Japanese knotweed is a large herbaceous perennial plant, that is native to eastern Asia in Japan, China, and Korea. It was brought to the United States as an ornamental about 75 years ago, and has spread like wildfire all across the USA. In North America and Europe knotweed is very successful and has been classified as one of the top 100 invasive species in the world. Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not closely related. The invasive root system and strong growth can damage concrete foundations, buildings, roads, and asphalt paving. Knotweed will tolerate a wide range of soil types, pH and salinity. Its roots can survive temperatures of -30F, and can extend over 20 feet horizontally and 10 feet deep, making removal by excavation very difficult. Herbicides are the only real control method, and treatment along streams is difficult. Once the plant is established in an area, eradication is almost impossible. It will grow back from the roots, seeds in the soil, and from small pieces of plants left behind during the removal process. I've made multiple applications of Roundup herbicide to the knotweed growing next to the walk bridge, along the creek on the 7th hole. The herbicide will knock it down for a while, but it keeps coming back as if no application was ever made. The only way to get rid of it is to spray it with Roundup, remove the dead plants, excavate as many roots as possible, and plant something else in it's place. During the next several years while the new plants are getting established, you have to go back and remove the knotweed sprouts by hand. Once the new plants are established, the knotweed will not grow back since it does not like shade. The photo below is of an area along the stream on #16, where the knotweed was removed and other plants were planted four years ago.
Look closely, and you can see on the left where the knotweed stops and the native plants start. We planted Red and Yellow Twig Dogwood, Red Flowering Currant, and Salmonberry. These plants thrive close to the stream and are aggressive growers, and within three years are big enough to displace the knotweed.
This is a shot of the 8th tee from the fairway side of the creek. We can continually knock down the blackberry and knotweed, but this is the best it will ever look until we plant some natives to replace what's there now.
This is the view of the stream at 8th tee taken from the bridge. The knotweed is knocked down on the tee side, but the fairway side is growing like crazy. (Special thanks to Joel on our crew who maintains this area. He spends a lot of time keeping the weeds knocked down, and hauling away the remains. It's also very difficult to work on that slope without falling in the water!)
This is at the walk bridge to the 8th tee, on the #7 side. The native plants on the left are keeping the knotweed out, but where they stop, the knotweed thrives. We can remove and replace the knotweed with native plants, but it will be a long and costly process. I think it's a project worth doing, even if we chip away at it, one section at a time.
