Bougainvillea leaf spot

The disease known as bougainvillea leaf spot is caused by the fungal pathogen Pluripassalora bougainvilleae (formerly Cercospora bougainvilleae). This fungus acts as an obligate or facultative parasite, targeting the foliage of plants within the Bougainvillea genus and causing significant aesthetic and physiological damage.

The primary symptoms manifest as necrotic lesions on the leaves. Initially, small chlorotic spots appear, which gradually expand into larger brown or reddish-brown circular spots, often featuring a distinct halo. In conditions of high ambient humidity, a dusty, grayish layer of fungal spores becomes visible on the underside of the affected leaf tissue.

The development and spread of Pluripassalora bougainvilleae are strongly correlated with prolonged leaf wetness, high humidity levels, and moderate temperatures. The spores are typically dispersed via water splashes during irrigation or rain, as well as by wind currents, which facilitates rapid transmission between plants in close proximity, especially in greenhouse environments.

The impact of this disease on horticultural production is mainly reflected in heavy defoliation, which severely reduces the photosynthetic capacity of the plant. As a result, the vigor of the bougainvillea declines, leading to reduced floral output and an overall stunted appearance, which can be devastating for ornamental trade and display gardens.

Management strategies focus on minimizing leaf wetness and chemical intervention:

• Sanitation by removing and destroying all fallen or infected foliage to reduce the primary inoculum.
• Improving air circulation around plants and ensuring adequate spacing to prevent moisture traps.
• Avoiding overhead irrigation to keep the foliage as dry as possible during the growing season.
• Applying preventive fungicides containing mancozeb, copper, or systemic triazoles when environmental conditions favor disease outbreak.