Collema tenax

Collema tenax is a species of cyanolichen known for forming biological soil crusts. While not a plant pathogen in the traditional sense, its presence in agricultural fields can be problematic as it creates a physical crust that alters the micro-environment of the soil surface, potentially impacting crop establishment and soil moisture dynamics.

The biology of Collema tenax involves a symbiotic relationship between a fungus and Nostoc cyanobacteria. This organism is highly resilient to desiccation, capable of absorbing large amounts of water and swelling rapidly, which leads to the formation of a gelatinous layer that interferes with the germination of small-seeded crops.

Development is most favored on disturbed or uncultivated soils with high mineral content and periodic moisture. In agricultural settings, it is often found in areas with poor crop canopy cover, low soil fertility, or where conservation tillage practices are applied without sufficient attention to surface soil structure maintenance.

Symptoms of infestation include dark, almost black, leathery patches on the soil surface. During dry conditions, these patches become brittle and crusty, whereas under wet conditions, they become soft and slippery. These crusts can restrict water infiltration, causing localized runoff and preventing seeds from emerging through the soil profile.

Management and prevention strategies focus on modifying the soil environment:

• Regular mechanical cultivation to break up the soil surface.
• Enhancing soil fertility to promote faster and denser crop growth.
• Improving soil drainage to prevent prolonged surface wetness.
• Using appropriate crop rotations that provide rapid soil cover to shade out lichen colonies.