Anacystis dimidiata

Anacystis dimidiata is a microscopic cyanobacterium commonly found in wet soils and flooded agricultural environments. In agronomy, it is recognized for its ability to form dense algal mats that interfere with the normal development of crops, particularly in paddy fields. Although it functions as an aquatic weed, its rapid biomass production can significantly impact crop yields.

The primary crop affected by this organism is rice (Oryza sativa). The presence of these algae creates an environment unsuitable for seedling establishment, as the algal mass physically covers the soil surface. This coverage reduces the amount of light reaching the submerged seeds and prevents oxygen exchange, leading to stunted growth or total seedling loss.

The symptoms are characterized by the appearance of bright blue-green or dark slimy mats on the surface of the water or wet substrate. As these mats age and dry, they form a persistent crust that acts as a mechanical obstacle. Plants often exhibit chlorosis or delayed development due to the competitive depletion of soil nutrients by the algal colony.

Development and spread are primarily driven by stagnant water, high ambient temperatures, and an abundance of nitrogen and phosphorus in the soil-water interface. These nutrient-rich conditions promote rapid cellular division, allowing the organism to cover large areas within a few days, particularly during the early vegetative stages of the crop.

Effective protection measures involve both biological and chemical strategies. Managing water levels through proper drainage and re-flooding cycles can disrupt the life cycle of the algae. Additionally, the application of copper-based algaecides or specific herbicides remains a standard practice to suppress the growth of Anacystis dimidiata and ensure healthy crop progression without harmful competition.