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Will Roundup kill my trees?

As an ISA Certified Arborist I get to look at a lot of trees and how they are affected. Many times I hear clients asking Will Roundup kill my trees? or, “Will weed killer kill my trees?”

There’s been a few times in my career since 1997 that I’ve seen clear evidence of weed killer killing trees. This was one of them from last week.

Basically, my client had used “Roundup Extended”, or “Roundup X” along his path at the base of the tree. He had used it liberally within at least half or more of the tree’s critical root zone.

The client had called me to ask what was going wrong with his tree as it was not thriving as it had in years past. He had never used round of tax prior to this past season.

The thing that was so striking about this example was the pattern of die out in relation to the path. Basically, he sprayed the path in between the tree and the house. Typically speaking right side roots feed right side branches and left side roots feed left side branches. Looking at the die-out pattern of this tree, the only place that did not look affected was the section directly over the grass but did not get sprayed.

Mode of action
The way that weed killer enters planty material is called “mode of action”. Certain chemicals are uptaken within the roots, others can soak in through the bark, others have to be injected directly into the tree system, and others enter in by just touching the leaves of the tree or plant.

Roundup’s mode of action is supposed to be through the leaves. There is a possibility that the roots of this tree grew small suckers which the client sprayed with Roundup and the tree took in the chemical that way. However, there is also a possibility that the tree took in the chemical through the root system or by directly spraying it on the trunk.

In some of my continuing education classes I have heard discussions of different cases where Roundup extended, or Roundup x, and the specific chemicals within this product vs normal Roundup, are affecting trees in a negative way.

My suggestion is not to use Roundup X. After hearing different arborist discuss different examples of this specific product killing trees, I think it would be more prudent to use a different product.

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