Homeowners beware: Japanese Knotweed can take over your property and it is not an easy kill. Knotweed, an invasive plant on the west coast, looks like bamboo, can grow to be six to 10-feet tall and completely dominates the environment in which it lives. 

“If it’s growing, it’s usually a forest. It really takes over streambanks,” Brad Mead, the Invasive Species Coordinator for Clark Public Utilities said. “Any area that is where the water can go, knotweed will spread to those places and completely take it over, even pushing out trees and everything else.”

In the United Kingdom, banks can refuse to mortgage a property that shows signs of knotweed infestation. The plant can push up through foundations of houses and crack the concrete. 

As a precaution, CPU is coming out to properties around the area and providing free herbicide treatment on the plants and properties to prevent the spread of knotweed. 

“CPU really needs everyone’s help to allow them to come out and survey so they can get to every single plant,” Mead said. 

Knotweed starts coming up in the soil around the end of April, keeps growing until it hits full height in June and then flowers in August. CPU typically does a treatment before the flowering and after the flowering, to avoid any possible harm to bees as they pollinate the plants. 

Mead warns homeowners that herbicides from a licensed contractor are the only way to stop a knotweed infestation due to its ability to spread through fragmentation.

“Any piece of the plant that’s more than half an inch long can create a new plant. So if a beaver gets in there or if somebody were to weed whack though there,’ Mead said. “Don’t cut it or compost it or do any type of tilling activity. Any type of disturbance will just move it around more and help the plant out.”

A typical knotweed infestation takes years to eradicate. According to Mead, to get rid of knotweed, the PUD would need to do five years of extermination work followed by five more years of monitoring. 

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