Hairless perennial, roots in <2m water, forms floating mats extending out from banks covering surface of deeper water; also grows on land. White clover-like flowers (summer). Waxy green leaves in opposite pairs with midrib. Green-brown stems often red tinged; root at nodes.
Waterways from 0–30% salinity (eg estuaries, dune lakes, wetlands), pastures & urban areas. Grows best in fertile conditions with warm growing season. Cold winters tolerated but is frost tender.
Stem fragments lodge in stream banks, and establish new colonies. Easily spread by cultivation, boats and nets.
Restricts water flow, increases sedimentation, causes flooding. Impedes access to water. Invades pasture and cultivated land. Can cause photosensitivity in stock that eat it.
Spraying over water may require resource consent. Requires frequent follow up. Exclude livestock, maintain riparian plantings to lower nutrient runoff and lower light level. Lower water level wherever possible to use terrestrial spray methods.
1. Ensure presence of Agasicles hygrophila & Arcola malloi biocontrol agents; very slow acting, only effective late in season, where plants grow over water.
2. Dig out small patches removing all stem fragments; check for regrowth.
3. Cover with weedmat for 6-12 months; check edges for creeping stems.
4. Weed wipe (land) (5g metsulfuron + 1ml penetrant/1L).
5. Spray terrestrial sites spring -autumn (5g metsulfuron + 10ml penetrant/10L). Take extreme care around waterways.
Caution: when using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.