// hook into the init action and call create_activity_taxonomies when it fires
add_action( 'init', 'create_event_taxonomies' );
add_filter( 'manage_taxonomies_for_event_columns', 'dates_type_columns' );
function dates_type_columns( $taxonomies ) {
$taxonomies[] = EM_TAXONOMY_CATEGORY;
return $taxonomies;
}