Rootless duckweed

Rootless duckweed, scientifically known as Wolffia arrhiza, belongs to the Araceae family and is classified as a free-floating aquatic macrophyte. It is recognized as the smallest flowering plant on Earth, appearing as tiny green granular thalli floating on the water surface. Due to its extreme reproductive capacity, it can transform a clear pond into a dense green carpet within a matter of days during the warm growing season.

This weed is primarily found in stagnant or slow-moving waters, including ponds, lakes, and marshes. Its impact on agriculture is particularly severe in irrigated fields and rice paddies. Wolffia clogs irrigation canals, interferes with water transport, and impairs the functionality of hydraulic infrastructure. In rice production, it can suppress the growth of young seedlings by blocking light and competing for nutrients.

The biology of Wolffia is characterized by a complete absence of roots and a highly efficient mode of asexual reproduction. It thrives in nutrient-rich (eutrophic) water, especially where nitrogen and phosphorus levels are high. The plant is temperature-dependent, showing rapid population explosions when conditions are optimal, while moving to the bottom of the water column to overwinter during colder periods.

The damage caused by Wolffia extends beyond physical obstruction. By covering the entire surface of a water body, it prevents atmospheric oxygen from dissolving into the water, leading to hypoxic conditions that harm beneficial aquatic life. Furthermore, when large populations die off, the decomposition process can drastically reduce water quality, causing odor issues and promoting the growth of opportunistic bacterial pathogens.

Effective control measures require an integrated approach:

• Mechanical removal using surface skimmers or specialized nets to clear canals.
• Improving water flow rates in irrigation channels, as Wolffia struggles to propagate in fast-moving water.
• Nutrient management in surrounding fields to reduce runoff of fertilizers into water systems.
• Application of approved aquatic herbicides when manual control is insufficient.
• Biological control through the introduction of herbivorous fish species that consume floating vegetation.