Laurie from Friday Harbor writes
Helena Crossbow Herbicide cannot be used in septic systems or in or around any body of water. We are unsure if spraying the product on the foliage of the plant above ground directly would cause any issues with the tank. We do carry a product called Hi Yield Root Killer that is made for killing the roots of plants that have infiltrated the lines of the septic system, and may work to help eliminate the blackberry bush you have. We would recommend speaking to someone locally perhaps to see if there are any products the city uses currently for situations like this.
Answer last updated on: 07/03/2022
