Leaf spot diseases are usually worse in which conditions?

• A. Dry weather
• B. Cool nights
• C. Wet or humid weather
• D. Windy conditions

Answer: (C)

Leaf spot diseases rely on moisture on the leaf surface to infect and multiply. Wet or humid weather creates and maintains leaf wetness from rain, dew, or overhead irrigation, giving fungal or bacterial spores the opportunity to germinate, penetrate leaf tissue, and establish new infections. High humidity also supports the pathogen’s life cycle and spread, so symptoms become more widespread and severe. Dry weather dries the leaves, limiting infection, while wind may help spread spores but can’t drive disease without leaf moisture first. Cool nights can reduce evaporation a bit, but the decisive factor is sustained leaf wetness from wet or humid conditions.