How to treat lemon tree with brown spots?

[Sam_Cur]

Hello! We inherited this beautiful lemon tree in our property but noticed these brown spots on some of the lemons and some of the leaves? Is this a fungus? How can we fix it? 

[JacobZ]

Hi @Sam_Cur,

Welcome to the Bunnings Workshop community, it is wonderful to have you with us and many thanks for your question about your lemon tree.

I don't think you are dealing with a fungal issue; it appears to be insect related. 

These bumps on the leaves are likely caused by scale insects. Scale insects are tiny sap-sucking pests that attach themselves to leaves, stems, and sometimes fruit. They look like small bumps or shells stuck to the plant surface. They don’t tend to move around much because they cover themselves with a hard, waxy coating for protection. They’re common on citrus, but manageable. I'd suggest applying Seasol EarthCare White Oil Insect Spray to any leaves or fruit where you see them. It can be applied to the fruit, but if you plan on eating it, I would give it a good wash beforehand.

Then there are these holes in the branch, which are likely caused by a different insect, potentially gall wasps or borers.

If you could take some closer photos of this branch and inspect the tree for others, this would certainly help us better understand what you are dealing with.

Based on what I can see, your lemon tree is going to be quite sickly at this point. It is going to be attempting to fight back against the attack, so it would greatly benefit from a good trim to remove any sickly-looking branches or leaves and an application of fertiliser. I'd suggest this Scotts Osmocote Citrus and Fruit Controlled Release Fertiliser is a good option.

I'd also suggest giving your tree plenty of water to help it fight back.

Allow me to tag our knowledgable gardeners @Noelle, @mich1972 and @robchin to see what they think.

Jacob

[Sam_Cur]

Hi Jacob,

Thank you so much for your advice, it’s very helpful! Our poor tree’s under a lot of stress it sounds like. I’ll take your advice and do what you’ve suggested! 

Here are some additional close up pictures of the branches - a lot of them have these clusters of holes. 

 

 

[JacobZ]

Hi @Sam_Cur,

They are almost certainly caused by citrus gall wasps.

Citrus gall wasps are tiny black insects that lay their eggs inside the stems of citrus trees, most often lemons. The tree reacts to the larvae feeding by forming swollen, woody lumps called galls. These galls weaken the tree by reducing nutrient flow, stunting growth, and lowering fruit production if left untreated.

Have a look at How to control citrus gall wasp and How do you remove gall wasp from a lemon tree?

After reading these articles, let me know if you have any questions.

Jacob