The preferred treatment method is a herbicide treatment. From this, we would recommend to spray the Japanese knotweed when the plant is actively growing. Which is typically from April-October. Our herbicide that we use is a systemic translocating herbicide. As well as this, the herbicide treatment is most efficient on a warm, day. We use a variety of chemicals to treat Japanese knotweed. But this one is significantly stronger than what is available to the general public and one is not available to the public in any form.