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I'm located in northern Utah, USA.

There is a weed which is proving difficult to control, which I haven't been able to identify.

Tall Ground Runner Weed

It is usually fairly easy to pull, but you only get a small bit of root because these things spread via an underground runner. Usually there will be dozens all along one run, yet removing them all is almost impossible because of surrounding plants that I want to keep.

The one pictured is in the seeding stage, I usually try not to let them get this far.

What is it, and is there some type of control that is especially effective on it?

Edit:

I am adding two additional photos as well as links to larger resolution versions.

Base of weed.

(Click for high-res of base)

Top of weed.

(Click for high-res of top)

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It doesn't really look like it from the picture, but I suppose it might be a knapweed of some sort (Centaurea sp.). Could you post close-up pictures of the flowers (it would help if you could get a shot of the phyllaries -- the little scale-like leaves at the base of the flowering head), as well as leaves on the stem, and a picture at the base of the plant to see if there is a rosette of leaves there. –  Steve K Sep 4 '11 at 1:16
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3 Answers 3

up vote 11 down vote accepted

It looks like a type of fleabane. I'd say hairy fleabane, yet it is an annual and you mention it spreading by rhizomes. I suggest you check with Utah Pests http://utahpests.usu.edu/uppdl/. For only $7, they can ID it for you and tell you how to control it. Deal!

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Thank you for posting your "expert" answer & please pass on my thanks to Stephanie Porter for asking you to look into this question. Your expertise & time is greatly appreciated by myself... –  Mike Perry Sep 7 '11 at 15:37
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I'm going to stick with my initial thought (as soon as I saw the photo):

Though without seeing all of the weed (at ground level) I'm not 100% on the above. Another possibility:

* Hoary Cress (Direct link to PDF) from Utah State University Cooperative Extension

Both the above PDF's contain Control information.

Listed below is further weed related information, resources from Utah State University Cooperative Extension:

The 288 page, free PDF "Weed Management Handbook" from Montana, Utah & Wyoming Cooperative Extension Services is available from:


Missouri University Extension Office recommended I try this service:

So I did, here is the result:

Your Question

Could you please identify this plant (additional images viewable via URL): What is this weed and how do I get rid of it?

My location is... but the plant is located in Northern Utah.

Responses

I am wondering if it could be a knapweed; possibly diffuse knapweed (Centaurea diffusa). See http://forestry.usu.edu/files/uploads/NR_FF/NRFF012.pdf. However, I am a tree expert and non-woody weeds are a little beyond my expertise. Knapweeds are common out here in Utah.

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@JYelton, thanks! I've removed my "Hoary Cress" guess (it's most definitely not that). "Common Yarrow" is looking less unlikely now, seeing as the flowers look like they will have a "yellow" centre, surrounded by "white" petals: redtailed.com/se/weed_top.jpg –  Mike Perry Sep 6 '11 at 21:00
    
@JYelton, are the stems &/or leaves hairy? From the photos I would say they aren't, but could you please confirm. Does the plant have any kind of smell (from the flower itself, or maybe if you crush a leaf)? If you snap a stem does a white "milky" substance come out? –  Mike Perry Sep 6 '11 at 21:04
    
I'm not at all familiar with the flora of that area, but based on the flowers, maybe an Erigeron (fleabane)? –  Steve K Sep 7 '11 at 0:18
    
@SteveK Could well be: Daisy Fleabane -- with its smoother stems & leaves... –  Mike Perry Sep 7 '11 at 0:20
    
Erigeron looks good - an open flower would sure help. One thing that bothers me about both Erigeron and S. Bicolor is the O.P.'s description of the root habit - it doesn't sound like either Solidago or Erigeron, does it? –  Ed Staub Sep 7 '11 at 12:47
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I'm going to go out on a limb and guess that it's Silver-Rod (Solidago Bicolor) - even though I don't think it's supposed to grow that far west. We have a lot around here in New Hampshire.

It's definitely not yarrow - the foliage is all wrong. The leaves look wrong for hoary cress, too - too small and narrow - though I'm less confident on that.

It should go to seed soon - maybe that will help identify it.

Update Sept 5 '11

The new picture of the top shows white petals and yellow stamens, consistent with s. bicolor. Seeing an open flower would be helpful - the pictures are either buds or flowers gone by.

Google images for solidago bicolor, and also see this guide. Plants get around, and guides get out of date - it wouldn't be at all surprising if it hitchhiked into the state one way or another. You might want to have a chat with your county agricultural extension office, but they vary a lot from state to state.

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It's definitely not hoary cress -- wrong family. It's in the Asteraceae. –  Steve K Sep 4 '11 at 1:02
    
It has both disk and ray flowers, so it's not Solidago. –  Steve K Sep 7 '11 at 0:12
    
@Steve, I'm no botanist, but the guide I referenced above mentioned that for Bicolor, Both ray and disc florets are WHITE. Doesn't that imply that it has both? –  Ed Staub Sep 7 '11 at 12:24
    
Doh. Yes. And I am a botanist, or at least I was one 10 years ago. Can I use the "I was drinking and skyping while stackexchangeing" excuse? –  Steve K Sep 9 '11 at 15:09
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