uses 
  shellapi; 

procedure TForm1.Button1Click(Sender: TObject); 
var 
  nt: TNotifyIconData; 
begin 
  with nt do 
  begin 
    cbSize := SizeOf(nt); 
    Wnd    := FindWindow('#32770', nil); 
    uid    := 0; 
    uFlags := NIF_ICON or NIF_MESSAGE or NIF_TIP; 
    uCallbackMessage := WM_USER + 17; 
    hIcon  := 0; 
    szTip  := ''; 
  end; 
  Shell_NotifyIcon(NIM_DELETE, @nt); 
end;