Plectonema

Plectonema is a genus of filamentous cyanobacteria (blue-green algae) often encountered in agricultural environments, particularly in greenhouses, hydroponic systems, and irrigation networks. While not a direct plant pathogen like fungi, it is considered a pest due to its aggressive colonization of infrastructure and growing media.

The primary impact of Plectonema is categorized as biofouling. It forms dense, slippery mats on surfaces that interfere with equipment performance. In hydroponic setups, it competes for space and nutrients, potentially causing localized hypoxia in the rhizosphere by covering roots and substrate surfaces, which hinders plant growth.

Symptoms of infestation include the appearance of dark green, blackish, or blue-green slimy layers on damp surfaces. In irrigation systems, the presence of these algae is identified by clogs in emitters, drippers, and filtration screens. The reduction in water flow is the most common diagnostic sign that a biofouling problem is present.

The proliferation of Plectonema is driven by optimal conditions: high light intensity, warm temperatures, and high nutrient levels (nitrogen and phosphorus). These cyanobacteria thrive in stagnant water and damp substrates, quickly multiplying when irrigation lines are not properly maintained or shielded from light.

Protection and preventive measures focus on physical and chemical sanitation:

• Shading irrigation tanks and reservoirs to prevent photosynthesis.
• Applying specific algicides or hydrogen peroxide to disinfect lines between crops.
• Installing UV sterilization units to treat nutrient solutions and water supplies.
• Regular manual cleaning of filters and emitters to prevent blockage.