Hello Bill:

Our septic guy suggests using Roebic Foaming Root Killer on our system that has severe root intrusion. Both he and the manufacturer state that the product does not harm the tree itself, but just kills the intruding roots and prevents regrowth (when periodically reapplied). What do you think?


This is a subject I have not written about for over seven years, so it is about time to look at it again.

I had to look up this product and check the active ingredient. It is dichlobenil, a chemical I first noticed back in my retail nursery years. It is the active ingredient in certain “pre-emergent” herbicides sold in granular form, for scattering on the soil surface to kill weeds as they sprout from seed.

Here is an excerpt from a Wikipedia article on dichlobenil:

“In 1971 in the U.S. state of California, their department of agriculture reported, ‘Dichlobenil kills the roots of many species, but not all; further, the killing does not extend much beyond the portion actually soaked.’”

In contrast, various other classes of herbicides are translocated through the system to kill the whole plant. Examples include phenoxy herbicides, like Silvex, with the active ingredient, 2-4-5-T. Infamous for its use by the U.S. for deforestation of broadleaf trees during the Vietnam War and used to kill broadleaf trees and plants in forestry, its registration was canceled in 1985 because a contaminant in the formulation causes cancer and birth defects. Other phenoxy herbicides are still on the market.

Glyphosate is another, extremely popular “translocated” herbicide. I have personally sprayed many gallons of it to kill weeds and poison oak. Literature on the product states that it adheres to soil particles, thereby deactivated on contact with soil. But recent news, reporting trace amounts of it in wine, makes me wonder if I have been dismissive as to its potential health and environmental effects.

An article in The New Yorker, April 2015, stated:

“Late last month, the International Agency for Research on Cancer, an arm of the World Health Organization, issued a report that classified glyphosate, the active ingredient in the herbicide Roundup, as a ‘probable’ cause of cancer. Glyphosate is the most heavily used herbicide on earth.”

Those are chemicals no one in their right mind would pour down a drain or into a septic system to control invasive roots. It would be foolhardy, probably ineffective, and totally against label directions.

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As for dichlobenil, formulated for root control in sewer lines, it looks like this foam formulation is safe for trees. It is not a translocated herbicide that kills the whole plant.

Checking a Material Safety Data Sheet (MSDS) on the chemical, I found some cautions: It can contaminate groundwater, and is toxic to fish at a concentration as low as 5 mg/liter.

The MSDS states:

“The use of this chemical in areas where soils are permeable, particularly where the water table is shallow may result in ground-water contamination.”

I am concerned that we, mankind at large, are marinating ourselves and life on the whole planet in chemicals that may have all manner of unintended consequences.

At least, when we have a choice, let’s read and follow labels, and use nontoxic options whenever possible.

Bill Pramuk is a registered consulting arborist. Visit his website, BillPramuk.com. Email questions to info@billpramuk.com, or call him at 707-226-2884.