A free sample for review! The terminator of the weed world.

It is not in the job description for garden writers that freebies are included. In all my years of garden writing, excluding books for review, I could count such things on the fingers of one hand. I only mention this because I once found out that the wine writer for a provincial newspaper received boxes of samples to his door. I was so jealous.

Imagine my excitement when something arrived. Even more excitable was the accompanying publicity sheet which proclaimed “hasta la vista” to weeds when using (wait for the drum roll) Weed Weapon. Yes folks, I had a convenient spray bottle of weed killer in my hands.

First up, let us be clear. Despite the name of the company that produces this product being Kiwicare, which sounds so wholesome, there is nothing organic about it. It is a new twist on an old standby which is glyphosate (formerly sold only as RoundUp). Forty years of experience tell us that of all the herbicides around, glyphosate is as close to safe as you can get. It could be argued that it has revolutionised the way we think about gardening and lowered our tolerance for weeds. Glyphosate has often been described as the equivalent of a labour unit because you can whip around with a knapsack on your back and cover a large area very quickly.

We use glyphosate here and Mark has always dreaded the day that it may be found dangerous because we could not maintain the standard we want in our garden without it. He has kept an eye on the research and there is no hard evidence that it is damaging or dangerous. This is because it does not accumulate and it breaks down very rapidly on contact with soil or water. It does not cause cancers, it does not appear to harm insect life and basically you would have to swallow a fair amount of it undiluted to cause yourself any harm.

It was a very different story with earlier weed killers. Paraquat was and still is used in some quarters as an alternative to glyphosate. It knocks down plants within hours of application and its environmental bill of health is not too bad. It is also the main tool with which to commit suicide in third world countries because it is cheap, readily available, has no antidote and you need very little in order to cause a deeply unpleasant death. Its dermal toxicity (in other words the ability to be absorbed through the skin) is very high which makes it dangerous for gung-ho home gardeners.

Back to Weed Weapon, which gives the quick hit of Paraquat, apparently without the dangers. One of the problems with glyphosate is that it takes a long time to be sucked into the plant’s system and to kill it. This is temperature related so it can be about seven days in summer and anything up to three weeks in the depths of winter. In that time, some weeds have the capacity to set viable seed. Weed Weapon’s active ingredient remains glyphosate, at 7.2 grams per litre. As far as I can see from Monsanto’s website, this is at the weaker end of dilution rates best suited to quick growing annual weeds and grasses. What makes the difference is the combination with saflufenacil which is a recent addition to the weedkiller range. It is this that gives the knockdown, browning effect on weed leaves within hours. I did a bit of a search on this saflufenacil but the papers Google pulled up were all highly technical and well beyond my very limited high school science. The publicity from Kiwicare blinded me further with science (Protoporphyrinogen Oxidase inhibitor) but it will have been approved for sale by the appropriate New Zealand authorities. It is claimed that it is biodegradable in soil. I mention this because we know glyphosate is but sometimes, when different chemicals are combined, the result can be less predictable than just the sum of the parts.

At least the pesky equisetum is dying

What I can tell you is that Weed Weapon in its ready to use form is perhaps worryingly easy to use. It comes in a squirty bottle like window cleaner. It requires an accurate aim because if you catch other plants, you may kill them too. It certainly knocks down most plants quickly – the dying process is visible within hours. You will be paying for convenience. It retails for around $20 for a one litre squirt bottle. For me, its most useful application is killing out a nasty, invasive equisetum which wriggles out between rock walls but resists being pulled out with its roots. Paraquat users would be well advised to swap to this safer option.

If you are going to use it, you should always wear gloves and not just gardening gloves as shown on the little pic on the back of the pack. Most gardening gloves are absorbent to some degree. You should be using rubber, plastic or latex gloves which you can buy at the supermarket. While it may well be relatively safe to use with low dermal toxicity, good practice says to take precautions. Wearing impermeable gloves is one and never spraying on a windy day is another.

First published in the Waikato Times and reprinted here with their permission.