Sea lettuce

Ulva intestinalis, commonly known as a type of sea lettuce, belongs to the Ulvaceae family. While it is a marine and brackish water algae by nature, it acts as a persistent and invasive weed in agricultural settings, particularly in flooded rice fields where it disrupts cultivation.

This weed is found in various aquatic habitats globally. In agriculture, it thrives in nutrient-rich, stagnant water environments, specifically in irrigation systems and flooded fields where high levels of nitrogen and phosphorus fertilizers provide an ideal substrate for its rapid vegetative growth.

The biology of Ulva intestinalis is characterized by its simple, tube-like thallus and aggressive reproductive strategy. It spreads through spore release and rapid cell division, allowing it to colonize entire irrigation sections within a short period once temperatures and light levels become optimal for photosynthesis.

Its harmfulness is primarily due to shading, which suppresses the germination and early development of rice shoots. Furthermore, the decomposition of accumulated algal biomass creates anoxic conditions in the water column and soil surface, causing root rot and reducing the overall productivity of the crop.

Management strategies focus on both cultural and chemical interventions:

• Water management: Implementing drying periods to disrupt the algae's life cycle.
• Chemical control: Applying selective algaecides approved for rice paddy use.
• Nutrient management: Managing fertilizer runoff to prevent nutrient loading in irrigation water.
• Mechanical clearing: Regular cleaning of water channels to prevent the migration of algal fragments to the main fields.