Custom Post Date Filtered

<?php
function dr_filter_where( $where = '') {
    $days = 28;
    $where .= " AND post_date > '" . date('Y-m-d', strtotime('-' .$days .' days')) . "'";
    return $where;
}
add_filter( 'posts_where', 'dr_filter_where' );

$args = array('post_type' => 'agenda', 'post_status' => 'publish', 'paged' => $paged );
$wp_query= null;
$wp_query = new WP_Query();
$wp_query->query( $args );
remove_filter( 'posts_where', 'dr_filter_where' );
// Output our Query
if ( $wp_query->have_posts() ) :
    while ( $wp_query->have_posts() ) :
    ?>

    <?php
    endwhile;
endif;
?>