Passalora sheath spot of sugarcane

The causative agent of this disease is the ascomycete fungus Passalora vaginae, previously classified as Cercospora vaginae. This phytopathogen specializes in infecting the vegetative organs of sugarcane, inducing specific necrotic lesions on the leaf sheaths that significantly impact the physiological health of the plant.

The primary host for this fungus is sugarcane (Saccharum officinarum). The pathogen resides mainly on the leaf sheaths, which tightly envelope the stem, creating a microenvironment highly conducive to mycelial growth under conditions of high humidity and moderate ambient temperatures.

The symptoms of the disease appear as elongated spots ranging in color from dark red to purple or brown on the surface of the leaf sheaths. As the infection progresses, these lesions can merge, affecting large areas of the tissue. In the centers of the infected areas, the fungus often produces conidia, appearing as a dark, dusty growth.

The development of Passalora vaginae is favored by conditions of high humidity and temperatures between 20°C and 28°C. The infection spreads via conidia dispersed by wind, rain splashes, or during field operations. Dense canopy growth and poor air circulation significantly exacerbate the risk of widespread infection within sugarcane plantations.

The economic impact of the disease lies in the impairment of metabolic processes within the sugarcane stalks. While sheath infection rarely results in total plant mortality, it decreases photosynthetic efficiency and overall raw material quality. In severe cases, the fungus may facilitate secondary rot, leading to lower sugar extraction rates during processing.

Control measures rely primarily on the use of disease-resistant varieties and healthy planting stock. Essential agricultural practices include maintaining optimal plant spacing to promote air circulation, prompt removal and destruction of crop residues post-harvest, and implementing crop rotation schemes to break the survival cycle of the fungus in the field.