Can't delete cookies

Can anyone fathom out why I can't get the setcookie function to delete a cookie? I'm calling it with the same arguments as I used to set it originally, but with a null string value & an expiry time in the past but the cookie persistently remains in the browser. This how I set it: setcookie ("hhubpassword", md5($newpassword) , time() + 1209600, "/xchange/"); And this is how I'm trying to delete it: setcookie ("hhubpassword", "", time() -3600, "/xchange/"); Thanks Andrew