Of those listed in Schedule 9, the most commonly encountered species are Japanese knotweed, Himalayan balsam and Giant hogweed.
Japanese knotweed (Fallopia japonica) is a fast-growing and strong clump-forming perennial, with tall, dense annual stems. In early summer the bamboo-like stems emerge from rhizomes deep underground, shooting up to over 2 metres and suppressing all other plant growth. Capable of growing up to 10 cm in a day, Japanese knotweed out competes most of the native vegetation found in the UK today. It forms thick, dense stands that cast shade on the area below, limiting the growth of other species and seriously reducing local biodiversity. These thick stands can reduce the capacity of channels to carry flood water, causing upstream flooding. When the stands die back in winter, the river bank is then exposed to erosion.
Japanese knotweed can seriously damage buildings, hard surfaces and infrastructure. The underground structure of rhizomes slowly expand, exploiting any cracks or voids. Once established, it can be very hard to control and will exacerbate any existing weakness in structures, such as drains or patios. Its presence on development land causes economic loss to the construction sector, primarily through the cost of control and eradication.
When Japanese knotweed is present on development sites it causes significant and costly delays to homebuilders. For domestic properties, its presence can result in the refusal of mortgages or building insurance by lenders, delay or prevent the sale of a property, and even reduce the property’s value.
Sadly, Japanese knotweed cannot be ignored or left untreated. Due to the speed and ferocity of its growth, it will only become more difficult to treat and incur more expensive removal costs. Not with-standing the potential structural and financial implications, there are laws that must be adhered to regarding what you must, can and cannot do with Japanese knotweed.