I am on my third year fighting the dreaded Japanese Knot Weed. It is a vicious thing! I started by excavating FOUR FEET DOWN and an area 12' X 2'. The roots were as thick as my forearm. Then I treated all the new shoots with roundup. Last year I thought I had beat the bad weed. Now I have found 2 more shoots coming up and treated again with round up. It makes me crazy. In England Japanese Knot Weed is known as a "bio hazard because it can take over and destroy all other plants. It has really taken over in the UK but I also get ill about using Round-Up. I do so in as limited fashion as humanly possible because to the best of my knowledge, that is the only thing that will kill the darned weed.

If anyone else knows of a better way, I would LOVE to hear it. They are drenching the UK with Round-Up and the weed is still every where. They can not control it!

I went to this link:
http://www.invadingspecies.com...
Mostly it just said "blah, blah, blah" but at the end there were some downloads available.

The first one is a PDF and it says tarping with a dark colored tarp (or good quality landscape fabric) is the best option which will also not require the use of chemicals. The area needs to be tarped for at least 3 growing seasons to fully 'cook' the roots and the tarp should extend out beyond the area where the Knotweed is currently growing as the plant will be searching for sunlight. This might not be the most attractive look for your property but it is the option that is the least labor-intensive and requires no chemicals.

Edited to add link to the PDF:
http://www.invadingspecies.com...

I will not use round-up by my dog , so I use 1 gallon vinegar - 1 cup epson salt with a good squirt of dish soap. Horticultural vinegar is stronger if you can get it. Is it as good as the brands like round up - not really but it does work on a lot of weeds. Usually brush killers and ivy killers are stronger and might do the job for you.

NJBob said:I will not use round-up by my dog , so I use 1 gallon vinegar - 1 cup epson salt with a good squirt of dish soap. Horticultural vinegar is stronger if you can get it. Is it as good as the brands like round up - not really but it does work on a lot of weeds. Usually brush killers and ivy killers are stronger and might do the job for you.

Sadly, Japanese Knot Weed is a class apart!!! For most of my weed problems I use pickling vinegar. (IE: in the crevices of my walkways and driveway) Most weeds I just spend a few hours pulling after a good rain. For larger weed problems I till and bury, The dish soap would not work well for me because I am situated between a few major waterways and do not want to cause algae problems. (if that formula would work for the dreaded Knot Weed, the UK would have been all over it! ) I am particularly sensitive about using Round Up and very carefully, do just the knot weed using a small paint brush. Using it gives me the creeps so I try hard to not put a drop on the ground. If my problem persists next season, I will do the tarp thing as it does seem to be effective and non-toxic.

The epsom salts sounded interesting! SO, I looked it up: "Completely one-of-a-kind with a chemical structure unlike any other, Epsom salt (or Magnesium Sulfate) is one of the most economic and versatile salt-like substances in the world. Throughout time, Epsom salt has been known as a wonderful garden supplement, helping to create lush grass, full roses, and healthy, vibrant greenery. It has long been considered a planter’s “secret” ingredient to a lovely, lush garden, and is such a simple, affordable way to have a dramatic impact. Just as gourmet salt works with the ingredients in food to enhance and bring a meal to its full potential, Epsom salt enhances fertilizer and soil’s capabilities to bring a deeper level of vitality to your garden’s composition. Ultra Epsom Salt is the highest quality Epsom salt available, and is widely celebrated for its powerful benefits on natural life, ranging from household plants to shrubs, lawns and even trees." Definitely going to use some of that!!

KNOW THE ENEMY! (OR why I would resort to poisons)

http://www.macleans.ca/society...
http://www.dailymail.co.uk/new...
http://www.telegraph.co.uk/fin...
http://www.theweathernetwork.c...

Every person who has ANY bit of this weed MUST eradicate it, ASAP. It really is the terrorist weed and North America still has a chance to win a war against it.

Hi Jennifer,
There was a big aggressive patch of Japanese knotweed at the back of my home. My neighbor and I were both taking measures and tried to avoid chemicals. One year my landscaper tried to smother it with mounds of wood chips - it helped a little, but as you know little bits of it pop up and take off quickly.
This is how our saga ended.
At the end of the season a few years ago I tossed out into the back of my yard a few Long Island Cheese pumpkins - just heaved them out there where they disintegrated. We had gotten too many from our CSA. The next year in the fall we saw a huge pumpkin vine. Somehow it created a hostile environment for the Japanese knotweed. The only "downside" is that the pumpkin vine went everywhere and volunteers each year, but I would so much rather deal with an "invasive" pumpkin vine than the dreaded knotweed.
Good Luck!

Use tordon for the knotweed. It's a heavy duty brush killer and will work better than RU. We had an outbreak of invasive bush honeysuckle here (our fault but we learned from it) and the only thing that worked was tordon. It can't be found at Home Depot or Lowes but can be found at farm and home stores like Feldmans.