Tordon tree killing question

[alteran]

I am killing 4 mature spruce trees with Tordon. Drilled holes around the trunk and into exposed roots last august and put Tordon in the holes. Its working but very slowly.
If I repeat the application now in winter will it be effective or does the tree need to be actively growing? I'd like them to be dead and brown by May.
I'm in northern Wisconsin.

Thanks!

 

[Kneejerk Bombas]

Why are you doing this?

 

[alteran]

The trees are growing over the 30 year old steel septic tank and drainfield at my second home where my mother lives.
I want the trees gone so when the septic fails in the next year or so I don't have to do a tree removal project at short notice so the plumber can replace the tank.
My mother is elderly and will have a fit if I cut the nice trees even though they have to go. She is a gardener however and understands removing dead plants. So...... I am making the plants dead.

No there is not another place the septic can go. No, she will not listen to reason. Yes I have tried to think of any other alternative.

Unfortunately sometimes you just gotta do what you gotta do.