To disable all products from a specific manufacturer, navigate Catalog > Manage Products.
Before you begin searching the products by manufacturer, click Reset Filter to make sure all other search filters are clear.
Select the manufacturer you wish to work with from the drop-down manufacturer list on the catalog page and select Search.
Now that all of the products from that manufacturer have appeared, click Select All on the top left of the product list.
On the top right of the product list, there is a field labeled Actions. Click into the Actions drop-down and select Change Status and click Submit.
After hitting Submit, another drop-down field labeled Status will appear to the right of the Actions drop-down. Click into the drop-down and select the desired status. For this example, we are disabling the products.
After selecting your desired status, hit Submit.
All of the products from the manufacturer you selected should now be disabled.
System > Cache Management
System > Index Management
Reindex if necessary.