Herbicides, use, abuse and mis-use

Herbicides help one person do the work of many. But they should be treated like strong medicinal drugs, to deal with a deep-seated problem once and for all. With patience we can do this naturally, with less damage to Earth and a more robust result – but another post for that.

The dividing line – no herbicide | residual herbicide

Sometimes managers are impatient. Recently a herbicide (triclopyr + picloram) proved an enormous problem. Picloram is a residual herbicide (stays active in soil) used to control scrub weeds. Bad advice was given the manager as this chemical acts against many of the plants I intended to use – the assumption was the consultant did not need to be informed – a result of a siloed company culture.

picloram, a billion billion molecules per square metre  – pubchem.ncbi.nlm.nih.gov

As part of design I get to know a site by visiting in different conditions to find micro-climates, opportunities and problem areas. I soon noticed several weeds ‘missing’

  • gorse and broom (Ulex europaeus and Cytisus scoparius – in the Fabaceae or bean family)
  • wild carrot (Daucus carota in family Apiaceae)
  • poroporo (Solanum laciniatum in the Solanaceae – the nightshades)

Plant families are important as herbicides fall into about 25 chemical groups that mainly function along plant family lines. These chemical pathways are very rare – the last decade has unearthed a single new one!

Aciphylla  dieffenbachii  25t 1200px_20Nov.JPG
Aciphylla dieffenbachii – a very rare NZ native plant from the carrot family that had to be removed from plant mix
Gorse Ulex bluff.JPG
Gorse (Ulex) near Bluff, NZ

After some sleuthing it turned out that Grazon DS had been used – this contains picloram and is residual for two-to-five years. Herbicides are registered for specific uses, although as restoration plantings are not part of this process the effect of a given chemical on native shrub species is a matter of educated guesswork, industry friends (and deep searches on Google scholar).

Daucus and erigeron colours 25t P3031570rs.JPG
Wild carrot – although a very colourful form!

Presence of picloram on site resulted in:
– Removal of several species from my planting mixtures
– Redesign of planting plans
– Doubling of project cost (as it nixed an alternative low-cost planting approach)
– A two-year delay in successful plant coverage
– A hold on growing some species at all within a five-year time-frame

This site has 5 millionths of a gram in every square metre: not much but enough to frustrate successful outcomes for many years.

My preference would be to plan ahead with land management, then a site can be planted using natural (and lower cost) means – it is a way we will have to re-learn as weeds evolve to handle our assaults.



8 thoughts on “Herbicides, use, abuse and mis-use

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  1. Most of our most invasive exotic weed specie are not easily killed with herbicide, and certainly not without killing everything around them! I have no problem using herbicides responsibly, but there is not much point to doing so if it is not adequately effective.

      1. That is unfortunately quite surprising for New Zealand. You would think that those there would be more protective of their famously sensitive ecosystem. We are supposedly very protective here, but it does no good when so many of the big ‘landscape maintenance’ companies use so many of the bad sorts of chemicals, and allow unqualified people to apply them. That is part of the reason I needed to leave my last so-called job. The people applying the chemicals were illiterate! Seriously! People applying these hazardous chemicals could neither read the labels, nor document how the chemicals were used! That is illegal, but there is no enforcement.

        1. Same here unfortunately – spray-drift incidents also a big problem) – have been some nasty deaths from illiterate folk working with paraquat. Also a new issue with glyphosate – when I took weed science they said never mix glyphosate in a galvanized tank as you get lots of Hydrogen gas, what they’re finding now is galvanized street poles (lighting, stoplights, bollards) are degraded if glyphosate used to control weeds at their base – http://www.csppacific.co.nz/news/effect-of-weed-killer-on-galvanized-steel-columns

          1. Oh my! All those galvanized poles are out where most of the herbicide gets applied. I keep saying that I have no problem with responsibly applied pesticides, but I also believe in proper horticulture that makes pesticides less necessary! For example, there are so many plants that we should simply not grow because they need to be sprayed with so many chemicals to keep them happy. If we know plants will get mildew in our region, we should simply not grow them, rather than grow them and then give them all the fungicides they need. You know, I have NEVER sprayed my peach tree for peach leaf curl. It was planted in 1985. It gets pruned aggressively in winter so that the new spring grown is more vigorous than the peach leaf curl. Those who do now want to prune peach trees should not grow them!

  2. Thanks Mike – yes pretty complex (it gets political fast too with the agricultural lobby who ‘ve grown used to herbicides and how they reduce labour) and yes the human body is a good analogy, although equally we could be imagined as simply another animal in the forest; every vertebrate is as complex as us in that we depend on, and host, many levels of species. Herbicides (and drugs and synthetic fertilisers) have such wide effects.

  3. Wow. This is a really complicated issue, Nigel. Your opening comparison with medicine makes it somewhat understandable, though, because a lot has been written about the negative consequence of the overprescription of strong antibiotics. I guess in many ways the ecosystem functions like a human body.

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