State tax filing

This is why I ask this question, here, on turbotax. TT is my "tax advisor"

 

On my own, I have found out that if a fund holds 100% US government securities, than interest from that fund is free from state tax.  What I need to know is the minimum percentage of government securities a fund most hold, it may be 50% for example, to be exempt from state tax.

 

Anyone know this for Oregon?