Brooks County Ag Agent, Garvie Nichols, and I talk about the number of pond questions we receive. The most common pond question I receive pertains to weeds. Generally, pond weeds are treated in the spring and fall. Here is a weed I 
looked at this morning which turned out to be parrotfeather. This plant is also used as an aquarium plant. It is a rooted, submerged perennial plant that usually grows in shallow water. At its base the internodes are longer, and they shorten towards the tip.
It is better to start with a herbicide to manage pond weeds, and sometimes follow up by stocking grass carp. UGA Extension Aquaculture Specialist, Dr. Gary Burtle says that 2,4-D, triclopyr, or imazamox are good chemical for control of parrotfeather.
“Navigate and Weedar 64 is a granular butoxyethyl ester of 2,4-D and has been effective on parrotfeather. 2,4-D compounds are systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.
Reward is a liquid diquat formulation that has been effective on parrotfeather and is very effective if mixed with a copper compound. It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.”
If there are fish in the pond, it is also recommended to treat small portions of the weeds (1/3 at a time) to reduce the risk of oxygen depletion.
Here is a link to the Aquatic Environments section of the UGA Pest Management Handbook which shows weed control options for pond weeds.
Thomas County Ag 