Oval leaf spot

Oval leaf spot is a fungal disease affecting sorghum crops, caused by the pathogen Ramulispora sorghicola (formerly often identified as Cercospora sorghi). This pathogen is widely distributed in sorghum-growing regions globally. It specifically targets the foliage of various sorghum cultivars, leading to significant physiological stress and potential yield degradation in both grain and forage production systems.

The characteristic symptoms include the appearance of oval or elliptical lesions on the leaf blades. These spots initially appear as small discolored areas, eventually developing tan, reddish-brown, or grey centers with distinct darker margins. Under conditions of high humidity, the undersides of these lesions often display small, white, fungal tufts, which represent the conidial sporulation of the pathogen.

The development and spread of Ramulispora sorghicola are favored by prolonged periods of warm and wet weather. The pathogen survives between cropping seasons primarily on infected crop debris left on the soil surface, as well as on contaminated seeds. Spores are easily disseminated to healthy tissues through rain splashes, irrigation water, and wind currents, facilitating rapid spread across the field.

The economic impact of this disease is attributed to the substantial reduction in the effective leaf area available for photosynthesis. This decline in photosynthetic capacity restricts the plant's ability to fill grain and synthesize sugars, ultimately reducing yield quality and quantity. In severe outbreaks, early senescence of the foliage can significantly limit biomass production.

• Practice crop rotation to minimize the build-up of soil-borne inoculum.
• Incorporate crop residue into the soil to promote faster decomposition.
• Select resistant or tolerant sorghum hybrids available in the region.
• Apply certified, fungicide-treated seeds to reduce primary infections.
• Deploy foliar fungicides during the vegetative growth stages if disease symptoms appear early.