Panicle blight

The initial signs of panicle blight include discoloration of the florets, which turn brown or greyish. The affected areas lose their firmness and become brittle over time.

A dusty or cottony fungal growth, ranging from white to pinkish or olive, often appears on the surface of the panicles. This indicates active sporulation of the fungus.

Severe infection causes the panicles to deform, curl, or prematurely wither. Consequently, the production of viable seeds ceases entirely, and the inflorescences appear empty or necrotic.

Stems directly below the panicle may show brown streaks or lesions. These lesions may expand as the fungus moves deeper into the vascular tissues of the floral branches.

Microscopic examination of the tissue reveals the presence of hyphae disrupting the cells. Seeds within the panicles remain stunted, shriveled, and fail to mature.

The disease affecting Guinea grass (Panicum maximum) is primarily caused by fungal pathogens, including species of Fusarium and Bipolaris. These fungi target the reproductive structures of the grass.

This is a fungal infection that specifically attacks the inflorescences or panicles of the plant. The mycelium invades the spikelets, disrupting the physiological processes necessary for seed development.

The pathogen survives in crop debris and soil as dormant mycelium or spores. Dissemination occurs primarily through wind currents and rain splashes during periods of high humidity.

Biologically, the fungus colonizes the floral tissues, producing enzymes that degrade the structural integrity of the plant. This leads to the characteristic rotting symptoms in the panicles.

Environmental conditions allow for rapid spore formation, which facilitates the transmission of the disease within the field. The life cycle of the pathogen is closely tied to the reproductive phase of the Guinea grass.

High humidity and prolonged periods of rainfall are the most critical factors for the development of panicle blight. These conditions provide the moisture necessary for fungal spores to germinate.

An optimal temperature range of 20°C to 28°C promotes the rapid growth of the mycelium. In such conditions, the disease can spread across a field in just a few days.

Poor air circulation in dense stands of Guinea grass creates a microclimate with stagnant, moist air. This environment significantly enhances the risk of infection spread.

Nutrient deficiencies, particularly regarding potassium, reduce the plant's overall resistance to fungal invasion. Conversely, excessive nitrogen can create succulent growth that is more susceptible to blight.

Mechanical injuries, whether caused by insects or harsh weather (such as hail), create entry points for the pathogen. Once the surface is breached, colonization proceeds much faster.

The primary impact of panicle blight is the total loss of seed yield. Since Guinea grass is often grown for fodder, the inability to harvest seeds hampers the sustainability of the pasture.

Some fungi associated with this blight can produce mycotoxins. These substances are harmful to livestock if ingested, potentially causing digestive issues or acute toxicity in grazing animals.

The field becomes a reservoir of inoculum, as spores persist in the soil for several years. This limits future crop rotation options and increases the risk for subsequent plantings.

A decline in the overall biological productivity of the field is observed as infected plants weaken. Over time, these patches are often overtaken by invasive weeds.

The economic cost is significant, involving both the loss of forage resources and the expenses associated with fungicide applications and soil remediation efforts.

The first line of defense is the use of high-quality, certified seeds. Treating seeds with a broad-spectrum fungicide before sowing is highly recommended to eliminate early-stage infections.

• Implement a strict crop rotation schedule.
• Mow the grass before the fungus reaches the sporulation stage.
• Practice deep tillage to bury infected plant residues.
• Improve field drainage to prevent excess moisture accumulation.

Systemic fungicides, particularly those containing triazoles or strobilurins, are effective when applied at the booting and early panicle emergence stages to prevent disease establishment.

Providing balanced fertilization with phosphorus and potassium enhances the structural integrity of the plant cell walls, making them harder for the fungus to penetrate.

Regular monitoring of the fields during the reproductive stage allows for early detection. Prompt removal and destruction of infected panicles can significantly reduce the spread of the disease.