Shields are absolutely necessary for any radios hung on the same mast. Homemade shields described below will work, but you might as well just buy the $28 prefab RF Armor shields for Nanostation here and Nanostation Loco here.
Despite better judgment, I have been rolling out some nifty homebrew "RF Armor" style shields on Nanostations and Nanostation Locos. They yield particular benefit for any radios mounted on the same mast. Indeed, I'd say such shields are required for co-located radios, even with 2.4GHz and 5.8GHz units.