Sorghum leaf spot

The pathogen responsible for this disease is the fungus Ascochyta sorghina, classified within the deuteromycetes. The infection primarily targets the aerial parts of the sorghum plant, significantly disrupting photosynthetic processes within the leaves and stems.

This infection affects various sorghum types, including grain sorghum, sweet sorghum, and sudangrass. Crops in regions characterized by moderately humid and warm climates are the most susceptible, especially where intensive crop rotation practices are employed.

Initial symptoms manifest as small, water-soaked spots that gradually expand into oval or elongated lesions. The centers of these spots typically turn grey or straw-colored, surrounded by a distinct dark brown or purple margin. Pycnidia, appearing as tiny black dots, develop within the center of the necrotic lesions.

The development of Ascochyta sorghina is facilitated by high humidity, frequent rainfall, and moderate temperatures ranging from 20 to 25°C. The fungus persists on crop debris in the soil and on infected seeds, which serve as primary inoculum sources at the start of the growing season.

The economic damage caused by this leaf spot involves premature leaf senescence, leading to a reduction in the plant's photosynthetic surface area. Consequently, this leads to decreased grain mass, lower grain quality, and reduced yields of total green biomass in forage sorghum varieties.

• Implementing a crop rotation cycle that excludes sorghum for at least three years.
• Thorough plowing under and destruction of infected crop residues.
• Utilization of high-quality, treated seed materials.
• Selection and cultivation of resistant sorghum hybrids adapted to local conditions.
• Application of appropriate fungicides upon the detection of early disease symptoms.