Germany coach Joachim Low warned his defenders of the threat of England striker Wayne Rooney ahead of next week's World Cup last 16 clash. The misfiring Rooney has yet to discover his goalscoring touch in South Africa, but Low is aware that the world-class forward could be back in business at any time. "Rooney may not have been a big gun so far but he is always ready to explode," the German manager told FIFA's official site. "He is difficult to mark and control so our defense will need to watch that he doesn't score." England have only scored twice so far in the World Cup, thanks to Steven Gerrard and Jermain Defoe.