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What is the blackness on the wall behind the tree. Is it rats or possums. How far should I prune it back further to save it
Hello @70rob
Based on the images you’ve shared, your espalier lemon tree is experiencing significant stress from multiple sources, and it’s great that you're intervening early. The blackness on the wall behind the tree appears to be from a combination of plant sap stains and potentially animal activity. The presence of dark streaks and residue near climbing limbs suggests the possibility of possum traffic, especially since possums tend to use familiar routes and often leave greasy marks along surfaces they repeatedly walk.
However, rodents like rats can also climb trees and walls, and their movement can result in similar patterns, particularly if there’s evidence of chewed bark or hollowed branches, which is visible in your second and third photos. The cracking and stripping of bark, especially around the upper branches, indicate a level of sustained physical damage that’s likely being exacerbated by wildlife.
To save your espalier lemon tree, you will need to conduct a fairly aggressive prune. From the fourth image, it’s evident that several limbs are dry, split, and no longer productive. Any limb with peeling bark, visible rot, hollow cavities, or no signs of new growth should be pruned back to healthy green wood. Make clean cuts using sharp secateurs or a pruning saw and follow the branch back to just above a bud junction or a node from which healthy shoots are still emerging.
If you’re uncertain, a quick scrape of the bark should reveal either green moist tissue (which means the branch is still viable) or dry, brown inner wood (which means it’s not). You may need to remove as much as one third of the tree if the damage is widespread, but it is better to prune decisively and allow the plant to regenerate than to leave infected or dead wood that can harbour pests or disease.
For treatment and protection, I recommend applying Steri-Prune 250g Pruning Spray Paint immediately after cutting to protect open wounds from fungal infections and insect invasion. To deter possums or rats, consider using the Multicrop 400g Scat Bird And Animal Repellent. Additionally, installing Jack 600mm Pest Fence Spike around the main stem can reduce access. To encourage healthy regrowth, feed your lemon tree with a product like PowerFeed Citrus & Fruit, and water deeply but less frequently to reduce stress while it recovers. Mulch around the base with a thin layer of sugarcane mulch to retain moisture and suppress weeds but keep it away from direct contact with the trunk.
By removing all dead and compromised branches, sealing the wounds, and deterring further animal damage, you should see new healthy shoots within the coming season. Stay consistent with feeding and inspect for signs of chewing or nighttime animal activity to stay ahead of future issues.
If you need further assistance, please let us know.
Eric
