Newtx,

Don't use Roundup, even small amounts can be harmful to the fish...see this article

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=14;t=000136

I've had outstanding success with Reward on small willows...it really burns them and they don't seem to come back, even though it isn't a systemic killer as I understand. Kelly will correct me if I'm wrong, which I probably am....