Feb 23 (Reuters) - Wall Street’s main indexes opened lower on Tuesday as investors sold off high-flying growth stocks on valuation concerns ahead of Federal Reserve Chairman Jerome Powell’s testimony before Congress. The Dow Jones Industrial Average fell 19.8 points, or 0.06%, at the open to 31501.89. The S&P 500 fell 19.4 points, or 0.50%, to 3857.07, while the Nasdaq Composite dropped 270.4 points, or 2.00%, to 13262.607 at the opening bell. (Reporting by Devik Jain in Bengaluru; Editing by Shinjini Ganguli)