We looked at a pond yesterday which was about 1.5 acres, spring fed and covered in some weeds. Weeds in ponds are placed in one of three categories: submersed, emersed, or floating. These weeds were coming from the bottom of the pond and sticking out, which are emersed. UGA Extension Aquaculture Specialist, Dr. Gary Burtle, helped us ID the weeds. The short weed is southern water grass which has some emergent parts and some submerged parts. The other plant is torpedograss. It is the tall grass with the panic-grass seed head.
Both weeds respond to glyphosate if enough of it is emergent in order to obtain a good treatment. Dr. Burtle says one problem is that glyphosate does not seem to translocate into the underwater portion of plants as well. If the weed is submerged more than 25%, the herbicides have less effect. For this reason, tt is recommended to use a sticker/spreader adjuvant, like a crop oil. Also, stocking 10 grass carp triploids per acre after the weeds have decomposed would help.
This pond does have bass which is very risky to treat during hot time of the year. As the plants decay, fish can die from result of oxygen depletion. Instead of treating the entire pond at one time, it is best to treat 1/3 or 1/4 sections at a time.