Reward will only burn the plant and not kill the root which means you will be retreating. The 2,4-D product that was posted is not for use in aquatic environments and I am 99% positive that Willows are dicots(Broadleafs) which means it should work but look at DMA-4 which is approved for your pond. I prefer Habitat or would even spend my money on an aquatic roundup like Rodeo or ShoreKleer. Add a surfactant and you are in business. Just remember by killing the willows you will still have dead biomass to remove.
