Mugwort (Artemisia vulgaris).

It responds well to Roundup sprayed in late summer/ early fall. It may take several sprays to get it all.

It spreads by rhizomes and while new infestations can be controlled by hand-pulling, doing so in impacted soil is impossible.

Ooops. Should have said "compacted soil".

Not sure what impacted soil is, but I'm pretty sure I wouldn't want it. :)

I have successfully dealt with a large mugwort infestation. Don't give up hope.

Wow--I think this might be the herb that my Japanese mom values so highly for almost every kind of ailment. She keeps bringing and planting things at my house. I understand why she does it, but am not very appreciative of the way that this one is taking over the garden intended for my butterflies.

Mugwort, "Artemisia vulgaris", is an herbal, medicinal, sometimes desireable, often is considered a "weed". You couild spend a lot of money spraying a plant poison to try and control it, dig it out if it is not a desirable plant, or live with it.
Any of the plant poisons are not environmentally friendly and some research indicates they will make changes to our genes over time.

I agree that weedkillers are not the best thing ever, but Artemisia Vulgaris will continue to spread aggressively and will soon take over everything if not controlled. It forms a monoculture because its dense roots block out everything else. You can try hand-pulling if the area is small. Start from the sides when the ground is soft and work towards the middle. Try to get as much root as possible (it will grow a whole new plant from a tiny piece of root; that's what rhizomes do). You will need to repeatedly pull new growth, trying very hard to get the rest of the root when you do so. I've had success with hand-pulling in loose soil (think years, not days), no success with hand-pulling in compacted soil.

It will happily live forever at mowing heights as far as I can tell, so your control options are limited to hand-pulling or weedkiller. It will grow up through cardboard and other natural mechanical barriers.

Since my own mother WANTS it to grow (and I want it contained), I intend to ring it with a sheet of galvanized metal, buried about a foot deep and with a couple inches protruding above the ground to prevent spillover. I'll have to put something over the sheet metal where it comes out to prevent anyone from getting cut on it.

The things we do for our mothers...

Although I'm a frequent lurker of the forums here, I wanted to send out a huge THANK YOU to anyone who contributed to this topic, especially to Soitgoes!!! I spent a few hours yesterday trying to identify this nightmare of a weed and decided to stop my google searches and head to Gardenweb.

Deborah- I feel your pain, 3/4 of my back yard has been taken over by this and I am overwhelmed at the amount of work it will take to remove it (sending out a huge sarcastic "thanks" to the previous homeowners, who were probably very relieved to show their home in November and close in February before this problem was revealed.)

Trying to remove it, or at least curb it's growth, will be the project of my summer and autumn.

And Ralleia, please consider growing this in some type of container and not allowing it to go to seed. If you lived in NY I could give your mom a dump-truck full!

I have another weed that I have named the weed from hell. It is Poa Annua. My thick bermuda lawn is now ruined because I did not know what it was. It is almost impossible to kill. It reseeds itself and returns thicker and more prolific than ever, it n;ow covers 90% of my yard. Any ideas of a cure for it?

From reading this article on it (http://www.hort.iastate.edu/directory/people-files/nchris/RRBGrounds.pdf), it sounds like a formidable adversary. I don't envy you the fight.

If it is an annual, then I would attack it by preventing its seeds from germinating. The article mentions Rimsulfuron (TranXit GTA) as a promising pre-emergent. I don't know if it is commercially available or requires special licensing...

I was planning on starting to use corn gluten as a natural pre-emergent against the reseeding weeds in my own lawn of perennial fescue and perennial bluegrass--I tried to find out if it might be effective against the annual bluegrass, but apparently no one has done and published that research yet.

"Poa Annua", annual bluegrass, is sold as a nurse grass in many lawn seed mixes because it can germinate fairly fast and cover quickly. Generally this is a fall germinating seed so a pre emergent, Corn Gluten Meal, spread in early September may be the best control.

Just as a follow-up to my Mugwort research, it appears there was a study done that showed the herbicide, Picloram (sold as Tordon or Grazon,) was VERY efficient at treating Mugwort.

Unfortunately, Picloram cannot be sold, shipped or applied in the NY county where I live, so that isn't an option for me. Perhaps it would be an option for areas where the water table isn't as high and there is no risk of drain-off into waterways or wells.

Here is a link that might be useful: mugwort control research