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The Removal of Tree Roots in Sewers With Herbicides

roots image by cassiusjb from

Trees and woody shrubs that have tap roots are most often responsible for blocking sewer lines. Lateral roots growing from the tap roots pursue water leaking from joints and cracks in sewer lines. Roots may sometimes be removed with mechanical devices that use rotating augers or blades or blast the roots with water under pressure, but controlling them with herbicides is usually the most efficient and dependable.

Types of Herbicides

Roots and foliage absorb systemic herbicides and carry them throughout the plant. These herbicides kill plants above ground and should not be used to clear roots from sewer lines. Quick-acting contact herbicides kill only that part of the plant that they physically touch; contact herbicides are used for cleaning roots from sewer lines.

Formulation Types

Wettable powders are mixed with water and flushed into sewer lines. Wettable powders come in 50W (weight) and 85W. The lighter 50W remains suspended in the sewer for a longer time. Foams require special equipment to produce and pump into the interior of sewer lines. When 1 gallon of chemical-water solution produces 14 gallons of foam, it is called wet foam. When 1 gallon of solution produces 20 gallons of foam, it is called dry foam.

Copper-Based Herbicides

Commercial herbicides containing copper sulfate have long been flushed into sewage lines to clear roots. However, plant scientists at the University of California, Davis, say that excessive amounts of copper sulfate can kill trees and other above-ground plants in addition to microbes necessary to treat sewage. California bans the use of copper compounds to remove roots.

Herbicides Available Commercially

Sodium hydroxide combined with 2,6-dichlorobenzonitrile, also called dichlobenil, is an effective herbicidal mix to remove roots. Sodium hydroxide liquefies grease and soap that combine with masses of roots to block sewer lines. Dichlobenil destroys tree roots and suppressed their regrowth; it blocks the regrowth of roots by condensing on the surface of clay and organic material. This herbicide, approved by the EPA, is available to consumers in form of a wettable powder that is mixed water and pumped into the sewer line.

Herbicides Applied Professionally

Products containing metam-sodium are contact herbicides that break down into methyl isothiocyanate (MITC) that kills plant roots. Metam-sodium is combined with dichlobenil. A hose is pushed into the sewer line. As the hose is retracted, it pumps herbicidal foam containing metam-sodium and dichlobenil into a sewer line. The foam, which kills roots in hours, is washed away with the sewage. Bacteria and other microorganisms take several months to a year to decompose the dead roots. Metam-sodium herbicides can only be applied by licensed professionals and the sewer line may need to be treated again in three years for persistent roots.

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