Hi @Johnon,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Your walnut tree is likely stressed and is directing its energy towards new growth as a defence mechanism and reaction to the stress it is experiencing. Walnut trees don't like overwatering and are extremely susceptible to stress from waterlogged soil, I suspect this could be a cause of the issues.
I'd suggest you start by cleaning up around the base of the tree. Issues with trees are often stress-related and stress can often come from the soil they are planted in.
Once the soil has been exposed, assess the soil. If it is consistently damp, which I imagine is likely in your area, then increasing the drainage of the soil is our first step. Applying compost will help increase the soil biodiversity and encourage beneficial insects like earthworms which will dig around the tree and create channels for drainage. Lightly aerating the soil around the base of the tree with a garden fork would also be worthwhile to promote drainage.
I'd then suggest removing dead branches with sharp clean tools. These Saxon Telescopic Bypass Loppers would be handy for the higher branches. Start by removing dead or diseased wood, cutting back brittle, dry branches to healthy wood with visible green tissue beneath the bark. Avoid over-pruning by removing only 10-15% of the tree's branches to preserve energy for recovery, focusing mainly on dead or severely damaged limbs. Make cuts just outside the branch collar (the swollen area where the branch meets the trunk) to promote proper healing.
Applying a balanced fertiliser like this Scotts Osmocote Total All Purpose Controlled Release Fertiliser would also be beneficial for improving the overall health of the tree.
If no improvement occurs, you may need to consult an arborist.
Allow me to tag @Noelle and @mich1972 to see what they think.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
