Question
QUESTION: I have a lemon tree in my front yard for about 5 years now, I dont know how old it was when we bought it. Sacramento, Ca is the location. For about a year now the tree is not looking good. Its providing a lot of lemons and they taste great, but the leaves itself and lemons do not look good. ALL of the leaves and lemons contain a black substance that looks as if it was sprayed on. It looks like dried oil or something of the sort..it comes off the leaves easily, but to wash it off the lemons I have to use a sponge with soap. Its a black residue. And on the lemons its always worse at the top and looks as if it drips down the lemon. Other than that the tree looks absolutely healthy with no holes in the leaves or cracks in the lemons. Please help! We use compost from a nearby farm for the soil. I also have citrus trees in my backyard, and they are doing great and show no symptoms of this at all. And I believe I am caring for all of them them the same way. Again, Please help by giving me possible reasons and solutions!
ANSWER: Alina,

The black substance is called sooty mold. This is a fungus that is grows on a sugery substance, called honydew. Honeydew is the excrement of aphids. Check the undersides of the leaves and branches for the aphids and treat them with a horticultural soap or oil.

Good luck,
Ed Gulliksen

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

QUESTION: Thanks for your reply first of all. Next, where do I get this horticultural soap or oil? And how do I treat the aphids? The tree is big and I dont really understand how I can use the soap on it..please explain. Thank you so much!

Answer
Alina,

Horticultural soap is sold at local nurseries or garden centers. It is mixed with water, as per label directions, and sprayed out of a sprayer. If the tree is too big, I would recommend contacting a local tree spraying company to take care of the problem.

Good luck,
Ed Gulliksen