Plant Doctor Archive

Fungus on lemon tree

I have a lemon tree and the leaves have a white/black fungus on it. My lemons are not bright yellow, they are brown and look dried up. The skin is very hard. I just bought the property with this tree on it. I water it frequently.

It sounds like your poor lemon tree is suffering at the moment. I think you could have one, some, or all of the following problems:

First, your lemon could have a fungal disease called verrucosis. This in itself is usually not of major concern — it usually causes the formation of brown scabs on the outside of the fruit, but doesn't affect the inside. In serious cases, however, the fruit can become hard and leathery and dry.  Treatment is relatively easy — you spray with copper oxychloride 4 or 5 times a year (following the instructions on the particular brand you buy).

Second, the white "fungus" could actually be a mealy bug infestation. These insects are quite hard to get rid of and do a lot of damage to the host plant. You could try removing them with a cottonbud soaked in methylated spirits. If this is too large a job, then try spraying with orthene or conquerer oil.  If it is in fact a real fungus on the leaves, then the copper oxychloride spray should deal with it.

Another possibility is a lack of nutrients or water. Citrus trees are quite demanding when it comes to food — I suggest you buy a good citrus fertilizer and regularly feed your tree.  Sprinkle the fertilizer around the dripline of the tree, but do not dig it in as lemons have their roots quite close to the surface.  Lemons require a lot of water, especially in late summer, so it is possible the previous owners did not keep the watering regime going while the house was on the market.  Good luck!

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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