no one can identify this spreading weed

20 years ago

There are these reddish purple shoots coming up around my house, and at the edge of my yard. They kind of look like asparagus. They are in various stages of development, some are now about a foot tall and sending up more shoots, appears to be spreading. The stem is fleshy, not as much as a succulent, the leaves are more delicate, not hairy, alternate, rounded, and about 4 inches in diameter. They are a dark green veined with reddish purple, and slightly curled under. Upon digging the root system is extensive, growing laterally, and spreading at all levels of ground, down to 4 feet. The largest roots were almost 2 inches thick. The stalks left in winter are about 5 feet high, and are hollow and reed like ( this is not a reed though) This is my first year living here, so I do not know if it produces flowers yet. The soil is very sandy here. It appears very resilient, and is starting to come up through the cement. any ideas? help!

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Comments (4)

morz8 - Washington Coast
20 years ago
Japanese Knotweed? Description: New shoots asparagus-like and green to purple/red, fiberous roots, hollow stems.

Here is a link that might be useful: {{gwi:1341722}}
tenuviel
Original Author
20 years ago
this is defidently it. Thank you. Any earth friendly way of controlling it?
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morz8 - Washington Coast
20 years ago
Happily, I haven't had to deal with knotweed personally...

but it doesn't sound good - this is one tough and invasive plant. Hopefully someone else (or your county extension agent) will have some suggestions for efficient long term removal, but it looks to me like you will be at this for a while and will need to use more than one method of control. Wish I had better news...

Mechanical

Large colonies of this species are extremely difficult to dig up due to their high rhizome densities. Digging of large colonies is not recommended as it is very labor intensive and unlikely that all below ground material can be removed. Small patches may be dug, however care should be used in removing plant material as improper disposal can spread the species further. Repetitive cutting or mowing within a single growing season to deplete stored reserves and remove photosynthetic tissue has been effective. Eradication of the rhizome system is necessary for control of this aggressive invasive species.

Chemical

Herbicide has been generally effective at controlling this species. Repetitive cutting of stems with spot application of RoundupÂ®, AccordÂ® or GlyproÂ® to the stumps, and foliar spraying in large populations has been reported to be successful.

Biological

There are currently no biological controls available for Japanese knotweed.
kalmia10
20 years ago
Glyphosate is effective at about a 3-5% rate in a foliar treatment. Don't waste your time spraying at this time of year though. We have found it works well to bend or cut the stems in June/July and come back in late summer/early fall and treat the shorter regrowth: not as much product used, less exposure and drift since the plants are shorter, and the translocation of the herbicide to the roots is best in fall. Not sure if this is suitable for your situation but it does work well. Good luck!