Killing weed trees with herbecide...
When the herbicide goes to the roots and also into the ground, as the roots deteriorate, will that make the soil "poisoned" ....???
The most common "systemic" herbicides are glyphosate and triclopyr. If you are referring to glyphosate, it breaks down in the soil and bonds, or adheres, to soil particles. There is controversy about whether this affects the soil. We do not recommend using these herbicides unless other means and methods are ineffective and the situation is urgent. They should not be used casually or excessively.
That said, you can get more specific answers from the National Pesiticide Information Center at 1-800-858-7378.