SQL query using index containing date column uses index in 10g but doesn't in 11g

All;

We are upgrading a system from Oracle 10g to 11g and have notcied some performance degradation in queries that use indexes that contain date columns. We can run teh same query on the 2 databases and see in the plan where it is and is not using the index.
Is there an explanation for the differenence in plans between the 2 databases?
Is there a way across the whole 11g DB that we can encourage the DB to use the date indexes without rewriting the SQL?

See the attachment for query/plan details.

Thanks,

Mark