These are just 2 of the herbicides that are effective on controlling Aquatic Weeds.
Metsulfuron
A selective herbicide widely used for controlling Alligator Weed (noxious). Although it is somewhat effective against the Alligator Weed, the herbicide is like other chemicals controlling this weed, slow to reach the underwater root system and the weed re-grows. The recommended treatment for this weed is continuing spray treatments 3 times a year for several years until eradications becomes evident.
Bi-Active Roundup (Glyphosate)
Fully registered for over 100 weeds and trees and is also somewhat effective controlling Alligator Weed but Metsufuron is the preferred option. The Bi-Active Roundup is a new formulation for improved weed control in aquatic & sensitive public areas. This herbicide is much more friendly to use in aquatic applications and extremely effective on several species of Aquatic Weed.
Application Issues
Some Alligator Weed herbicide applications are sprayed and left to sink to the bottom of the waterway and rot instead of removing the dead weed from the water. Even allowing the sprayed material to rot in the water can cause dissolved oxygen depletion which can kill aquatic life. Spray drift is another critical issue and must be well controlled so as to not impact on untargeted flora and fauna. When spraying in waterways that are used for irrigation and potable use, most labels will restrict spraying within .5 klm from any water withdrawal point. Alligator Weed also grows well on land particularly in riparian areas and herbicide mix rates need to be strictly adhered to when treating these areas in case a rise in water level covers the sprayed area and contaminates the waterway.