From the label
http://plants.ifas.ufl.edu/guide/sonaras_label.pdfNote: algae (chara, nitella, and filamentous species are
not controlled by Sonar A.S.)
Sonar A.S. herbicide is a selective systemic aquatic herbicide
for management of aquatic vegetation in fresh
water ponds, lakes, reservoirs, drainage canals and irrigation
canals. Sonar A.S. is absorbed from water by
plant shoots and from hydrosoil by the roots of aquatic
vascular plants. It is important to maintain the recommended
concentration of Sonar A.S. in contact with the
target plants for a minimum of 45 days. Rapid water movement
or any condition which results in rapid dilution of
Sonar A.S. in treated water will reduce its effectiveness.
In susceptible plants, Sonar A.S. inhibits the formation
of carotene. In the absence of carotene, chlorophyll is
rapidly degraded by sunlight.