The Black Spot fungus is usually present on which part of the leaf?

The Black Spot fungus, which is responsible for a common plant disease in roses and other plants, primarily manifests on the upper surface of leaves. This is crucial because the upper leaf surface is where the majority of sunlight exposure occurs, making it an ideal environment for the spores of the fungus to germinate and thrive. The presence of moisture, combined with specific temperatures, further promotes the growth of this fungus on the upper leaf area, leading to the characteristic black spots that can severely damage the plant's photosynthetic ability.

In contrast, the lower surface of the leaf is often more shaded and may not provide the same conducive environment for the fungus. While the middle and edges of the leaf can experience fungal infections, the upper surface is where the initial infection is most likely to occur and where it is most notably visible. This differentiation is important for effective disease management in horticulture.