$args = array(
'post_type' => 'tribe_events',
'publish_status' => 'published',
);
function xxx_order_events( $query ){
$query->set( 'orderby', 'meta_value' );
$query->set( 'meta_key', '_EventStartDate' );
$query->set( 'order', 'ASC' );
return $query;
}
add_filter( 'pre_get_posts', 'xxx_order_events', 99 );
$var = new WP_Query($args);