- Dec 23, 2015
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I didn't know that. So I Googled it. Well, it turns out that RoundUp can, and will, effectively kill a plant via root absorption.
Here's the text I got from The Effect of Glyphosate on Tree Roots :
Glyphosate
Glyphosate is an organic, high-phosphate compound widely used as a broad-spectrum herbicide to kill unwanted plants of many different types. It is usually diluted in liquid and applied as a spray directly on the weeds' foliage. When it contacts a plant, the compound is taken up by its roots and foliage, where it blocks an enzyme required for plant survival, eventually causing it to die. During spraying, glyphosate also comes into contact with soil. It binds strongly to soil particles and can remain in the ground for many months, according to Cornell University.
Tree Roots
Roots serve many roles in supporting all plant life, including trees. They take up water and nutrients from the soil, allowing them to move into and through a tree's transport system to reach all of its parts. According to Utah State University, when glyphosate is applied to an undesirable plant and kills it, the dying plant releases some of the chemical back into the soil through its roots. Tree roots in the area can take up some of this chemical, either by contact with the roots of the dying plant or by directly taking up residual glyphosate from the soil.
I am not an expert on herbicides, but glyphosate is not considered soil active. As noted it may bind to soil but that does not make it "available" to plant roots - it is bound to the soil. Some direct root contact may allow uptake prior to binding with soil. The big but here is labeling - it is not labelled to be used in this manner, and it is therefore actually illegal to use it against the label. Especially important for restricted use formulations.