Japanese Knotweed Myths & What Does Work?

Japanese knotweed is without doubt one of the most infamous invasive vegetation in temperate gardens—nevertheless it’s additionally some of the misunderstood. Let’s bust some myths and clarify the most recent science on the right way to management it.

Key Takeaways

• DIY options don’t work.
• Commonplace options used for different weeds additionally don’t work.
• Herbicide spray works finest, nevertheless it nonetheless takes a few years and needs to be completed accurately.

Get to Know Japanese Knotweed

Japanese knotweed (Reynoutria japonica, synonyms Fallopia japonica and Polygonum cuspidatum) is native to jap Asia and was launched to North America and Europe as a horticultural plant within the late nineteenth century. It grows in a variety of habitats, forming dense thickets of bamboo-like vegetation that aggressively outcompetes vegetation which might be shorter than itself.

Stems are hole as much as 2.5 cm in diameter and kind horizontal rhizomes that unfold shortly as a lot as 10 m away from the mum or dad plant. 

12 Myths About Japanese Knotweed

Delusion #1: Knotweed Pierces Concrete Foundations

This can be a widespread perception that has no foundation and has been debunked by research within the UK. Roots and rhizomes will develop into cracks within the basis and, over time, will widen them, however this doesn’t trigger the unique harm.

The roots additionally don’t develop into and harm water pipes.

Delusion #2: Roots Develop 16 Toes Deep

Roots can develop as much as 5 toes deep in sandy soil and are even shallower in heavy clay soil. The actual drawback is the rhizomes, which may journey a good distance from the mom plant.

Delusion #3: Excavation is Efficient Management

Though the roots should not very deep, excavation will not be an excellent management methodology as a result of roots and rhizomes simply break off and begin rising once more.

Delusion #4: Rhizomes Stay Viable for 20 Years

Rhizomes retailer vitamins and survive for years, however there’s no scientific assist for 20-year dormancy. Most viable items die off in below a decade.

Delusion #5: Knotweed Spreads by Seed

In North America and Europe, virtually all knotweed colonies are clones from rhizome fragments, not seeds. In 1842, Phillipe von Siebold, a health care provider who labored on the Dutch buying and selling settlement in Japan, returned from his expedition to Europe and introduced with him the primary dwell samples of Japanese knotweed. It was cultivated and unfold from there.

It was believed that each one of those vegetation have been feminine and, subsequently, no seeds have been produced. Nonetheless, a male specimen of Japanese Knotweed was present in Southern England in 2021, and analysis is underway to learn the way this male plant arrived. Launched male vegetation might imply that the plant begins spreading by seed.

Delusion #6 Japanese Knotweed is Toxic

Japanese knotweed is not toxic and has been used medicinally and in meals and drinks for many years. It is usually innocent when touched and is secure close to pets.

Delusion #7: Knotweed is Allelopathic

Though lab assessments have discovered poisonous compounds within the plant, they aren’t concentrated sufficient to suppress different vegetation. They prohibit different vegetation from rising by being aggressive and shading them out.

Delusion #8: You Can Kill It With Diesel, Bleach, or Glyphosate

It’s claimed that you may minimize it down and pour varied concoctions into the hole stem to kill it. Frequent gadgets embrace diesel gas, bleach, and salt. These don’t work. Even glyphosate (Roundup) has a restricted impact.

Delusion #9: Mowing Eradicates It

In concept, this could work. Repeated mowing will finally exhaust the underground tissue, however this methodology can take a few years. It’s not an efficient management methodology.

Delusion #10: Herbicides Will Work

Systemic herbicides like glyphosate can management the plant, however they hardly ever remove it until repeated for a number of years. Organic herbicides and make contact with herbicides, like vinegar, don’t work.

Delusion #11: Tarps Starve It Out

Lengthy-term geomembrane overlaying is usually ineffective. Even six-year tarping could not cease the plant, as hardy rhizomes discover cracks and persist.

Delusion #12: Thermo-Electrical Therapy Works

Thermo-electric remedy entails making use of as much as 5000 volts on to the knotweed, boiling it from the within out, and depleting its vitality reserves, making it very laborious to regrow, or at the least that’s the declare.

Such companies are actually obtainable within the UK, however I discovered no proof that they’re efficient. One website claims that “thermo-electric remedy will not be a one-off, however sometimes requires a number of visits throughout a 5 to 10 yr plan”.

Greatest Solution to Eradicate Japanese Knotweed

What does science say? What’s the easiest way to do away with this weed?

The simplest remedy is to apply herbicide to the rising plant. Spray early within the season as soon as leaves are absolutely prolonged. This ensures most absorption of the herbicide. Then spray once more later within the season. This should be repeated over a number of rising seasons.

Some USA extension workplaces advocate a single fall software after slicing the plant again in mid-summer.

The place spraying will not be an possibility, stems could be in the reduction of and herbicide utilized into the inside of the stem, or be painted on the outside of longer stems. However these strategies are a lot much less efficient.

“Glyphosate is the herbicide of selection for controlling knotweed. It’s efficient, has no soil exercise, is available, and considerably cheap.” The blended resolution ought to have 5-8% glyphosate.