How to Kill Weeds

Weeds are a lot easier to kill than you may think, like flies and cockroaches.

In just the same way that many things other than insecticides will kill pests, many things other than herbicides will kill weeds.

The reason is not too hard to understand – weeds, and any plant for that matter – are carbohydrates. As well as that, they have vesicles and cells that are dependent upon delicate ionic and pH balances.
If you use glyphosate or other systemic herbicides, it takes the best part of a week for it to start working, which is often perceived as being too long.

So go into your cleaning cupboard and see what you’ve got. Any cleaner is usually alkaline or acidic, and most of them will work. What do you have – Ajax Spray & Wipe with lactic acid? That’ll do. Bam Easy Off with sulphamic acid? Yep. An oven cleaner (caustic or non-caustic)? Sure thing.

Any of these things will do the job. The only difference between these cleaning chemicals and the herbicides is the amount you will need to use – with a herbicide a light misting on the leaves will kill the plant, whereas with a cleaning chemical a more significant dousing will be required.

An excellent option that is now being used in some products (along with a herbicide) is acetic acid (vinegar). Get yourself a 5L garden sprayer, tip in a cheap bottle of vinegar, top it up, and give your weeds a dousing, and the weed will curl up and die in a day or two.

Or if you want to do it quicker, use either an oven cleaner, or hydrochloric acid (1:10 will do it).

Btw, I’m not a great fan of glyphosate (roundup, zero). It’s not strong enough. A far more potent product are the once-a-year weeders

Ammonium Nitrate: the Jekyll and Hyde Chemical

Chemistry contains a few Jekyll and Hydes.

There are chemicals, like DDT, that are capable of achieving great good and great evil.  At the top of this list is ammonium nitrate.

In the early years of the 20th century, the world had a problem.  Fertilisers were hard to make.  The only source of saltpetre, the chemical that was used as the basis of most fertilisers, was in Chile.  Digging it out, and transporting it around the world, was an expensive and time-consuming process.

The problem was the nitrogen.  Nitrogen is required to make nitrates, and of course ammonium nitrate, which contains two nitrogen atoms.

And while there is plenty of it around us – the air we breathe is 70% nitrogen – no one had worked out a way to get it out of the air, and so the only way left was digging it out of the ground in Chile.

Along came Fritz Haber.

Haber worked out a way to get nitrogen out of the air, and convert it to nitrates.  And so suddenly the world had a plentiful and cheap supply of fertiliser, and vast tracts of land could be made arable, and millions of people could be fed.

That is the Dr Jekyll part.

This all happened in 1913, which you may notice was the year before the First World War started.

As it happened, the Germans had another problem.  Explosives.  They couldn’t make them in any great amount, because they were nitrate-based, and the British had cut off their supply of saltpetre from Chile.  The only source they had was urine and bird droppings, which was never going to yield much.

Suddenly, as if by magic, along came the Haber process.  Suddenly, now the Germans had a plentiful supply of nitrates, and they could make as many explosives as they wanted.

That is the Mr Hyde part.

In fairness to Haber, who developed it as a fertiliser, he was not to know that this chemical would be used to make the explosives that were killing millions of people. But let’s be realistic about this – were it not for the Haber process, World War I would not be what it was – the British would have had the ability to make explosives, and the Germans wouldn’t, and the war would have been much, much shorter.

And today the ammonium nitrate is used for both sources.  It is used by terrorists, and it is used by mines as an explosive.  It is also used by farmers as a fertiliser.

Incidentally, although it was known as explosive compound, this knowledge was not very widely disseminated, and it led to the second greatest industrial accident of all time.

In fact, it has led to a few industrial accidents – in years gone by, before people knew how explosive it was, they would actually break it up with a hammer and chisel if it had caked together.

Are My Chooks Eating DDT?

A listener asks:

“I live in an older suburb in Perth (Freo) in the past they have used chemicals in the ground (DDT) will growing vegetables at home even having chickens at home will any toxic chemicals that had been used in the past be found in the vegetables eggs etc….Thanks have a great day”
Tony from Freo

It’s a good question.

DDT spread quickly in popularity after World War II, and was eventually used right across the world, including Australia.  It was an incredibly effective insecticide, wiping out mosquitoes bearing malaria, and in doing so has saved millions of lives.

Unfortunately, it also affected marine life and birds, and in a massive overreaction, it was banned in 1972 in the US, and 1987 in Australia.

The ban was lifted in 2006, and it is now being used in Third World countries where no alternative is available.  It’s a bit of a funny one, as neither its effectiveness in saving lives, or its impact on marine life and birds are called into question.  So in a way it is hero and villain at the same time.

The problem with it is that it is an organochlorine insecticide, and as such it is essentially nonbiodegradable.  It’s half life is something like 50 years – compare that with the half life of modern day insecticides like pyrethrins, which are measured in months.

So to come to the original question – is it possible that we may have DDT in our soils, if we live in an area where it was used in the past?  The answer is that yes it is a possibility.

To answer Tony’s specific question, his chooks may be able to help.  One of the effects of DDT in birds, is that it results in eggs being laid with weak shells – so weak, for example, that they often break when their mother sits on them.  So if the eggs that Tony’s chooks lay appear okay, there is every chance that there is minimal DDT in his soil.

But if you want to be sure, there are three labs in Perth that can test a soil sample for you: SGS in Newburn, ALS in Malaga, and the Chemistry Centre in Bentley.

It’s a Whitewash !!

One of my earliest childhood memories was a job that I had remarking the white lines on the local tennis court.

My recollections  are that I had to mix up a fine white powder with water, pour it into this weird looking three wheeled contraption, pump it up with a hand pump, and then as I walked down the lines pull on a lever which squirted the white stuff onto the line.

This was, of course, whitewash – at least one form of it.  In years gone by, before sophisticated paint formulas had been developed, and before pastels had even been thought of, people used whitewash to paint just about everything, but mostly houses and fences.

So what is whitewash?  Well of course we have all read about Tom Sawyer and his famous account of tricking people into whitewashing the fence.  But we aren’t told how Tom Sawyer made up his whitewash.

Mostly, whitewash appears to be hydrated lime. According to Wikipedia, it is a mixture of hydrated lime and calcite (which is limestone, or calcium carbonate).  The idea is that when you paint it on, the hydrated lime reacts with carbon dioxide in the atmosphere and is converted to calcium carbonate (limestone), and the mixture hardens, or cures.

Ca(OH)2 (lime) + CO2 = CaCO3 (limestone)

The trouble is that I don’t know anywhere where you can buy calcite, or chalk as it is commonly known, in powdered form.  So that leaves us just with the lime, which I’m pretty sure is what I put on the tennis court. But the problem with this is that it will take longer to cure than it would if it already have some calcite in it.

So how do we make it up?  Fortunately, our friends at Cockburn cement can help us out.  They have produced a series of formulae for use in different applications. The one for cement looks particularly interesting, and would probably be a nice way to finish the surface after cleaning off oil stains.  I’m not sure why they put salt in there, but it’s probably used as a thickening agent to help the lime stay in suspension, and make it easier to get a consistent coating when you paint it.

If your cement driveway needs rejuvenating, give it a go and let me now how you got on.