Sciencemadness Discussion Board

Grass/Weed killer

bquirky - 2-8-2009 at 03:43

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 :)

Eclectic - 2-8-2009 at 04:14

Sodium Chlorate.

Roundup will kill most everything with green leaf exposed, but will not persist at all...


[Edited on 8-2-2009 by Eclectic]

not_important - 2-8-2009 at 05:25

Cover the area with black plastic trap for a couple of weeks. No contamination or leaching to worry about.

dann2 - 2-8-2009 at 06:53


Big flame burner but you will be releasing CO2
Dann2

bquirky - 2-8-2009 at 07:07

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.

not_important - 2-8-2009 at 07:59

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.




Arrhenius - 2-8-2009 at 08:34

Bleach works well for killing algae and moss on brick.

Picric-A - 2-8-2009 at 14:43

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.

kclo4 - 2-8-2009 at 14:59

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.

JohnWW - 2-8-2009 at 15:02

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]

File_Glyphosate-2D-skeletal.png - 17kB

woelen - 2-8-2009 at 22:54

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.

bquirky - 2-8-2009 at 23:55

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 ! :)

kclo4 - 3-8-2009 at 01:32

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.

12AX7 - 3-8-2009 at 06:40

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

Saerynide - 3-8-2009 at 07:53

Pour gasoline and torch it? :D We had these huge cacti that refused to be pulled out and kept growing back when they were chopped. No more cacti now :)

chemrox - 3-8-2009 at 10:42

glyphosate

sparkgap - 4-8-2009 at 22:34

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 (~_~)

Ketone - 5-8-2009 at 07:03

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)

bquirky - 5-8-2009 at 07:43

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.



Neil - 21-6-2011 at 04:31

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.

blogfast25 - 21-6-2011 at 05:57

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.

Arthur Dent - 21-6-2011 at 12:08

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

plante1999 - 21-6-2011 at 16:46

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

Panache - 21-6-2011 at 22:49

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.

Arthur Dent - 22-6-2011 at 03:37

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

Neil - 22-6-2011 at 06:00

Like TSP? You see some people scrubbing off their roof with Tri Sodium Phosphate once every few years and inevitably the moss comes back faster then ever once it gets a hold of the remaining phosphate.

Panache - 23-6-2011 at 20:33

Quote: Originally posted by Arthur Dent  
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


i guarantee that 10% nitric dispersed at around 100mL/m2 will result in surface of the moon barrenness for all eternity, but if you want it unbarren, neutrasliing will result in the phenomena you describe, i imagine your solution to not have been overly acidic and/or ample flushing occured over time..

While we talk about weeds can i ask regarding my lawn, see it's rainy and wintery in melbourne atm, the new lawn i sowed some weeks ago (only about 15m2) initially sprouted nicely but continued growth has proceeded very sluggishly, if i was to give it some love from a couple of merc vapour uv emitters each day for a few hours would i notice a significant improvement or would i be wasting my time? Is temperature more important than anything than anything else is perhaps what i'm asking?

Neil - 24-6-2011 at 05:22

Do you have a speculated route by which the nitric maintains it's moon-death grip?


AJKOER - 24-6-2011 at 20:04

OK, if you want to do make weedkiller yourself cheaply.

Add 2/3 of a bottle of bleach (NaClO) to equal amount of vinegar. Let stand. Add remaining 1/3 bottle of bleach. Done.

For chemist, the acetic acid reacts with the NaClO to form HClO. It also neutralizes the small amount of NaOH in the bleach that hinders the disproportionation of the NaClO into NaClO2 and then NaClO3 (Sodium Chlorate is a commercially used weed killer).

Then, the HClO oxidizes the added NaClO to NaClO3 and is, itself, reduced to HCl.

2 HClO + NaClO --> NaClO3 + 2 HCl

Source: http://www.scribd.com/doc/30121142/Dichlorine-Monoxide-Hypoc...
Page 553

LanthanumK - 25-6-2011 at 02:49

HCl reacts with NaClO3, you know (I hope), so your arrow is backwards to a certain extent. Here are the reactions given on Wikipedia:

HClO3 + HCl → HClO2 + HOCl
HClO3 + HClO2 → 2 ClO2 + Cl2 + 2 H2O
HOCl + HCl → Cl2 + H2O

http://chemistry.about.com/b/2007/09/26/the-killing-power-of...

It works better as a fumigator than a weedkiller. If you want to make NaClO3 without the well-known bleach-vinegar reaction, warm bleach in a corrosion-resistant container until it disproportionates, then use the salty NaClO3 solution. You may selectively crystallize it to get pure NaClO3.

All because a chemical synthesis is shown on a chemistry website does not mean that the average ignorant person will know how to make chlorine safely.

Morgan - 25-6-2011 at 10:31

No surprise.
Roundup: Birth Defects Caused By World's Top-Selling Weedkiller, Scientists Say
http://www.huffingtonpost.com/2011/06/24/roundup-scientists-...