Yes, performance testing can be done manually. According to my experience I am using the Page Load time extension of googlge chrome and measure the page load time and benchmark it. During Beta phase, the application is really in the production envirnoment. Now you need a tool to trace the performance and compare it with the benchmark value.
But every application does not go through Beta testing. Hence automation and performan tool / test suite is the best way to test the performance before the application goes in to the production envirnoment.