Microcoleus

Microcoleus is a genus of filamentous cyanobacteria that, from an agronomic perspective, acts as a soil-surface colonizer. When they multiply rapidly, they form dense biological soil crusts that alter the physical and chemical properties of the substrate, negatively affecting the growing conditions for crops.

The biological activity of these cyanobacteria involves the secretion of extracellular polymeric substances that bind soil particles together. This crust acts as a barrier, sealing the surface of the soil and impeding the vital gaseous exchange between the root system and the atmosphere, which is essential for plant respiration.

Various crops, particularly seedlings of vegetables and small-seeded plants, suffer from the presence of these colonies. The mechanical resistance created by the crust prevents seeds from emerging, while the localized accumulation of cyanobacterial waste products can exert an allelopathic effect, hindering root development.

The primary conditions for the spread of Microcoleus include constant surface moisture combined with high light intensity. These organisms thrive in greenhouse environments using drip irrigation, as well as on agricultural plots where soil surface drying is slow and cultivation practices are infrequent.

• Formation of dark green or brownish leathery crusts on the soil.
• Poor emergence rates and stunted growth in seedlings.
• Increased soil water runoff and reduced infiltration capacity.
• Presence of a slick, gelatinous layer on top of the growing medium.

Management and prevention focus on mechanical disruption of the surface crust through regular hoeing or harrowing to improve soil aeration. Reducing surface moisture, avoiding over-irrigation, and applying organic mulch are effective methods to limit light availability and inhibit the growth of cyanobacterial mats in both field and greenhouse cultivation.