There are pond-safe formulations of glyphosate which is the active ingredient in RoundUP, but that kills everything opening you up to erosion. You should try to determine what plants/weeds you want to control so you can choose a herbicide that selectively controls those plants and also is safe near ponds. 2,4-D is a herbicide that kills many herbaceous broad-leaf plants but not many grasses.
FWIW I covered the steep shorelines of our pond with 3 inch rip rap to prevent erosion and then I use AquaNeat (a pond safe glyphosate product) to keep the rip rap area weed free. Our pond is a water table pond so grass for erosion control was not an option for us due to the 3 to 5 foot water level fluctuation.
Bill - that looks awesome - my pond fluctuates too but I have a well that feeds it if I want to maintain the level. Hard to tell in the picture but it appears to be small rock that you are referring to as rip rap?
I guess the Aquaneat product would work on grass and weeds even without the rip rap? Thanks
Yep, the 3 inch rock along the shore and in the waterway are all the same. We can buy rip rap here from 3 to 15 inches. This is an old pic. A bunch of the 3 inch stuff in the waterway washed out this past spring and I replaced it with 12 to 15.
Yes AquaNeat will work without the rip rap. There are several brands of pond safe glyphosate besides Aquaneat such as Rodeo. Just be aware, as RAH said above, once you kill off all the vegetation, you are opening up the possibility of erosion.