June 18 (Reuters) - Canada’s main stock index fell at the open and was set to mark its worst day in more than two weeks on Friday, dragged by energy stocks as crude prices dropped for a second straight day. * At 9:30 a.m. ET (1330 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 119.16 points, or 0.59%, at 20,024.88. Reporting by Amal S in Bengaluru; Editing by Ramakrishnan M. Our Standards: The Thomson Reuters Trust Principles.