Applied Chemistry

To combat roots, cities can implement a preventive maintenance program using the following chemical herbicides that kill the roots without harming trees:

  • Copper sulfate. This is fast and economical, but toxic to aquatic organisms. The crystals can be poured into the sewer line, where they dissolve and are carried by the flow. Copper sulfate may not reach roots that have invaded through the top of the pipe.
  • Dichlobenil. Mixed with a foaming agent that fills the pipe, dichlobenil reaches roots at the top of the pipe. It can be poured into the line or applied using a jetter, killing roots on contact at low concentrations (about 100 ppm). It is not toxic to birds, fish, aquatic organisms, or treatment plant biology.
  • Diquat dibromide. Mixed with foam, diquat dibromide is a desiccant, killing roots quickly by drying them out. However, it relies on light and photosynthesis, rarely present in sewers, for optimum effectiveness.
  • Metam sodium. Applied using special foam equipment, metam sodium kills roots on contact. The EPA classifies it as a 'Restricted Use' product, which requires a license to use.
  • Sodium hydroxide. Sodium hydroxide generates heat on contact with roots, oxidizing and decomposing them. Carried by the flow, it may not reach roots at the top of the pipe. It is highly caustic and must be handled with extreme care.

FROG is a persistent foe, but with an arsenal of solutions at their disposal and a good plan of attack, municipalities can prevent sewer backups and reduce operating costs. Seek solutions that complement each other, that don't harm pipes, and are not caustic.

Jarrett Jackson works for RootX, Salem, Oregon.