sql query taking long time

We are using database version 11.2.0.2

We have the following query that is taking a long time. We do have a primary key index on productdata table on column prd_info_id and a composite index with prd_info_id column included on testdata table. The only thing is we don't have an index on upd_date column on testdata table. I am going to try to create an index on the upd_date column and see if the query will speed up. Gurus, any suggestion here? Please advise. Thank you.

 

select productdata.serial_no, testdata.tst_ivalue,

 

testdata.tst_judge, testdata.tst_rvalue,