postgis - QGIS DB manager Import layer/file tool won't allow me to choose "Append data to table"

I want to append some data to a layer in my PostGIS DB using a shapefile, but when I use the Import layer/file tool in QGIS, it doesn't allow me to choose the append option. Why is this and how do I get it to allow me to append?

Answer

Same problem goes for me with the DB manager in QGIS - Append not available.

But it is pretty stright forward in pgAdmin III with the plugin 'PostGIS Shapefile Import/Export Manager'.

Be sure to set Mode to Append, SRID, Table name to name of table to append to. Also in Import Options disable 'Create spatial index automatically after load'.