Posted: 14/06/2016 at 14:30
If a tree that's been in place for 6 years is wobbly it's in trouble. Roots should be below soil, you shouldn't be able to see them through a weed barrier.
If you have any birds in your garden they would prefer their caterpillars not to be doused in insecticide sprays. Just pick them off and throw them down for the birds.
I think you'd be better removing the tree and starting again. I wouldn't use a weed barrier