My mums partner has said about this before, he used rusty copper nails and just hammered a few in the middle of the stumps.

Are you sure they were copper and not iron nails? Just that copper doesn't rust.

That's what he said. *don't shoot the messenger*

They will be copper, Myron - copper kills plants, but it takes ages.

Steragram, can you not drill into the stumps and apply SBK?

Ive killed a very large willow stump by drilling holes into it and then adding a glyphosate based herbicide but mixed 50/50 with water, so very strong mix.

Do it every day for a week and see what happens.

I've also heard that old engine oil works, but I would think that this isn't good for the environment as it would probably seep into the ground.

Hi, I have killed a large ash, and a very large sycamore, by using a 2 stroke mixture, just brush it on and leave it, the bark will start to rot off after a few months, which will tell you that the trunk is dead, it will take a ew years for the trunk to rot, but at least it won't send up any suckers, it won't do any damage to the environment, as it will never reach the soil, it just soaks into the stump, so if you can stand to look at the stumps, you could use this method, Derek.

Yes I tried it many years ago but it didn't work and it seemed to make the tree stronger I also tried cutting a ring out of the bark all round and that also didn't work.
So best of luck

I killed an old willow years ago by having holes drilled into trunk, filling with glysophate & covering with black sack to stop it being washed away & to keep wildlife safe.

I say again, SBK brushwood killer, used neat, poured into pre drilled holes. Does the job every time, been using it for years...

Thank you for all your answers!
I should have given more details.

The problem with using chemicals is that some of the trees are not accessible enough and we couldn't reach the cut area well enough to slit round the bark, and certainly wouldn't be able to cover the stumps afterwards - we have used SBK on a couple of others in the garden but the covering blew off one of them and its still sending up suckers all around so that's one problem.

In case you're thinking we are deforesting the planet, the main problem ones are mature wild sycamores on our border which were cut down by BT because of power line interference. There is so much more light on our veg patch that we don't want suckers to grow up to replace them but they are just the other side of our fence and at the top of a high very steep bank, almost vertical. We can't quite reach the cut area from the garden or climb up from the road but we could possibly manage to bang nails in if it would work from the base of the stump. It doesn't matter if it takes a long time to work.