Does any know a way to controll excess grass in an earth pond. Pond is almost 1/2 arce, 13-14 ft deep at the north end, 3-12 inch at the south end. We are planning to plant several weeping willows to decrease the sunlight on that end & hopefully help control the grass somewhat.* Will this help? Does anyone have any other ideas. We have tried comercial chemicals without any effects. Sorry can not seem to get the pic the correct size to download.