green head,
We have had tremendous success controlling coontail with Aquathol K and the surfactant, Cide Kick II. We are about to treat a 6 acre pond tomorrow for coontail. The last time we treated this pond for coontail was 5 years ago. The Aquathol K treatment worked well in that instance. Remember that Reward needs a minimum of 48 hours of contact time at the recommended concentration, Aquathol K needs 72 hours, and Sonar needs as much as 90 days. So, depending on your pond, your water exchange may play a large role in deciding what herbicide works best for you.
Another reason I like Aquathol K is it's specific gravity is heavier than water meaning it'll sink through the water column even if you apply it only to the surface. Obviously the more penetration you can get to the deeper water, the better. But at least you have a greater specific gravity helping you out.
Like Greg, we prefer to control creeping water primrose as it's very invasive where we are. Cattail, too, for that matter.
Your pond's characteristics will play an important role in what herbicide you choose.
Good luck!
