How does rose black spot spread in the environment?

Sourav PanNovember 14, 2024

Answered

Rose black spot, caused by the fungus Diplocarpon rosae, spreads primarily through environmental factors that facilitate the movement of its spores. Here’s how the disease propagates in the environment:

Mechanisms of Spread

1. Water Splash: The spores, known as conidia, are dispersed from infected leaves or canes by splashing water, which can occur during rain or overhead irrigation. This is a crucial method of transmission, as it allows spores to reach newly emerging leaves on the same or nearby plants.
2. Humidity and Wet Conditions: For infection to occur, leaf surfaces must remain wet for a minimum of seven hours. High humidity (above 90%) and moisture are essential for spore germination and subsequent infection. The ideal temperature range for disease development is between 65°F to 75°F (approximately 18°C to 24°C).
3. Overwintering: The fungus survives the winter in fallen leaves and infected canes, where it forms fruiting structures called acervuli. These structures produce new spores in the spring, which are then released into the environment during wet conditions.
4. Secondary Infections: Once the initial infection occurs, new acervuli develop within two weeks on infected tissues, releasing additional spores that can cause further infections throughout the growing season. This cycle can repeat multiple times if conditions remain favorable.

Environmental Conditions Favoring Spread

• Cool and Wet Weather: The disease is most active during cool, moist spring days and humid nights, which provide ideal conditions for spore germination and infection.
• Temperature Sensitivity: While warm temperatures promote fungal growth, temperatures above 85°F (29°C) can inhibit the spread of the disease, making hot and dry conditions less conducive for infection