Comments PLugin Issue

I am using a review site plugin, this code is added to comments.php to show the review fields:

<?php echo dgrs_get_rating_fields(); ?>

However I do not want this review code to show on pages, only on posts, but I do want comments on pages.

How can I get the review code only to show on posts?

I tried this in my comments.php and nothing showed up then:

<?php if (is_category()) {
echo dgrs_get_rating_fields();
}
?>

Any ideas?

Thanks.