Blue-green algae

Blue-green algae (Cyanophyceae), or cyanobacteria, are a group of photosynthetic organisms that can become a significant agricultural concern when they colonize soil surfaces excessively. While they play a role in nitrogen fixation, their mass proliferation creates physical barriers that negatively impact crop establishment and soil structure.

The pathogens involved are various species of cyanobacteria that thrive in wet environments. The primary damage type is physical obstruction; these organisms form dense, mucilaginous mats that interfere with soil aeration and water infiltration, significantly stressing young plants.

Affected crops include various greenhouse vegetables, seedling nurseries, and rice paddies. The symptoms are characterized by a dark green or blue-green, slippery surface film that dries into a hard, cracked crust. This crust prevents delicate seedlings from breaking through the surface and traps moisture, which can encourage damping-off diseases.

Development and spread are triggered by persistent waterlogging, excessive humidity, high levels of phosphorus in the soil, and poor ventilation. In greenhouse environments, the use of stagnant water or high-humidity regimes creates the perfect breeding ground for Cyanophyceae to colonize the topsoil rapidly.

Control measures rely primarily on improving soil management practices. Key strategies include enhancing drainage, reducing excessive irrigation, and implementing regular cultivation or hoeing to break up the surface crust. Using copper-based algaecides or adjusting soil pH through liming can also be effective in reducing the severity of outbreaks.