Sorghum downy mildew

Pathogen and disease type. The disease is caused by the oomycete Peronosclerospora sorghi, which leads to a systemic condition known as sorghum downy mildew. As an obligate parasite, it colonizes the host plant internally, systemically invading the vascular tissues and significantly affecting plant physiological processes.

Affected crops and damage. The primary host is sorghum, though the pathogen can also infect maize. The economic impact is severe, as infected plants often exhibit stunted growth, chlorosis, and reduced grain production. In extreme cases, the disease leads to total crop failure and significant reductions in stand density due to plant mortality.

Symptoms and signs. Early symptoms appear as chlorotic stripes on young leaves. During periods of high humidity, a characteristic white to grey downy fungal growth appears on the undersides of the leaves, representing the sporulation of the pathogen. Systemically infected plants often show a bushy appearance and may fail to produce grain-bearing panicles.

Conditions for development. The development of Peronosclerospora sorghi is favored by high soil moisture and moderate temperatures, typically between 15 and 25 degrees Celsius. The pathogen survives in the soil as thick-walled oospores, which can remain dormant for several years, while air-borne conidia facilitate rapid spread during the growing season.

Protection and control. Integrated management is essential for controlling this disease. Key strategies include the deployment of genetically resistant sorghum hybrids and strict crop rotation to reduce inoculum levels in the soil.

• Seed treatment with systemic fungicides.
• Removal and destruction of infected plant debris.
• Use of disease-free certified seeds.
• Monitoring fields for early detection and localized treatment.