Zoysia anthracnose

The disease is caused by the pathogenic fungus Colletotrichum zoysiae, which is a member of the Ascomycota division. This pathogen specifically targets turf grasses of the Zoysia genus. It is responsible for causing anthracnose, a destructive disease that can rapidly compromise the health and aesthetic quality of turf surfaces, particularly in high-maintenance lawn environments.

The primary hosts of this fungus are various Zoysia species, such as Zoysia japonica. The fungus infects the foliage and, in severe cases, the crown and root systems of the grass. This parasitic action disrupts the plant's nutrient uptake, leading to visible chlorosis and eventual tissue death. If left unmanaged, it can result in thinning and permanent loss of the turf cover.

Key symptoms include the development of chlorotic spots that eventually turn necrotic or reddish-brown. A diagnostic feature is the presence of acervuli (small black fruiting bodies) on the surface of the blades, which are visible with a hand lens. Affected patches often appear as irregular, blighted areas that may be mistaken for drought stress, but the turf will lack healthy roots and can be pulled up easily.

The development of the fungus is driven by environmental stress and poor management practices. High humidity, warm temperatures, and prolonged moisture on the leaves are critical factors. Overly low mowing heights, soil compaction, and nutrient imbalances—specifically nitrogen excess or potassium deficiency—dramatically increase susceptibility to infection by Colletotrichum zoysiae.

Effective management and prevention strategies include:

• Improving soil drainage to minimize standing water.
• Implementing a regular core aeration schedule to reduce compaction.
• Adjusting mowing height to alleviate stress on the grass.
• Balancing fertility programs with adequate potassium to improve structural resistance.
• Applying preventive or curative fungicides labeled for anthracnose when environmental conditions are conducive to disease.