Japanese Knotweed - Are you growing it in your garden?
Here are some items gathered from the net that might help identify it and then give you some idea of what to do to control it. The comments are mine.
Japanese Knotweed is a semi-woody perennial. It has been cultivated commonly because of its interesting, fast-growing and hollow, bamboo-like stems that form dense leafy thickets, 1-3 m (3 - 10ft)tall, and its late summer flower clusters.
The stems become tough and woody with age, have ridges and exhibit the characteristic swelling of the nodes and the presence of circling sheaths so it looks like a bamboo. Shoots arise from coarse spreading rhizomes that generally reach lengths as much as 20 m. (60 ft.).
The broadly ovate stalked leaves are attached singly and have blades up to 15 cm. long and about as wide as long. Most commonly they have a flattened base, but this may also be rounded or somewhat heart-shaped, and have a short pointed tip.
Each shrubby clump bears clusters of either male or female flowers from the upper leaf axils. The flowers are small and greenish or white, and although functionally unisexual, each male or female flower possesses the complementary, but vestigial, organs of the other sex. Flowers bloom in August and September, with female flowers producing a small 3-angled, shiny black-brown fruit (achene), if male plants are nearby.
Habitat
In its native habitats in Japan, it occurs on hillsides and mountain slopes in open, sunny sites. It is an important primary colonizer of volcanic slopes where sulphur levels are high and soil pH is low. In general, it is a successional species in its native homeland. In Europe, Japanese Knotweed is found on a variety of soils and pH range from 4.5 - 7.4.
Comment:
(It could be a thought to increase the pH by liming after cutting down and before mulching).
It is most common and vigorous in open moist sites and occurs along river banks, wetlands, roadsides and in a variety of disturbed areas. Although it can colonize open forested sites, it generally does not thrive under the shade of forest canopy. In the UK, its distribution appears to be associated with regions of high precipitation.
Control
When clumps have become sizeable it is likely futile to attempt to dig up plants. Such activity would inevitably result in sections of rhizome being missed and many separate underground fragments being created, each of which would serve to produce a new plant. In addition, the removal of even a single large clump is so highly labour intensive that efforts to remove all underground portions of the plant would likely not be achieved. The extensive digging required to remove all portions of the rootstocks would result in a considerable amount of ground being disturbed and would encourage the development of either missed fragments of rhizome or the growth of other weedy species developing from the soil seed bank or from volunteer weed seeds arriving from nearby sources.
Likely the best means of control for Japanese Knotweed is through repetitive cutting of the stems near the soil surface with the addition of spot application of a systemic biodegradable herbicide like glyphosate (e.g. Roundup, etc.) If no herbicide is applied, the act of cutting the stems near the ground during the early to mid part of the growing season results in depleting the food reserves stored in the rhizomes that are necessary to produce new aerial shoots.
Several cuttings would likely be required during a single season followed by a similar treatment the following and perhaps subsequent years until no new shoots appear. The application of glyphosate by painting the cut stems with the herbicide is likely to be more effective and a more rapid means of eliminating the underground portions of the plant.
Glyphosate can also be sprayed on the entire plant, taking appropriate precautions in applying the herbicide for personal health reasons and also to minimize spraying other desirable plants. Glyphosate is a non-selective herbicide. If plants are sprayed, the best time is late in the year when leaves tend to conduct nutrients to the rhizome as part of the build-up of food reserves to support growth the following year. Such general spraying is not recommended in nature reserves where other species may be impacted and because of the likelihood that repeated applications may be required.
The use of fire has also been suggested as a means of controlling Japanese Knotweed. Fire would have the same impact on the plants as cutting off the shoots, thereby reducing food reserves in the rhizomes. However this method of control may be more difficult to apply safety except in cases of large isolated clumps
Biological control research was initiated about ten years ago to find suitable control agents. It has been suggested that the genetic uniformity of this species makes it a suitable candidate for biological control. No release programme has yet been undertaken.
Another description and probably easier to remember!
JAPANESE KNOTWEED (Polygonatum cuspidatum)
Description:
In the early Spring, Japanese Knotweed looks like an army of nondescript fat, red stalks emerging from the ground. The tough leaves are often too undeveloped to give the beginner much of a clue to the plant's identity. Fortunately, you can use last year's dead plants to give you a positive identification. The new shoots appear to be arising from a bamboo jungle consisting of jointed, hollow, wooden poles up to ten feet tall. Nevertheless, Japanese Knotweed is in the same family as rhubarb and buckwheat, not bamboo.
The mature plant has large, oval leaves with pointed tips and squared-off bases. Its tiny, white flowers, which appear at the end of Summer, are arranged in long, lacy clusters. This plant was brought here from Asia as an ornamental because of its beautiful flowers, and it's been spreading into both wild and cultivated area ever since.
Habitat:
Japanese Knotweed grows in waste places and fields. It tends to displace other plants while it spreads, and it's difficult to eradicate
Season:
You can eat Japanese Knotweed in the early Spring only. Later, it becomes too tough.
Food Uses:
Japanese Knotweed has a tangy, tart flavour similar to rhubarb. The best plants to collect are the stems 6 - 8" tall. Taller stems, up to 1 ft. tall, have a tough rind that you must remove. Smaller plants provide less food. Be sure to discard all leaves, which are too tough to eat. Slice the stems, steam them, or simmer them. They're tangy and tart, with a flavour similar to rhubarb, only better. If they're too strong-tasting for you straight, dilute the tartness by using them as one ingredient out of many in a soup or stew.
Like rhubarb, you can also use the tart flavour of Japanese Knotweed to offset the sweetness of fruits in jams or dessert dishes. Use about 10 times as much fruit as knotweed. I've made terrific apple and knotweed pies using this proportion. You can sometimes even substitute knotweed for lemon juice as the tart ingredient in a recipe, to transform the familiar into the exotic.
Nutrition:
Japanese Knotweed is an excellent source of vitamin C.
Medicinal Uses:
If you eat large quantities of Japanese Knotweed, it will act as a gentle laxative, as rhubarb does.
Methods of Reproduction & Dispersal:
Japanese Knotweed spreads primarily by vegetative means with the help of its long, stout rhizomes. It is often transported to new sites as a contaminant in filldirt seeds, sometimes distributed by water and carried to a lesser extent by the wind. Escapees from neglected gardens, and discarded cuttings are common routes of dispersal from urban areas.
Current Manament Approches:
Grubbing is effective for small initial populations or environmentally sensitive areas where herbicides cannot be used. Using a pulaski or similar digging tool, remove the entire plant including all roots and runners. Juvenile plants can be hand pulled depending on soil conditions and root development. Any portions of the root system not removed will potentially resprout. All plant parts (including mature fruit) should be bagged and disposed of in a trash dumpster to prevent re-establishment.
Cut stem treatment:
Use this method in areas where plants are established within or around non-target plants or where vines have grown into the canopy. This treatment remains effective at low temperatures as long as the ground is not frozen. Cut the stem about 2 inches above ground level. Immediately apply a 25% solution of glyphosate (e.g. Roundup, or use Rodeo if applying in or near wetland areas) or triclopyr (e.g. Garlon) and water to the cross-section of the stem. A subsequent foliar application of glyphosate may be required to control new seedlings and resprouts.
Foliar spray method:
Use this method to control large populations. It may be necessary to precede foliar applications with stump treatments to reduce the risk of damaging non-target species. Apply a 2% solution of glyphosate or tricolpyr and water to thoroughly wet all foliage. Do not apply so heavily that herbicide will drip off leaves. The ideal time to spray is after surrounding vegetation has become dormant (Oct - Nov) to avoid affecting non-target species. A 0.5% non-ionic surfactant is recommended in order to penetrate the leaf cuticle, and ambient air temperature should be above 65°F.
Comments from newsgroups and trade sites.
Japanese Knotweed can be easily destroyed by cutting down to 6 inches then blanketing the whole area with 6 ft. overlap of weighted black-out material left in place for three months. Harmless and easy.
Comment:
(It might be best to use a porous permeable membrane like Plantex, ensuring that there is a good overlap and spading in the edges to 12 inches as well as ensuring a thick 3 inch mulch to exclude the light).
SBK: Cut down Japanese Knotweed to approximately 6 inches -beware of sap which can cause a skin rash in some people. Spray stumps with SBK and repeat every six weeks until the job is complete. Residual plant material may still sprout up to two years after spraying has taken effect. Do not dig the ground as this will split roots and encourage growth. Take full precautions when using spray, if only a small area is effected the neat chemical can be brushed onto the cut stems.
'The Times' had a three page article on JK on June 27th. Possible helpful contacts: Sean Hathaway, full time Knotweed Officer for Swansea. John Bailey 'Mr Knotweed' at Leicester University, Biology Department.
Whilst growing spray with glyphosate after crushing the stems to assist uptake.
Comment:
(Best to cut down after flowering, when the plant is weakest).
I've been struggling to kill this plant for the last few years, and only now am I managing to keep it under control (but not kill it). I have bought from a local chemist a hypodermic syringe and I actually inject the plant with neat Round Up. You will need to inject each stem. The leaves will begin to fall off and once that has happened, cut the stems off above where you injected the plant and then pour sodium chloride down the hollow stems. It's quite drastic I know, but this is the first year of success I am having controlling this evil plant.
Comment:
(Be careful!)
When we moved into our house about 15 years ago I was very impressed by this stately looking plant and for the first five years dutifully fed it with all the good fertilizers I felt it deserved. I then discovered it's true identity and since then have kept a long bladed knife by the front door and at every sighting of a new shoot, have leapt forth slashing, Samurai like, with suitable aggressive yells, cutting the growth to the ground. The growth nowadays is definitely weaker and the shoots thinner. (It's also good fun!).
If you find an answer to the control of the Japanese Knotweed, let us know and we will add it to this page - for everyone's benefit.