By Gardener55
United Kingdom 
What are these strange lumps on my young apple tree trunk?
So this tree is an apple sapling that was grown from seed. It started developing these lumps near where the branches grow from the trunk last year. It is not on any of last year’s growth, but only on the year before’s growth. I think they started developing after I repotted it last year. The tree didn’t stop growing until October last year, and it didn’t shed its leaves until December.
26 Feb, 2025
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There are various causes of lesions on young apple trees like this. The most serious is Fireblight. You would see this later when the leaves appear, blackened and looking as if they have been scorched. If that happens then destroy the tree before it spreads to any other trees.
OR. It could be insect damage. There are plenty of wood boring insects which cause the tree to protect itself by developing these scars. There is usually sawdust either down the trunk or on the surrounding soil, if it is an insect.
Finally there is mechanical damage. Something may have knocked off baby branches and this is the trees way of protecting the wound.
27 Feb, 2025