Question
QUESTION: I have an older lemon tree that is developing white patches on its bark.  Is this a disease and is there a treatment for it?
ANSWER: Terry,  

I am out of town, and I will answer your question soon.

Hi Terry,

Could you be a bit more descriptive?  Are the white patches fuzzy?  Do they have discrete margins, are they clearly defined?  Are these areas raised from the surrounding stem tissue?  Provide as much information as possible.  

Thanks.

---------- FOLLOW-UP ----------

QUESTION: Hi Jim,

The white patches are mostly circular, although in places where they are larger the shape is irregular.  They have discrete margins.  They are slightly raised from the surrounding tissue, as I can scape them off with my fingernail, but when I do, I also remove a bit of the bark.  They are not noticably fuzzy, as they are quite close to the surrounding bark.  The tree is located on the central coast of california where we have a moderate climate with dew in the mornings.  

Thank you for your help.

Teresa

Answer
Hi Terry/Teresa,

I will have to do some more research on this one.  My first thought was citrus canker, but that is not a disease common to California.  If you have a magnifying glass, examine the lesions very carefully to see if these fuzzy lesions show any details.  This may be an opportunistic fungus that may not be harmful at all.  Without pictures or more details, I cannot easily determine what it is.  However, if there are fuzzy anatomical features, discrete margins, and are elevated above the stem, these are certain indications of fungal growth.  

I don't know of any way to send photos via this expert forum, but I will try to find out if it is possible.