Q.i think i have killed my 25 year old monkey puzzle tree :(
Hi i wonder if you could help me please, i have a 25 year old monkey puzzle tree and all around it is small old paving that had dandelions growing up in between them so i used weed killer on them then a few weeks later we had it jet washed now my branches on the tree and the tips on the end are going brown i planted it 25 years ago and it is nearly as big as the house i will be devastated if i cannot save it. Thank you.

There is nothing you can do except wait and see.
You don't state what week killer you used or at what application rate, so there is no way we can provide information on outlook for the tree survival.