How to treat brown patchy plane tree leaves?

[OranaGardener]

Hello, can anyone help me to identify what is happening to my sycamore/plane tree, please? It is four years old and each year in Spring the leaves have this problem. Each year it has progressively become worse and this year all the leaves are covered with it. I don't think it is any of the usual culprits like scale, a fungus, etc. My neighbour has the same tree but an older, larger one, which grows very close to mine and their's has never had it, so I don't think spores are blowing around. I think my tree could eventually give up if the problem isn't appropriately dealt with. Could it be too wet?

 

 

 

 

[MitchellMc]

Hi @OranaGardener,

What you’re seeing is more consistent with a physiological or environmental issue rather than a pest infestation. In plane and sycamore trees, this kind of red or purple mottling on the underside of leaves is often linked to root stress, poor drainage, or waterlogging; all of which interfere with nutrient uptake. When roots are stressed, the tree struggles to absorb nutrients like phosphorus, magnesium, or iron, leading to discolouration that can look almost vein-deep. Given that your tree is four years old and planted near another healthy one, subtle site differences (like a compacted or wetter patch of soil) could easily explain why only yours is affected.

To check this, gently dig around the base of your tree about 15–20 cm deep and feel the soil. If it’s consistently damp or smells sour, it’s likely too wet or poorly aerated, which can cause chronic root stress. Improving drainage by lightly aerating the soil around the root zone and mulching (while keeping mulch away from the trunk) can help. If watering is frequent, try easing back.

Less commonly, similar symptoms can appear due to micronutrient deficiency, especially if the soil is alkaline. A slow-release fertiliser with trace elements, such as one formulated for ornamental trees, can help restore balance.

Would you happen to know if the area tends to hold water after rain, or if the tree is in a lower spot compared with your neighbour’s? That could confirm it. 

Let me tag @Noelle to see if she has any thoughts.

Please let me know if you have any questions.

Mitchell

[Noelle]

jI @OranaGardener 

In my opinion, it's not a disease or insect problem but rather, as Mitchell has already suggested, a soil-related issue.

Checking soil moisture, and then either reducing watering or improving aeration if it's very damp, and attending to feeding are the easiest and most obvious starting points. Adding fertiliser and not over-watering are not likely to cause major improvements to the appearance of the leaves this year, but should certainly have some impact next year.

[OranaGardener]

Thank you Mitchell, I believe you're spot on! I lost five 4-7 year-old trees this winter, from stagnant, standing water in my back garden. Albany City Council is doing a terrible job of drainage in Orana. I actually had algae growing all over my lawn for weeks, after the water finally went down.

I have noticed that a number of my European trees have done very well in the boggy conditions, most particularly the Ashes and pear trees, so I wasn't sure if it was the standing water that was affecting the plane tree but I did suspect it. I've lost a number of native shrubs, also. It was a particularly wet winter - I'm hoping we don't have a similar one for a long time! I'm trying to find larger-sized paperbarks for sale but haven't sourced any yet. 

I'll follow your suggestions regarding feeding and soil aeration etc. Thank you again, for your speedy and knowledgeable reply. 

[OranaGardener]

Thank you for your help, Noelle.