I've been watching this thread with interest. One thing I can definitely agree with, Watermeal is one tough hombre. I really hope the money you spent on Diquat was not wasted. If your spray treatments have indeed reduced the Watermeal, that is good news. Nothing has ever worked on Watermeal for me except Fluridone. Yes, it is expensive but it does work.
I have a 3/4 acre pond that was completely covered with Watermeal. One quart of Whitecap applied in early May last year killed all the Watermeal and most of the other vegetation. It is over one year later and no signs of Watermeal but the submerged and emergent plants have come back. I'm expecting the Watermeal to return but I have another quart of Whitecap on hand to stop it in its tracks! If your pond is smaller than 1/2 acre and the infestion is not severe, I suspect that 1 quart of Whitecap may be enough for 2 treatments but I will defer to Greg and the other experts on that.
