Question
I have a rosemary plant that was recently transplanted.  It is outside and always has been.  I just noticed a type of leaf spot on it.  The center of the infected area is a bright white.  Around the white part is a dark, almost black area.  It looks similar to grey leaf spot that you would find on St. Augustine grass.  I put some 10-10-10 on it about two weeks ago.  It also may be planted too deep.  I live in South Carolina.  We have had about two frosts since I fertilized the plant, but it really looks like some type of fungus rather than frost damage.  Do you know what types of fungi can attack rosemary, and what type I might have based on my description?

Answer
It does sound like a fungal disease.  Cercospora, Alternaria and Septoria are all possibilities.  Remove infected leaves and destroy them.  You can use a fungicide such as "copper fungicide" or Bordeaux mixture.  You can also mix your own by taking one tablespoon of baking soda, one tablespoon of cooking oil and mixing these in a gallon of water.  Treat the plant every 3-4 days until the new growth appears healthy.  There are not many fungicides labeled for use on herbs.  Good luck.