetness, temperature 18 and 27 °C
• Sporulation requires a 14-hour dew period between 20 and 25 °C.
• Sporulation often occurs during nighttime and is halted when humidity falls during the day.

Infection is inhibited by high light intensity and warm temperatures.