Lesser duckweed

Lesser duckweed (Lemna aequinoctialis) is a small, free-floating aquatic plant belonging to the Araceae family. Recognized as a significant aquatic weed in various agricultural regions, it is known for its ability to multiply rapidly via vegetative budding. This creates thick mats on the water surface, which can completely block light penetration, causing significant ecological and agricultural disruptions.

This species is globally distributed, particularly in tropical and subtropical climates. Its primary agricultural impact is found in rice paddies, where it flourishes in shallow, nutrient-rich, stagnant water. Beyond rice cultivation, it frequently clogs irrigation ditches, drainage canals, and small reservoirs, interfering with water management systems and requiring costly maintenance efforts.

The biology of Lemna aequinoctialis is characterized by an extremely high growth rate. Each individual plant consists of a small frond that produces daughter fronds, leading to exponential population expansion. The weed is highly opportunistic, thriving in conditions with high levels of nitrogen and phosphorus runoff, which are common in intensive agricultural settings.

The economic harm caused by this plant is mainly due to its competitive nature and interference with aquatic life. By forming dense surface covers, it effectively shades out submerged vegetation and lowers the dissolved oxygen concentration in the water column. In rice fields, this shading effect suppresses the growth of young rice seedlings, resulting in reduced vigor and final grain yield loss.

Effective management and control strategies involve a combination of chemical and cultural practices:

• Installing mechanical filters or barriers in irrigation inlets to prevent weed dispersal.
• Implementing integrated nutrient management to reduce phosphorus and nitrogen runoff into water bodies.
• Applying aquatic-labeled herbicides to manage infestations in drainage systems.
• Regular manual or mechanical harvesting to deplete the seed bank and suppress rapid mat expansion.