Familiar diseases, such as black spot, fireblight and apple scab require moisture to spread to and infect new host plants. Constantly wet foliage from overhead watering is a condition that promotes disease development. Seedlings grown indoors in soggy, unsterilized potting medium and pots are more prone to damping-off, a fungal disease. Each disease pathogen has a specific temperature range for growth and activity. Many powdery mildew diseases are late summer, warmer temperature diseases.
Temperature affects how rapidly pathogens multiply.
Soil temperature can also be critical for disease infection. Cool, wet soils promote fungal root diseases. Temperature extremes can cause stress in host plants, increasing susceptibility. The combination of wind and sun affects how quickly plant surfaces dry. Faster drying generally reduces the opportunity for infection.