n3k4

To help your WordPress installation be more optimized for search engines, this plugin will include a ‘noindex’ meta tag in the header of any duplicate posts. 
Robots will not index any posts with matching title tags, which is a known indicator of negative SEO. This is very useful for automated posting and working with a large amount of posts.

Noindex Duplicate Posts

This plugin will automatically add a 'Noindex' meta tag to posts that are a duplicate determined by the slug and preexisting post names.

amodoke

This plugin lets you Noindex Nofollow All Posts in a category. 
Simply go to Posts > Categories, and click on any category’s EDIT link. 
There you can just “tick” the relevant option you need. 
The plugin will then add a “noindex” or/and “nofollow” line in all posts in that category.
A few notes about the sections above:
<ul>
<li>DigitalChef.in – Madhu Ramrakhyani</li>
<li>This plugin lets you Noindex Nofollow All Posts in a category.</li>
<li>“3.0” is the lowest version that the plugin will work on</li>
<li>“4.7” is the highest version that you’ve successfully used to test the plugin. Note that it might work on 
higher versions… this is just the highest one you’ve verified.</li>
</ul>

NoIndex NoFollow  All Posts

This plugin lets you Noindex Nofollow All Posts in a category.

Noindex Duplicate Posts vs NoIndex NoFollow All Posts