In article , "Carolyn LeCrone"
wrote:

A neighbor uses vinegar to kill weeds growing in cracks in the street and
sidewalk. Does the vinegar degrade? Are there long term negative affects?
Carolyn

The acetic acid in vinegar is highly caustic & commonly recommended as an
organic herbicide. It is also used to acidify overly alkaline soil, though
such chemical tinkering with the soil has a bad accumulative effect & it
is better to acidify soil with compost or peat.

Acetic acid is non-selective & kills everything. At solutions rich enough
to kill plants it will also acidify the soil far more than is good for
plants or healthful microorganisms. Kitchen vinegar is 5% acetic acid
which is very mild (acetic acid can kill even people but obviously at such
dilute strengths it is a safe part of the average family diet). 5%
solutions might not be strong enough for the toughest sorts of mature
weeds though its adequate for seedling weeds & anything sensitive. A 20%
acetic acid solution would kill everything within two hours of contact,
but could also be harmful to skin contact; I wouldn't recommend looking
for a stronger source than kitchen vinegar, but there are horticultural
grades of acetic acid that are even stronger than necessary, 25% acetic
acid, which could really do a number on your lawn if you're sick of all
that greenery.

I wouldn't ordinarily use it since it is harmful to everything it touches,
but cracks in the street or sidewalk might be a reasonable exception. I
really prefer manual removal of weeds & topcoating with composted manure
which suppresses germination of weeds' seeds while benifiting all the
wanted plants, but if a herbicide were REALLY necessary, I'd consider
vinegar.

The USDA's Agricultural Research Service (ARS) did the first field &
greenhouse analyses of vinegar as an organic herbicide specifically so
that organic farmers would know for certain it had no negative effect on
crops. Spot-treatment in cornfields, one weed at a time, was effective in
eradicating the majority of all the most aggressive weeds, with no ill
effeccts to the corn so long as the corn was not also sprayed. It was
found useful for pre- & post-crop weed suppressant to stop new weeds from
emerging. But there is always danger to plants because it just as rapidly
injures desirable plants & can only be sprayed on absolutely windless days
in circumstances that do not risk accidentally killing everything else in
addition to the weeds.

Here's an article on the topic:
http://www.hort.purdue.edu/ext/vinegar.html
and here's the Agricuoltural Research Service press release:
http://www.ars.usda.gov/is/pr/2002/020515.htm

Cornell University did follow-up studies to the USDA research, the major
findings noted he
http://www.cce.cornell.edu/rensselae..._herbicide.htm

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
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