frankrichards16 said: I might have to try tordon, looks effective.
Tordon quickly, IF, you put a cut into the tree bark and apply it to that cut.
With the number of trees you have, labor intensive.
I have dispatched trees 4 ft. tall by spraying brush killer on the leaves; best if done twice.
You could just cut the tree off waist high and brush/spray the cut trunk.
I once replanted a garden , guessing, 12 by 8 after digging up a huge number of trees, some six feet high, buckthorn and poplar.
I then took a clippers and cut them down to 4 to 6 inch twigs and put them in a 70 gallon portable refuse bin.
Filled that sucker to the point the lid just barely shut.
It had been my grandfather's garden but after he died some medical situation go to my aunt, who had been a gung-ho gardener and it, and her flower gardens sat untouched for 10 years.
Amazing how trees can take over.