
Get a cheap paint brush, some vinegar, (10% is favorite with some, although you can find 20%. I never use 20%, nor, for that matter, 10%. Frankly, I only use 5%), and paint it on the foilage. Sun and vinegar work together: no more invasives.

I would caution on a couple of things, however.

Use protection for strong acidic solutions. Strong solutions are not safe for unprotected skin or any other surface: let's all remember the reasons medicinal and preservative solutions are effective for their purpose.

Second: paint brushes put the killing factor (the acid) on the foilage, rather than the soil, but that certainly doesn't mean the acid won't get to the soil, if allowed. Use Good Judgement, Please. Do Not Overdo.

The acidity of the vinegar, along with the action of sunlight, has a synergistic effect.  With judicious use of the two in conjunction, one may eradicate many unwanted plants without harming other plants, or the mother soil. That last may be a fine thing to consider, if one is  hoping not to "kill" a plant, but rather "relocate" it, via rhizome, root, or seed, and is hoping to keep the soil well able to grow the preferred flora in its place.
 
Shucks, folk. Even Kudzu has it's purpose. Why was it introduced from the orient to the americas in the first place?  <G> 

Here's the deal: 

The reason for the paintbrush is you do *not* want the vinegar to go anywhere you don't intend it to. Certainly, not to the soil. 

Some will say you need 10 or 20% acidic vinegar. I find simple 5% fine for my purposes. If working on a big bad nasty, I'll add a bit of salt in the mix and stand back for a minute or two.

  Use the strength you find effective for your purposes. To be honest, I have only heard of strong-strength acidity being better;I have not used it myself. Just haven't seen the need, nor the availability. I still like my plain old 5%.  Even works on multiflora rose!   

10% acidity is usually called "canning" vinegar, at least in the mid-areas if the U.S.

Please do bear in mind though: 

Anything that will kill one plant will most likely kill others, and only individual pull-n-sterilizing will do the job easily, or within a season or 5. 

Mom Earth does know what she's doing, she keeps hoping we will learn from her patience and knowledge. {;)  

If one is cultivating medicinals on a commercial, large, or non-native habitat basis, I have no answers as to why physical barriers haven't worked unless it's from misunderstanding of the process. I expect those to be first defense (?). Wow: frankly, if those haven't worked well, I'm  out of my league. 

Wouldn't be the first time. {:)   deb

--- MPWG-request@lists.plantconservation.org wrote:
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Message: 1
Date: Thu, 1 Jul 2004 15:08:22 -0400
From: Patricia_DeAngelis@fws.gov
Subject: [MPWG] Question of the month: Invasives removal amidst
	harvestable	medicinals
To: mpwg@lists.plantconservation.org
Message-ID:
	<OFED0436E4.FDC43B96-ON85256EC2.003FEA16-85256EC4.00692345@irm.r9.fws.gov>
	
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Here's the first installment of what I hope will be a regular monthly
affair - The Question of the Month.  This month's question came about as a
result of questions from you - the MPWG listserve!

The Question:
When plant invasions are beyond mechanical means of control (i.e. hand
pulling), are there any chemical methods of control that can be used and
still allow one to continue to harvest medicinals (or other plants for
human consumption) or, better yet, to retain "organic" status?


