Crazy top of maize

The causal agent of this disease is the oomycete Peronosclerospora spontanea, a pathogen known for causing systemic downy mildew in several grass species. As an obligate parasite, it disrupts the hormonal balance of the host plant, leading to profound developmental abnormalities and significant reduction in photosynthetic efficiency.

Maize is the primary economic host for this pathogen. The infection cycle usually begins when spores germinate in the soil or on seeds, penetrating the developing seedlings. Once inside, the mycelium spreads systematically throughout the plant, meaning every part of the mature maize plant can become infected and serve as a secondary inoculum source.

Symptoms are often dramatic, leading to the common name "crazy top." Infected plants exhibit chlorotic streaks, stunted growth, shortened internodes, and often show excessive proliferation of axillary buds. In severe cases, the reproductive organs, such as tassels and ears, are malformed or replaced by leafy, sterile structures, rendering the plant completely unproductive.

The spread and development of Peronosclerospora spontanea are highly dependent on environmental factors. High humidity and temperatures ranging from 20 to 25 degrees Celsius create the perfect conditions for conidial production and dissemination. Wind currents facilitate the rapid movement of spores across fields, allowing the disease to progress quickly during wet seasons.

Management of this disease requires a multifaceted approach to break the infection cycle:

• Deploying resistant maize hybrids that show lower susceptibility to systemic infection.
• Applying systemic fungicides as seed treatments to protect young seedlings.
• Implementing strict crop rotation to reduce inoculum pressure in the soil.
• Maintaining field hygiene by removing crop debris and volunteer maize plants that harbor the pathogen.