Only show post from specific category (by name), but not from subcategory

Hello there,

I’ve got an issue with getting posts from a specific category, without getting posts from its subcategory.

—

I’ve got a sidebar that only shows a post regarding to an event. In fact, it only shows the last post of a category (named “competition”), as the other posts from that category are automatically closed at a defined time.
By “closed” I mean that they are moved into another category which is a child of the main category “competition”. Subcategory is name “closed”, in this example.

So, I would like to only show the last article from a category, but not the articles from the subcategory.

I would also like to work with categor_name, not ID.

Here is the code which is currently working for the parent category, but still shows posts from the children (or sub-) category.

<?php
                query_posts('category_name=competition,-closed');
                if (have_posts()) :
                    $count = 0;
                    while (have_posts()) :
                        the_post();
                        $count++;
                        if ($count <= 1) :
            ?><div id="giveAway" class="sidebar shadow">

                <a href="<?php the_permalink(); ?>">
                    <div class="title">
                        <h2>Competition<img src="<?php bloginfo("stylesheet_directory"); ?>/design/iconLink.png" /></h2>
                    </div>
                    <div class="content">
                        <?php
                            MultiPostThumbnails::the_post_thumbnail(get_post_type(), 'secondary-image');
                        ?>
                    </div>
                </a>                

            </div><?php
                    endif;
                    endwhile;
                    endif;
            ?>

I thought that the “query_posts(‘category_name=competition,-closed’)” code would exclude the subcategory from the query, but it seems not to work.

Is there any work around?

Séane