Dave - I think milfoil and coontail are just low on the preference list of plants GC like to eat. The milfoil also seems to start growing well when the water temps are still fairly cold and the milfoil grows faster than the GC can keep up with it early in the spring. I suspect the GC's metablosim is still fairly low when the milfoil is starting to grow strong. It could also be that we simply do not have enough GC stocked in the pond to make a noticable difference in the weeds. We have roughly 6-7 GC per acre in the 2-3 year old range right now, we also have some very old and big GC leftover from when they were stocked in the late 1980's.
There are not very many other paces around here with milfoil in it so it is hard to compare with other ponds. The new NE farm pond book from our G & P does not reccomend GC for controlling milfoil, coontail, duckweed, and FA. They also point out that GC also generate a lot of fetrilizer for new weed growth as a result of their heavy grazing activities.
One of the things that exaserbates the problem in our pond is the water clarity, the clearer the water gets, the deeper the weeds tend to grow up from the bottom. Back in May our sechi disk readings were 108".
I am seriously considering going with a high density stocking of channel catfish in attempt to keep the water clarity down and therefore the weed growth down. I am thinking this might work better than adding more GC.
BTW - I did have a close encounter with one of the GC we origianlly stocked in the late 1980's this last Saturday. This GC was sticking it's tail out of the water while feeding near my boat, the span on just the tail was 13-14" wide.
