Physoderma brown spot

Physoderma brown spot, caused by the fungus Physoderma maydis, is a fungal disease that significantly impacts maize crops globally. The pathogen survives in the soil and on crop debris as dormant sporangia, which are highly resilient structures that can remain viable for several years, waiting for favorable environmental conditions to initiate infection.

This pathogen specifically targets maize plants. Infection typically occurs during the early vegetative stages of growth. The process is triggered when the dormant sporangia are flooded, causing them to release motile zoospores. These zoospores accumulate in the leaf whorl, where they utilize water-filled spaces to infect the developing plant tissues.

The disease is characterized by small, yellow to reddish-brown lesions on the leaves, leaf sheaths, and stalks. As the disease progresses, these lesions turn deep brown or black, representing the maturation of sporangia within the plant tissue. In severe cases, the infected leaf blades may become chlorotic and wither, while stalk infections can compromise structural integrity.

Development and spread of the disease are heavily reliant on moisture and temperature. Warm, wet weather conditions are optimal for the germination of zoospores. Fields with poor drainage or areas where water pools in the leaf whorl for extended periods are at the highest risk for infection. Heavy rainfall and high humidity during the vegetative stages accelerate the disease cycle.

Management of Physoderma brown spot focuses on reducing inoculum levels and minimizing host plant stress. Key practices include:

• Implementing diverse crop rotation to break the disease life cycle.
• Tillage practices that incorporate crop debris deep into the soil to hasten decomposition.
• Improving field drainage to reduce stagnant water.
• Selecting maize hybrids with improved tolerance or resistance to leaf and stalk pathogens.