Japanese Knotweed

We have some in our yard that we have intended to pull it out once we figure out the best strategy. I have heard conflicting views on how to get rid of it. Apparently, digging the roots is not as effective. I've read that, much like U2:the univited guest to my iPod party, it will pop up again and spread if not correctly removed. Anyone with a sure fire way to irradicate it?

Even though it is an unpopular choice with many people, it appears that repeated applications of glyphosate (roundup) is the recommended strategy. It is also recommended that shoots and roots are double bagged and disposed of at the dump. 

Even though it is an unpopular choice with many people, it appears that repeated applications of glyphosate (roundup) is the recommended strategy. It is also recommended that shoots and roots are double bagged and disposed of at the dump. 

To kill japanese knotweed as well as other plants like poison oak, ivy, etc. that can come back stronger if roots are severed and bits left in the ground, I have used roundup in a needle and injecting the solution as far down into the root mass as you can.  This is a long and tedious process but it does work after a few repeat applications.  As roundup inhibits the plant's ability to photosynthisize you can also use a combination of the herbicide, dish detergent and water and paint it on the leaves (see greg the gardener on youtube for a demo). Painting with a brush rather than spraying is a more precise application. This takes more applications than injection but over time does kill the plant.  

Make sure you wear protective gear as any contact with the herbicide can make you feel quite ill. Also, if painting it on the leaves run a tape barrier around the plants so kids and dogs don't brush up against it. 

You can call me if you want to talk it over.  Gillian 250-231-6529

http://ckiss.ca/species/invasive-knotweeds/

CKISS central kootenay invasive plant society has a whole webpage on invasive plants and animals. There's lots of good ideas for control and if you contact them they might come do it for you as part of their program. 

Probably everyone knows this but ... if you use roundup or any herbicide, don't grow anything edible on that ground for many many years.  Any plant may have a hard time thriving on that ground for a few years. Regardless of Monsanto's claim that roundup's half-life in soil is months, it has actually been found in lettuce and other edibles grown in soil treated with roundup over 3 years previous (you can search Mother Earth News, Rodale's Organic Gardening or COG - Canadian Organic Growers for published results) 

Gill

If you are really interested in this, as I was last year, there was also an episode on CBC's The Current about it:

http://www.cbc.ca/radio/thecurrent/the-current-for-june-19-2015-1.3119751/destructive-japanese-knotweed-sprouting-in-canada-brace-yourself-1.3119781

And if all this has you staying up at night worrying that knotweed is going to take over the world, there is a different perspective. Perhaps invasive species could save the world:

http://www.cbc.ca/radio/thecurrent/the-current-for-october-21-2015-1.3281453/war-on-invasive-species-wrongheaded-says-author-fred-pearce-1.3281529

I still don't want it anywhere near my house tho! 

It appears some folks in Rossland are looking for guidance on how to control knotweed and prevent further spread of this invasive plant. Unfortunately there is no silver bullet to eradicate this plant; however, the Central Kootenay Invasive Species Society (CKISS) can provide you with the most recent best management practices kntoweed control.

Invasive Species Primer

Invasive species are considered to be the second biggest threat to biodiversity after habitat loss.

The homogenization of biodiversity through the intentional and unintentional introduction of invasive species is accelerating. Increased global trade, transport and tourism, has expanded the movements of organisms from one part of the world to another through newly created pathways.

Many species introduced into new environments are unable to survive in their new surroundings. However, a percentage of these species are able to expand the area they infest and negatively impact the economy, human health or ecology of a region and are termed invasive. Habitat alteration and invasive species impacts have been the major cause of species extinctions over the past few hundred years, increasing the rate of extinction by about 1,000 percent.

Knotweed is no exception. Dense thickets of knotweed can reduce sunlight penetration by more than 90%, preventing native plants from growing. Studies completed by Cornell University have found that knotweed negatively affects the diversity of vegetation, reducing native species ground cover within knotweed stands to 0%. That is not a typo, 0%! As a result, knotweed stands do not support native amphibians, reptiles, bird and mammal populations as native vegetation does.

So how do you get rid of it?

Mechanical Control:

Knotweed spreads and reproduces vegetatively from rhizomes and roots and may reproduce by seed (studies currently in progress). Knotweed can spread rapidly due to its ability to spread vegetatively from the roots or from any of the nodes along the stalk. Each node on the plant stalk is able to produce roots and new plants.

Cutting may be used to control very small patches of knotweed (no more than 30 stalks). Control must be completed TWICE A MONTH OR MORE, from April to October. Treatments will take anywhere from 3-5 years and upwards to 15 years. DO NOT MOW any part of the infestation; even a small plant fragment can cause a new infestation. Machinery and equipment may transport and spread plant material causing new infestations.

Digging and excavation is not recommended as root fragments as small as 1 cm can form new plant colonies and the roots can extend very deep up to 2 meters and out from the last above ground stalks up to 7 meters. As such excavation and digging are not recommended treatments.

Unfortunately no studies to date show that covering or smothering are an effective long-term treatment.

To dispose of the cut knotweed it is best to lay the plant material out to dry (until brown) and then all plants parts should be double bagged and brought to the landfill, you must tell the site operator that you have invasive knotweed, prior to disposal. Do not compost any plant parts.

Please do not illegally dump plant material. CKISS annually finds new infestations of knotweed along forest service roads and highways due to illegal dumping of garden waste.  Please note there are significant fines associated with this activity. In 2015 we found a large pile of knotweed that someone illegally disposed on the wagon road at the bottom of the Whiskey trail, it took us hours to load it into the truck and dispose of it properly and now we need to monitor that site for 5 years to ensure no knotweed becomes established. This may seem harmless but knotweed has significant environmental and economic impacts and has significant costs associated with its treatment.  Disposal of invasive plants is free at the local landfill.

Herbicides:

Unfortunately this is one tough plant to eradicate. To date, the only effective known long-term method of treatment for knotweed includes the use of herbicide application.

Please follow this link for information on appropriate herbicides to use to treat knotweed. http://bcinvasives.ca/documents/Knotweeds_TIPS_Final_08_06_2014.pdf

It is highly recommended that you seek a qualified herbicide contractor to complete these treatments. This will save you time and money in the long run and will ensure eradication of the infestation.

It is imperative that the label is followed for any herbicide utilized to control invasive knotweed; not following label rates will drastically reduce the effectiveness of any herbicide treatment. NOTE: stem injection is not currently on the label of any of the preferred herbicides for knotweed control.

The Central Kootenay Invasive Species Society (CKISS) is a non-profit society that delivers education and awareness programs, and promotes coordinated management efforts of invasive species within the Regional District of Central Kootenay and teh Regional District of Kootenay Boundary Area A and B.  CKISS acknowledges the support of its many funders, including the Columbia Basin Trust.