I've been having a major battle with watermeal this summer.
In early July, it had covered practically the entire pond. My pond is about 0.2 acres.
I bought Flumioxazin and applied it on the pond surface at the recommended rate of 5 ounces. It appeared to have an excellent effect, and the watermeal mostly disappeared for a week or so. I knew it would likely return, so I was ready for it, and sure enough, it did begin to spread again.
I surface sprayed it again. This time, the watermeal turned brown, but did not disappear, and within a few days, it turned green again and began to spread. I have treated it several more times, roughly weekly, by surface spraying and each time it did the same thing - turned brown for a couple of days, then became green again and began spreading. Then I tried a subsurface application, using about 12 ounces of Flumioxazin, the recommended amount for my pond size. The effect was the same, brown briefly, then green again. At this point, I am out of guesses. Everything I've read says Flumioxazin is the best herbicide to use on watermeal, but it just isn't getting the job done. Any suggestions? My pond is 0.2 acres, with an average depth of 4 feet.
BTW, at the same time that I began to battle the watermeal, I added an aeration disk to the pond, to prevent fish kill while battling the watermeal. I do turn off the aeration for a day after applying Flumioxazin to make sure it stays on the surface and doesn't mix into the whole pond depth.
