Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants Pondweed

esshup is giving accurate info. I would treat asap - the earlier the better. If it were mine I would definitely do as esshup says and importantly knock it out before it has a chance to set seeds by evidence of seed/flower heads at the surface and turtions at leaf axils. CLP is a pest and there are a lot better submerged weeds for a pond than curlyleaf. If you use a brand of Diquat (examples Harvester or Reward) it will knock it out plus other plants quickly before it reaches the surface.
I use Diquat to control my CLP. If you do not aerate the pond with bottom diffuser the Diquat may not be mixed to the bottom zone and will not kill the CLP in the deepest water. Thus regrowth happens again next year. The diquat when applied has to mix into all the CLP stems/leaves especially into the deepest growing plants or diquat does not contact and kill them. Diquat does not last more than a few days unlike Floridone (Sonar) that lasts 40-60 days. If you bottom aerate then what you apply the circulation currents will mix the diquat throughout all the pond depths. According to label 1 gal of Harvester will treat your 1/2 acre with average pond depth 7-8ft.