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bquirky
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Grass/Weed killer
Gday Gents,
I have found myself in a situation where i need to poison a large area of brickwork which now resembles a fine lawn
Can anyone think of some substances that a home chemist could use to kill the weeds but not permanently contaminate the soil (or more specifically
leach slowly over time into the surrounding gardens)
Some thoughts
NaCl saturated poolsalt soaked over area. (will leach probobly wont kill efficantly)
CuSO4 More likley to kill weeds but still might soak away.
NaOH Should kill the weeds and eventually react with CO2
Ethanol ???
Ammonia solution ??
Ill now open the floor for discussion 
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Eclectic
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Sodium Chlorate.
Roundup will kill most everything with green leaf exposed, but will not persist at all...
[Edited on 8-2-2009 by Eclectic]
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not_important
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Cover the area with black plastic trap for a couple of weeks. No contamination or leaching to worry about.
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dann2
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Big flame burner but you will be releasing CO2
Dann2
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bquirky
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Flame thrower nice
black plastic is a possibility and just poison the irregular areas ill need alot of plastic though.
The chlorate sounds like a good idea Wikipedia says it can be made by running chlorine through some NaOH so no messing about with anodes.
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not_important
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Unless you live in a wet climate, chlorate is pretty persistent, and if you get much rain chlorate tends to spread.
Flame works well, they sell devices running on bottled gas for that application and farmers use bigger versions on their fields before the crops
sprout. But it will take repeated applications to kill off the determined weeds. There's variants that use steam instead, which might penetrate
between the bricks better.
Slaked lime would be better than NaOH, and could be used after another method killed back the actively growing parts of the weeds, in order to
suppress their recovery. It'll spread out a small amount, so leave a half meter perimeter. It's not going to be toxic to you, unlike copper salts or
chlorate.
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Arrhenius
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Bleach works well for killing algae and moss on brick.
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Picric-A
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Buy a load of roundup. works like a charm...
If not, get a load (depending on how large the are you want to kill is) of bleach, boil it in a glass / SS vessel then spray the resulting NaCl/NaClO3
solution over the lawn.
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kclo4
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Or by other common herbicides used for killing grass. I'm sure you'd be able to find various ones at a farmers market. I would think it would be more
practical to buy a commercial grass poison then to use some inorganic salt that would likely spread.
You could buy those big black garbage bags and cut them open, or a tarp to kill the grass with.
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JohnWW
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The long-term problem would be regrowth from dormant seeds in the crevices, even after using a black plastic sheet or a non-residual general herbicide
like Roundup ("glyphosate" or N-(phosphonomethyl) glycine , see http://en.wikipedia.org/wiki/Roundup and http://en.wikipedia.org/wiki/Glyphosate ).
However, Roundup cannot kill seeds, or red clover and some other "Roundup-resistant" plants which are mostly legumes and genetically-engineered
plants. Use of a flamethrower would kill the seeds, and also mosses and lichens. Alternatively, a residual and general herbicide that can kill seeds,
including new seeds for several months afterwards, is Simazine, a triazine derivative, but it is now banned in the EU; see http://en.wikipedia.org/wiki/Simazine
[Edited on 2-8-09 by JohnWW]
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woelen
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If the area is not too large, you could use boiling hot water and pour that over the area. The hot water seeps into the ground and also kills roots
and seeds up to a few cm depth. I myself have used this method succesfully for killing unwanted grass and other green stuff.
This is an environmentally friendly method, which does not leave any chemical residue. Of course, when the area is very large, then you need a lot of
hot water and then this is less practical.
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bquirky
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The area is about 30m x 50m so 1500m^2 and is fairly irregular with poles all over etc.
i guess im going to require a lot of whatever i end up using !
although lime is sounding good for the areas well away from the gardens and then perhaps comercal weed killer for the more detailed area.
perhaps i should use all of the methods mentioned in different areas and compare the results !
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kclo4
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Are you able to prevent it from getting water? Where I live grass is difficult to keep alive in the summer. If you could kill it via dehydration and
burn it away, you'd probably be in pretty good shape. It would grow back each year, but if you could redirect say.. the irrigation, you'd only have to
burn it away once a year, or so.
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12AX7
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If it has to stay weedless, plant a hardy grass to keep them choked out. Or let the weeds plant it, and keep them mowed down so they don't look ugly
(if mowing is possible, given the "poles" all over). Any vegetation will hold off soil erosion. If it has to stay clear of any vegetation, lay down
gravel or pavement, some sort of surface inhospitable to weeds.
Tim
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Saerynide
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Pour gasoline and torch it?  We had these huge cacti that refused to be pulled
out and kept growing back when they were chopped. No more cacti now
"Microsoft reserves the right at all times to monitor communications on the Service and disclose any information Microsoft deems necessary to...
satisfy any applicable law, regulation or legal process"
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chemrox
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glyphosate
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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sparkgap
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Yes, glyphosate, and please please please don't even consider any of the triazines (atrazine, simazine and ilk).
Bu I must ask first, though, how much rain has there been in your part lately?
sparky (~_~)
"What's UTFSE? I keep hearing about it, but I can't be arsed to search for the answer..."
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Ketone
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What about copper hydroxide?
"Should" (but I'm not into gardening so I can't say for sure) work as well as CuSO4.. But since it's practically insoluble in water it shouldn't leech
into the ground.. atleast not much. (And neither should any CuCO3 that might result from it's reaction with CO2)
It's also easy to make.. and should be easy to apply, even between the cracks.
I'd personally never use Roundup, there's serious questions about just how toxic it is..
(Not to mention that Monsanto are a bunch of assholes, but that's another story)
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bquirky
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yeah we just had a few weeks of rain. but its normally very very dry the issue for me is mainly the fire risk of the dry grass/weeds so i want to sort
them out before fire season.
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Neil
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bump
20% acetic acid, spray it on in full sun on a hot day. It's like VX for plants.
You also get to see blue flowers turn red.
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blogfast25
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The ones that contain (3 %) pelargonic acid (nonanoic acid) or ‘a blend of fatty acids’ (usually C8 + C9) are reported to work well and are fairly
environmentally friendly. They smell slightly (a bit goat cheesy, dieselish) and would probably deter pets.
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Arthur Dent
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Plain ol' vinegar in a spray bottle is absolutely excellent to kill grass between bricks on my driveway and totally non toxic. In a day and a half
after application, the grass and weeds begin to whither. It's sometimes the simplest things that are the most efficient. Leaves nearly no trace, aside
from a slight efflorescence on the stones, which washes away when it rains. A trick taught by my dad.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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plante1999
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10% NaOCl sol. , efficient and not persistan , does not contamine the area because it react/and/or/dissolve , need a climate that have hot day an very
rainy day , apply when sunlight is present.
this appen when sunligth is present ( to distill of the water)
3NaOCl -) 2NaCl + NaClO3
I never asked for this.
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Panache
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nitric acid, 10%, keeping note of the volume used, followed by a neutralizing equivalent of bicarb some time later or never if area is never to be
inhabited by plants again.
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Arthur Dent
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Nitric acid? Wouldn't this promote the growth of weeds and grass by supplying ample amounts of nitrates?
I remember some 20 years ago, I discarded a small amount of ammonium nitrate and nitric acid mixture by throwing it down a sewer that was surrounded
by grass. A little bit of the mix fell on the edge, effectively melting off the vegetation and killing it good.
But a year later, the same edge of the sewer hole was surrounded by thick, luxurious grass that grew nearly 10 times faster than the surrounding lawn.
This phenomenon lasted for a good 3 or 4 years...
Personally, I would avoid anything containing nitric acid, as this might kill the weeds on the spot, but will probably promote growth at a later date.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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