SitNews - Stories in the News - Ketchikan, Alaska


Japanese Knotweed Removal
By Samantha Quinn


July 28, 2010

I was reading the letters regarding the Japanese knotweed problem some are having and found this information on on it's removal. I hope this helps!

Taken directly from

"Japanese knotweed has a large underground network of roots (rhizomes). To eradicate the plant the roots need to be killed. Picking the right herbicide is essential, as it must travel through the plant and into the root system below. Glyphosate is the best active ingredient in herbicide for use on Japanese knotweed as it is systemic ; it penetrates through the whole plant and travels to the roots. Glyphosate is available under several trade names - all label the product as a "weed and grass killer". Commercial glyphosate concentrates contain approximately 20%-40% glyphosate; the balance is mostly water. Such concentrates need to be diluted in water.

The most effective spraying solution contains about 5%-10% glyphosate in water. (To make a 5% solution from a 40% concentrate mix 1 part concentrate with 7 parts water.) Ready-to-use solutions that contain less than 5% glyphosate are too weak and do not work. A small amount of liquid dish-washing detergent can be added to improve wetting of the leaves. If possible, both sides of the leaves should be sprayed until they are completely wet. It takes about 3 weeks for most of the plants to die. After 3 weeks, all remaining plants should be sprayed again. This process needs to be repeated until all the plants die.

The US federal government will come and spray Japanese knotweed for no charge in many areas under the Invasive Species Act. Local county extension agencies can be contacted for more details.

More ecologically friendly means are being tested as an alternative to chemical treatments. Soil steaming involves injecting steam into contaminated soil in order to kill subterranean plant parts. Research has also been carried out on 'Mycosphaerella leafspot fungus, which devastates knotweed in its native Japan. Research with Mycosphaerella, has been relatively slow, due to its complex life cycle.

In the UK, where over £150M is spent annually on Japanese knotweed control, a decision was taken on 9 March 2010 to release a psyllid insect, Aphalara itadori. Its diet is highly specific to Japanese knotweed and shows good potential for its control."

Samantha Quinn
Ketchikan, AK


Editor's Note:

"Weeders" are the absolute best in controlling & eliminating weeds. Brown China Geese are non-toxic and are big, lovable pets. Mint farmers have used these amazing creatures for years as weeders. They would require care -- more work than toxic chemicals but more rewarding.


Received July 27, 2010 - Published July 28, 2010


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letterConcerned about Japanese Knotweed By Melinda Stewart

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