Japanese knotweed is similar to any other weed – it is best treated in late summer and autumn. The reason for this is that as with all perennials they start to absorb nutrients into the rhizomes as such by applying a herbicide at this time of the year it is far more likely to reach deep into the plant and kill the entire plant by applying at this time of the year. However, you can carry an excavation out year-round, if the location of the weed has been established. We will detail the treatment protocol we follow here at Japanese Knotweed Expert below.