"Doug" wrote in newscuai71bka86b3vmalnq8okhg5160t7d1b@
4ax.com:

Google this but years ago I read to drill deep holes and fill with
salt. I don't know personally if this works.

I do. Worked just fine for me about six years ago to kill a mulberry, after numerous other treatments had
failed. However, it wasn't anywhere nearly as large as the OP's acacia (only about 3" diameter, not
16").