canadian thistle

harrylauderJuly 11, 2002

I seem to have a nice stand of Canadian Thistle in my

2nd year wildflower garden.

Any ideas on getting rid of them?

To make matters worse, I noticed the stems I did get around to pulling just shot up more flower heads.

I'm thinking about taking the weed trimmer to them?

thanks in advance for any help

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froggy(z4/5 WI)

canada thistle can be one of the most frustrating weeds out there. it grows in groups of underground root system called a colony, its growth habbit is colonial. so to kill just one or two or some or most isnt enough.
my advice is this;

weed wack it so that nothing flowers all year long. then spray it with a 'trimec' or 'triplit' solution in the early fall of the year( u can also use round-up). in wisconsin i usually spray around sept 1st - 15th.
do this for 3 years and u can get control of it. i know i know...3 years??? if someone has another way id sure like to know about it.


    Bookmark   July 11, 2002 at 7:02PM
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Rosa(4ish CO Rockie)

Physiologically, canada thistle has lots of adventious root buds. It's what makes it so hard to kill. Cutting at the ground level stimulates additional root bud development. However, cutting high at 8-10 inches retains the chemicals in the stem (auxins) and fools the plant into thinking it is still producing flowers, and root bud developemnt is retarded. Also, studies show that plants of that height are more suseptible to chemical damage and will translocate better to the roots. Do not let the flowers open. Even if they have been opened for a mere day or two, and the flowers are cut (and thrown on the ground) the seed will still ripen and be completely viable.

Spring treatment yields greater top kill and poorer root damage, fall treatment yields greater root damage but it is harder to penetrate the leaf tissue and visually the top kill is not as spectacular. Adding a surfactant will aid greatly in sticking to leaf surfaces and allowing penetration to the roots at any time. Do not spray during drought it you can help it. The waxy cuticle on leaves thicken with drought and prevents absorbtion. Also, pores (stoma) on the leaf are closed during drought.

No one method works by itself. There is no silver bullet. Maintaining good ground cover in terms of light, nutrient and water competition will also go a long way to discouraging canada thistle when combined with other mechanical or chemical measures.
Trimec is 2 4-D.

    Bookmark   July 12, 2002 at 7:35AM
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froggy(z4/5 WI)

i agree with everything that Rosa said, that is why i gave the prescription that i did. also by weed wacking, u stunt the growth and not really stimulate it much. it really does work after a few years.

one added comment; "Trimec is 2 4-D." trimec is a 3 chemical mix (hence the name Tri.) that is made up of 2,4-D and dicamba and mecoprop. This chemical mix is for broad leaf plants only and is very effective. if 24D doesnt get it, the others will. I actually use something by the name of "triplet". its the same thing but cheaper but i dont know if u can get it all over the USA.


    Bookmark   July 13, 2002 at 8:10AM
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When I was a kid we lived on a 40 acre farm in southeastern Ohio. Every summer my dad would pay me .05 cents bounty for each Canadian thistle body I cut. I cut them off level with the ground and poured about a teaspoon of table salt on the stump. It killed them outright. When I visited that same farm several years ago I still didn't see any thistles 30 years later!


    Bookmark   July 14, 2002 at 8:07PM
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Thanks again for the tips
Benji you are hired!

    Bookmark   July 15, 2002 at 9:48AM
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froggy(z4/5 WI)

yea benji...when can u start and do u still have a good salt shaker?

    Bookmark   July 16, 2002 at 11:42AM
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Use full strength vinegar as a herbicide. According to the research on use of vinegar as a herbicide, Canadian Thistle can be killed by spraying it full strength with vinegar. It is one of the plants that was easily killed with a 5% vinegar - the kind you buy a grocery store for making vinegarette. You can also use a 10% - the kind that is used for pickling, but the extra strength is not necessary for the thistle. Best time to spray is on a sunny, preferrably hot day. You may need to spray again if the plant comes up from the roots, but after several successive sprayings, I think you will succeed. And for those of you who may be concerned about changing the PH of your soil - the researchers found that vinegar will change the ph only for a couple of days. It will go back to normal after that.

Salt is an effective way to kill plants of most any kind, but it has a very long term negative affect on the soil. If you spread salt over an area to kill a weed, you will not be able to get anything to grow in that area for years, maybe decades. I strongly discourage the use of salt.

Here is a link that might be useful: Vinegar as Herbicide

    Bookmark   July 29, 2002 at 12:17PM
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Rosa(4ish CO Rockie)

Sorry, but canada thistle will not be killed with vinegar in any solution. It is not translocated into the roots where new plants are formed. You may see the death of the tops, but you won't kill the root this way.

    Bookmark   July 30, 2002 at 9:07AM
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flapper(z4 MN)

The state Dept. of Nat. Resources officer who took a look at my restoration site said I should walk the field and spot spray isolated thistles with Roundup. I don't have a lot of Canadian Thistles, and he said I should wipe them out if I keep after them for 2 years. Anyone else used Roundup on thistles? I think I'll try mixing up a solution on the strong side and try the sponge method to avoid drift. You buy a throwaway painting sponge (like a small paintbrush, but with a sponge on the end instead of bristles) and touch the saturated sponge to the plants you want to get rid of.

    Bookmark   August 3, 2002 at 12:45PM
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Roundup works well. We moved into a new house last August and the yard was covered in thistle. I sprayed every new shoot in the front flower beds with roundup. So far this spring I have only had 2 come back. Now the side yard is giving me more problems. You just have to keep at it and eventually it will go away. Also roundup works better the hotter it is. When sprayed in 80 degree weather the plants will be black withing a couple hours. Good luck to all.

    Bookmark   May 2, 2003 at 10:49AM
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Rosa(4ish CO Rockie)

Yes, Roundup will eventually work. It has to be repeated over the summer for several years. Do not spray in really hot weather-over 90 degrees. Roundup is supposed to take some time (ususally 5-7ish) to be translocated thru the plant. More is not better, hotter is not always better and don't be fooled by thinking that if the plant does not show signs of immediate death the product is not working. Read and understand the label before using any herbicide!!

    Bookmark   May 3, 2003 at 9:25AM
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I saw over on a posting about dandelions that several people use a "Weed Hound". Has anyone tried that with canadian thistle??

    Bookmark   May 20, 2003 at 10:04AM
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We had a small patch on the old place and heres what an old farmer that lived near us told us to do and it seemed to work. Always make sure you chop them off before they bud, leaving some of the stem. Then hit them at the crown with a blow torch. You burn away at the crown for 30 sec or so on a full grown plant and then go around and get the babies. DH the pyro loved this, what fun. You have to be on the look out for it restarting from the roots for the next 3-5 years and ever after for seedlings and these things can live in the soil for ever and then sprout one day. Even the folks using chemicals have to be aware of the seed bank.

    Bookmark   May 21, 2003 at 12:36PM
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mtcrafter(z4/5, MT)

We have had severe infestations of Canadian Thistle several years ago. After the introduction of Roundup, we've eliminated all but the seedlings that come up here and there. We spray them 2 or 3 times according to directions and get a good kill. We've also done in large colonies in the grain fields after the harvest. We irrigated to bring up strong new growth and then sprayed them. When the thistles are in amongst your flower beds, mix up the Roundup in a small bucket and using a paint brush or even better your hand with a rubber glove on it, dip it in the mix and paint or grasp the weed to get it wet. That way it doesn't get on the plants you don't want killed. We've used it in our lawns to spot kill tough orchard grass spots. Then we have to reseed later to get the grass back.

Like all chemicals, read the directions and follow them. Don't think that more will be better. It won't!

    Bookmark   May 24, 2003 at 12:06AM
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I didn't read all of the posts and so I hope I'm not redundant.
Is there anything redeeming about this invasive weed? Can it be made into a fertilizer tea? What nutritional value, if any, would it have if it were made into a tea? And what kind of application?

I have a couple of fields of CT and wondered if I could use them to my benefit.

Thank you...

    Bookmark   July 3, 2003 at 3:41PM
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Gold Finches love them.
My wife has us in trouble with the neighbors because her two acer bird sanctuary is being run over with Canadian Thistles. She wont have any part of using Round up. With all the farmers using round up ready crops, I have to agree with her that enough is enough. We don't care about the Thistles but the neighbors do have a point...or do they? They don't really have a problem keeping the Canadian Thistles down in there fields any more since they spray roundup ditch to ditch.
I don't really have a question I guess except maybe what do you all think of some one who wants to let the Canadian Thistles grow for the wild life?
We have also seen a fox some quail and so many variates of birds I wouldn't no where to start.
I'm a third generation Indiana farm boy and I was brought up not to let weeds live. LOL But with the fence rows a think of the past ( the over spray of round up kills every thing in whats left of the ditches... less than three feet often times around here.)somebody's got to give the critters some place to go.
Hi every one I just found this place and I'll be back.

    Bookmark   August 31, 2003 at 12:01AM
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Rosa(4ish CO Rockie)

Welcome to the forum leadarrows.

PLEASE don't do it!! There are plenty of other NATIVE plants and native thistles that can be planted for wildlife.
Seriously, this is a bugger of a plant to get rid of. And your neighbors are justified (whether they be farmers or not, in wanting you to get rid of this). I'de personally be plenty pissed off if I spent all that time and money trying to keep this weed controlled only to have the neighbor's land overrun with the stuff. It WILL spread back onto their property.

Roundup is virtually nontoxic to wildlife and it also breaks down very fast. You can get the label and MSDS sheet online-I suggest you read both. The MSDS sheet will give you more info on avian and mammal toxcitity and the half life of this chemical in the soil.

Just remember that Roundup is a non-selective herbicide. It will kill everything it's sprayed on (that's green) so plan on starting over when you are done or going with a selective broadleaf herbicide to leave the grasses (and then replanting with the appropriate broadleaf plants for your avian friends). And, any treatment on this weed is going to take more than one growing season-especially with the kind of infestation you have.

    Bookmark   August 31, 2003 at 10:03AM
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I know about round up I got my first herbicide licenses in 1985. We spray tons of the stuff on our beans. I don't like it. The over spray kills every thing. The trees and all. Where are the critters suppose to live? My neighbors use round up as well and There is no thistles in any of the fields adjacent to mine. With the introduction of round up ready crops the old views of weed spreading to neighbors fields is out dated. Gold Finches like thistle seed and sun flowerer's. We are looking more at tillage control of this particular field. Strip tillage would reduce the number of thistle plants while leaving enough for the wild life. We hope to gradually introduce other native wild flowerer's and natural cover. I'm looking for more suggestions along those lines. I'm a fourth generation Indiana farm boy but I do have some untraditional ideas.
And I'm looking to learn some more.

    Bookmark   September 17, 2003 at 5:19PM
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thatbiologygirl(NW IN)


If you have CT, you can't plant anything around it. It will over run everything, period.

It isn't the CT spreading to your neighbors I worry about. It can spread farther than that by migrating song birds and be dropped of in the middle of a descent prairie. If you can, you really should get rid of it. Seriously, it really does spread far because of the birds. When I worked on the Kankakee Sands Prairie restoration project we had a CT problem that came from no where. The nearest thistle stand that I noticed was miles and miles away.

You don't even necessarily HAVE to use roundup, there have been lots of non-round up CT killing suggestions posted here.

But the bad thing about it is, the worst threat to natural areas in Indiana isn't chemicals or habitat loss... its invasives. I've seen so many awesome areas wiped out in less than five years because of garlic mustard, honeysuckle, rosa multiflora and CT. And the biggest problem is that people aren't AWARE that invasives are a problem. They hike in a garlic mustard infested woods and don't clean there boots off before going somewhere else. The seeds get tracked in and its curtains for the natives. Sorry to rant a bit about this, but like I said, it's a big problem. And big though it may be, it isn't really anyone's fault because it is a problem of ignorance. People go into a wood and think that because it is green it is natural and healthy. They don't know that a green wood can still be a biological wasteland.

In addition to this, invasive plants lead to loss of habitat as much as development because they can create monocultures. A primary principle of ecology is that of resource partitioning. The more different types of resources (food items for example), the more species can coexist. You can get an idea of this by comparing the number of species of beetles in a rain forest and in a lawn. Well, the lawn has at best ten different prey species. But the rainforest has thousands of possible food items. So of course, one square foot of rain forest would have substantially more beetle species than a square foot of lawn. Take your field of CT, sure its great for finches, but its about as useful to other non-thistle eating species as a parking lot. And think if something like that happened in a real prairie? *shudder*

You seem like you really care about the local wildlife. So please, if at all possible, for the love of prairies and non-thistle loving birds, do you your level best to get rid of it.

Jessica ~ That Biology Girl ~

    Bookmark   November 11, 2003 at 5:48PM
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Jessica - You made an excellent statement aobut the dangers of CT and other invasive species. Just one little inaccuracy...

Thistle achenes show the classic morphology of wind-dispersed seeds (or in this case, one-seeded dry fruits), rather than dispersing "because of birds". Birds typically distribute seeds enclosed in fleshy fruits such as berries. Seeds with fluffy appendages take to the wind to find new homes. It's safe to say that seeds of the great majority of plant species are NOT distributed by birds.

    Bookmark   November 15, 2003 at 1:20PM
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wayne_5 zone 6a Central Indiana

There used to be a state law in Indiana concerning letting CT go to seed........probably still on the books and enforceable in extreme situations. However it has not been strongly enforced or else CT would not be so rampant here. Oh, if those Russian immigrants had only had seed cleaners up there in the Canadian provinces when they brought their wheat seed over!!!!

Jessica, hello up there in NW Indiana. My daughter lives in White County. I have been up there in Jasper- Pulaski when the Sand Hill cranes were sequestering in the fall. Also keep up the good work at Kankakee Sands.

    Bookmark   December 1, 2003 at 11:38AM
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I have a small wildflower patch and the Canada thistles were looking rather sickly. Decided to investigate on line and found this websie which you might find helpful.

    Bookmark   June 17, 2006 at 7:50PM
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As of 2006 Canada Thistle is a noxious/prohibited weed in the following states:


    Bookmark   June 20, 2006 at 10:42AM
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froggy(z4/5 WI)

agree Kfelice. that is very exciting to read.


    Bookmark   June 24, 2006 at 10:35AM
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Thank you all for posting your excellent information on thistle. I am in the process of purchasing 2 acres of land in southwest South Dakota that is infested with Thistle (assumably canadian)and I now have a very good idea of what I am going to need to do to control it. Problem 1 resolved!

Now if I can just get this kind of info on ridding the 2 acres of the tick infestation, I can rest easy?!

    Bookmark   July 6, 2006 at 3:38AM
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froggy(z4/5 WI)

if u circle ur 'prairie' with a 6ft mow, the inside of that mow should be fairly tick free.

ticks would rather hang out in the tall grass than go thru a mowed area.

just so u dont think u got them bad, im up to 62 ticks on me so far this year. and that is after 40% deet spray.


    Bookmark   July 8, 2006 at 7:25AM
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Yikes. Upon researching the posion, Trimec, I fell upon this disturbing chain of responses to Canadian thistle concern. I found it very unsettling that 'Froggy' whose name has obvious connections to actual, living frogs, was in strong favor of using trimec and/or round-up...both are quite toxic to frogs among other living things. Deet is also very toxic to frogs, among many other things, including human beings; so froggy I suggest you get a more suitable name like frog-killer.
Please be cautious, and aware of the extreme negative effects of using such poisons as herbicides.

Q. What is an effective way to kill thistles?
1. It takes a 20% solution to be effective on thistles and household vinegar is 5% [Editorial Note: Vinegar (acetic acid) as an herbicide has not been identified as an allowable input for BC certified organic production.]
2. Cutting Canada thistle off at the lower end of the stem and pouring water in the hollow stem kills the plant by rotting the root system. If you cut before a heavy rain or use a sprinkler I have found this to be fairly effective.

    Bookmark   July 20, 2006 at 1:55PM
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froggy(z4/5 WI)

omg. ninita is using a computer. i could imagine all the toxic materials in them.

and the next time i have 14 acres of Canada thistle, ill come and invite u to start using ur little household vinegar on it.

by the way, can u show me some actual research on ur claim that DEET, TRIMEC, and Round-Up is " are quite toxic to frogs among other living things" ?


    Bookmark   July 20, 2006 at 8:43PM
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organic broadcaster, a web site with midwest organic farming research, has an article on ct and how researchers pulverize and spray sick ct (it's yellowish) onto healthy ct to infect it and slow it down. round up is not as innocent as it is being portrayed with european research quite opposite of much american. we need to ask who is paying for the research. at my place ct is a haven for pollenators and beetles galore in addition to goldfinches. good luck everybody and may your lives be ct free soon.

    Bookmark   August 1, 2006 at 12:13AM
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Has anyone tried eliminating Canadian Thistle infestations by tilling and re-seeding and/or just pulling them out all the time, and if so, did either method work?

    Bookmark   August 7, 2006 at 3:33PM
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froggy(z4/5 WI)

one would have to till for years and years. how much co2 and other harmfull soil structure problems are u creating? thru tilling that wont work because each little piece makes more CT and u have just created bazillions.

fyi, i was reading that mowing 1 acre of lawn (i assume mowing/ tilling/ anything with a small machine) = pollution of 100000 miles of driving. its because mowers have no emissions vs cars. roundup doesnt sound so bad afterall, eh?

are u really going to try to pull all of them out? if u are, i have acres and acres for u to enjoy urself...

and i have never ever found a prairie that outgrew CT.

and we have discussed the diseased CT, here is a link


Here is a link that might be useful: Al needs to dispose of a lawn and get a prairie

    Bookmark   August 15, 2006 at 9:11PM
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The University of Minnesota finished a study in October '07 concerning pst as a control agent for CT. The pdf on the link below will be of interest to any prairie restorationist battling CT.

I've been doing my own amateur experiments with pst the past 3 years, with modest but increasingly promising results. You can read the log of what I am doing at the link below. Click on "Biological Control of Canada Thistle," once you are at the website.

    Bookmark   June 29, 2008 at 7:46PM
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Hi, I've found really interesting article on how one farmer totally got rid of Canadian Thistle in 3 years for good, using only ecological methods (and in the process'd improved the soil condition):
It describes the method in details. Hope it might help someone.

Here is a link that might be useful: Getting rid of CT

    Bookmark   July 2, 2008 at 11:56PM
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Hey up here in Canada we call that darn stuff Russian Thistle... let's stop blaming the nice Canadians for that nonsense! lol
I'm taking note of all the responses though as it is a challenge to get rid of.

    Bookmark   July 5, 2008 at 7:08PM
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Hey Cheryl, you posted about that darn stuff being Russian rught below a posting of a Russian girl :)
I searched the subject, so these two look completely different. Russian thistle is also being called "Tumbleweed," and "wind witch": or
Also citing on thistles: "Three species of thistles are of greatest concern. Canada thistle (Cirsium arvensis) and bull thistle (Cirsium vulgare) occur throughout Wisconsin and all the North Central states. Musk thistle (Carduus nutans) is common in the south eastern counties plus other "hot spot" areas around the state. Plumeless thistle (Carduus acanthoides) occurs principally in south western and south central areas Wisconsin. Some incorrectly call plumeless thistle by the name "Russia thistle." This can create confusion because another plant's official name is Russian thistle (Salsola kali)."

    Bookmark   September 9, 2008 at 10:13PM
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I professionally managed an urban prairie restoration for a couple of years that was initially overrun with canada thistle. There are a few herbicides that specifically target things in the asteraceae and fabaceae familes that did a great job on thistles. However, for those without the license to buy these chemicals, RoundUp (especially the concentrated powder forms) work wonders.

Mix it up a little stronger than recommended and dribble it into the actively growing tips of the plants. It will keep them from flowering and if they don't die, a second application often does the trick. Like others have said, it will take a few years for every last root to die, but the worst thing you can do is to try and pull them out. They have a rhizome that sends up thistle plants every few inces, pulling the plants can break the rhizome and essentially creates more independent plants.

A friend of mine recommends applying herbicide with 'The Hand of Death'. He takes a chemically resistant glove and puts a worn-out winter cotton glove over the top. He dips his gloved hand into the herbicide and grabs the plants he wants to kill. He says it works like a charm.

And NEVER use wildlife as an excuse to grow invasive weeds. Native animals prefer native plants.

    Bookmark   September 27, 2008 at 3:39PM
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Be careful growing them for any reason! Some states it is not quite legal to allow them to grow unchecked. If they are reported to the right (or wrong) person, depending on which side of the "argument" your on, you could face county extension service out checking it out, and the nasty expense and carelessness of paid individuals who don't care about anything except getting them out of there. And billing and fining you for them and the process of removal.

    Bookmark   October 12, 2008 at 9:57AM
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I use a drill driven weed removal tool called weedspinner that works for me. Saves on my back.

    Bookmark   March 16, 2012 at 2:54PM
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I don't know for sure if mine are Canadian Thistle, but suddenly this year we have low growing thistles all over the yard. This is a yard that children play in, so I need to get it taken care of quickly. I think I will try the Roundup. Wish me luck.

    Bookmark   March 28, 2012 at 1:50PM
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I also meant to add that is my fault. I bought thistle seed for the finches. I wrongly assumed that they irradiate ir something so that it doesn't germinate. I guess it wasn't a good idea to assume. Live and Learn

    Bookmark   March 28, 2012 at 2:00PM
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