how to split, remove part of data in column with spreadsheet gem

Using spreadsheet gem and rails

MY CODE GOES BELOW:

book = Spreadsheet.open 'excel-file.xls'
sheet = book.worksheet 0
book.write 'output-file.xls'

and here goes the first problem:
I want to remove data that comes after ";" (semicolon) in a column.
Example below.

FULTON BANK NA;FULTON BANK

I just want it to be FULTON BANK NA for example.