Iliau

The earliest symptoms of Iliau include the appearance of small, reddish-brown spots on the leaf sheaths of young shoots. These spots eventually enlarge, coalescing into larger necrotic lesions that can girdle the entire stalk.

A distinctive feature of the infection is the development of a white or grayish mold on the surface of the stalks. This white coating is composed of the fruiting bodies and spores of the fungus, giving the stalks a dusty appearance.

Affected plants exhibit severely stunted growth, with shortened internodes. The leaves often curl, turn yellow, and eventually become necrotic, leading to the overall collapse of the shoot.

The buds on the infected stalks are frequently killed before they can germinate, resulting in gaps in the sugarcane stands. If a stalk is cut open, the internal tissue may show dark, decaying areas accompanied by a musty odor.

• Reddish lesions on leaf sheaths.
• Grayish fungal growth on stalks.
• Severe stunting of young plants.
• Curling and wilting of apical leaves.
• Death of lateral buds.

The causative agent of the disease is the fungus Gnomonia iliau. This pathogen specifically targets the young, actively growing tissues of sugarcane, leading to systemic damage during the early developmental stages of the crop.

The fungus survives primarily in crop debris and infected stalk tissues. Under favorable conditions, it produces spores that are easily disseminated by wind and rain splashes, allowing the disease to spread rapidly throughout a field.

Infection begins when spores land on young leaf sheaths or near the buds of the stalks. The fungus secretes enzymatic complexes that break down plant cell walls, allowing the mycelium to penetrate and colonize the internal tissues.

Once inside, the pathogen restricts the transport of water and nutrients, which inhibits the metabolic activity of the sugarcane plant. This interference often results in stunted growth and the death of young shoots.

Scientific research indicates that Gnomonia iliau is highly persistent, capable of remaining latent within dormant buds until environmental conditions trigger its vegetative growth.

Iliau is most prevalent in cool and humid environments. Periods of prolonged rainfall combined with moderate temperatures (around 15°C to 22°C) provide the ideal conditions for the rapid germination of spores and infection.

High-density planting creates a stagnant microclimate within the sugarcane field. Increased humidity around the base of the stalks prevents moisture from evaporating, which significantly promotes fungal development.

The use of infected setts (seed cane) is the most common method of introducing the pathogen into a new area. Since the fungus can reside inside the cuttings, it spreads silently from one region to another.

Poor soil drainage and waterlogging weaken the plant's natural defenses, making the sugarcane more susceptible to infection. Optimal soil management is crucial to maintain plant vigor against potential pathogens.

Field conditions characterized by an accumulation of crop debris from previous harvests provide a continuous supply of inoculum, maintaining the disease cycle year after year.

The primary economic harm caused by Iliau is the reduction in stand density due to the failure of young shoots to develop properly. This requires significant replanting, increasing operational costs.

The disease reduces the quality of the harvest. By damaging the vascular system, the fungus lowers the sugar concentration in the juice, which negatively affects the overall industrial yield.

Infected stalks are often fragile and prone to breakage. This vulnerability makes mechanical harvesting difficult and leads to considerable crop losses before the sugarcane reaches the factory.

Secondary infections often take hold in the damaged tissues, accelerating the decomposition of the stalk. This rotting process can render large portions of the crop unsuitable for processing.

Furthermore, the disease reduces the longevity of the sugarcane crop, preventing the field from being harvested as a ratoon crop in subsequent years, thus shortening the production cycle.

The most effective strategy is the use of disease-free planting material. Growers should only obtain seed cane from certified nurseries that practice rigorous phytosanitary monitoring.

Hot water treatment of setts, typically at 50-52°C for approximately 30 minutes, is a proven method for eradicating Gnomonia iliau from the planting material before it enters the soil.

Crop rotation with non-host species is essential for breaking the disease cycle. Implementing a fallow period or rotating with legumes for 2-3 years helps to deplete the population of fungal spores in the soil.

Sanitation practices are mandatory. After harvest, all crop residues should be removed and destroyed, either by deep plowing or burning, to eliminate the pathogen's reservoir.

While fungicidal sprays can be applied in high-risk areas to protect developing shoots, they should be used as a secondary measure in conjunction with strict cultural practices and resistant cultivar selection.