To Delete a Manure Prohibited Area, click on Drawing Tools | Delete Features | Manure Prohibited Areas.  A Delete Manure Prohibited Area box will pop up. Click on the manure prohibited area(s) you would like to delete. Once all are selected in yellow click Delete Manure Prohibited areas

A box will pop up asking if you're sure you want to delete this manure prohibited area. Click OK. The manure prohibited area(s) selected should now be removed from the map.