Is there anything that you can spray on duckweed that only kills duckweed? Thanks

Our engineers tell us that goldfish will control duckweed. They are occasionally stocked in our wastewater lagoons for this specific purpose. I have put duckweed in my wine barrel pond with goldfish and it doesn't last more than a week. Then again, i never feed them so their probably awefully hungry. Good luck.

Almost a trick question. First, the most effective treatment for duckweed with a herbicide is not sprayed on at all. You would either use granular or liqoud, mixed in the pond slow release Fluridone is best. And no, there is no herbicide that I know of that is duckweed selective. In fact, I have seen many used improperly, killing everything but the duckweed.

I agree with PF. DW is the most difficult weed I have dealt with.