Re: black soot on lemon leaves

Barbara:

I have the same problem on a Washington Navel Orange.  I believe it is a 
sooty mold (actually a fungus?) that is associated with the presence of 
honeydew secreted by scale insects.  I think if you look closely, you will 
find scale insects lining small branches and the central veins of some 
leaves..  The sooty mold will spread to areas that don't have the insects, 
but in my experience, it is always associated with either aphis or scale 
insects.  Some control of the insects can be had by repeated spraying with a 
light horticultural oil.  The sooty mold would probably require a fungicide.

Kurt Mize
Stockton, California
USDA Zone 9
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