Radagast the Brown??

[Inziladun]

Originally Posted by Faramir Jones

We should remember that when Radagast gave Gandalf Saruman's message to go to Isengard, Gandalf suspected absolutely nothing. Saruman, though doing his own thing, was still thought to be an ally. That this was a widely held feeling can be seen at the Council of Elrond, when the truth was told.

Certainly Radagast can't be blamed for trusting Saruman at the time he advised Gandalf to go to Isengard.
But what about after? R. wasn't at the Council of Elrond. The scouts from Rivendell went to Rhosgobel and couldn't find him. It doesn't appear Gandalf ever spoke with him again, at least not until after the War was over. If Radagast never figured out (or, as I think, was never fussed enough about the War against Sauron to really care) that Saruman had turned to evil, there's no reason he wouldn't have kept telling the animals and birds to bring news to Saruman.