Monday, 3 September 2012

Using glyphosate

After I took early retirement, clients would often employ me to eliminate perennial weeds such as couch, ground elder and bindweed from their gardens. The easier commissions were when the gardens had been totally neglected. The weeds were intact! Much harder was when gardeners had scrabbled away chopping out weeds. Glyphosate only kills through the leaves of the growing plant, the more luxuriant the growth the better. No use zapping convolvulus as soon as it pops out of the ground, better that it’s six foot high.


My Nimbus 2000 broomstick with its extendable wand. 
Must not be flown in windy conditions.
If you are going to use glyphosate in a large garden, get a professional knapsack sprayer. One with a long lance will make spraying easy and precise. It will cost you £120 (here in the UK) or so but will last for years. Of course, this is not essential. I originally sprayed away coarse vegetation in Bolton Percy cemetery with a hired knapsack sprayer, and subsequently, for many years only used a small hand sprayer.

Contrary to opinion, glyphosate can be used at any time of the year. The critical factor is that the weed must have living green growth. In the winter months, many perennial weeds are dormant and it is useless to spray. I have, however, sprayed green couch grass in late November, with complete success. Weeds emerge from seed throughout the year. If they are growing, they can be sprayed, and I do so all year round.  In winter, weeds will take six or more weeks to die, but who cares as they fade away. It is particularly useful to spray in autumn and winter when the soil is too wet for hoeing and garden plants are dormant.

Standard advise on the can is that six hours must lapse before any rain. This is correct for thick weed cover. For difficult perennial weeds, a day or more is even better. Usually my own ‘spot spraying’ is of seedling weeds. If rain does not immediately threaten, I just go out and spray. Over thirty years I have sometimes been caught out, but if it stays rain-free for an hour, I have not wasted my time.

A curious consequence that I have observed, is that if rain is very light and lasts only a few minutes, it actually enhances glyphosate’s effect on small weeds. Young plants capture precious rain and by a process of ‘stem flow’, channel it to thirsty absorbing roots at the base of plant. Within a very short while, of course, glyphosate in the soil will be broken down by bacteria and will leave no residue.

18 comments:

  1. Surfactant-loaded formulations are convenient, but the downside is that they can possibly kill aquatic life. A surfactant-free glyphosate product (one that is at least 40% glyphosate in the form of its isopropylamine salt) can be used for most applications and will not harm fish, amphibians or wildlife. Unfortunately it can be difficult to tell whether a product contains a surfactant, as these and other additives are lumped under Inert Ingredients. In the USA there are many surfactant free products but I am not sure if this is the case in the UK?

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    1. Lewis Starkey, Penn State5 September 2012 at 14:17

      I agree about the low toxicity of Glyphosate. Soil microorganisms quickly break down surfactant-free glyphosate into non-threatening phosphorus and amino acids that, despite the scare stories about eating Frankenstein food, present no danger to humans, insects, wildlife or amphibians.

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    2. Roy Sinclair, Snettisham5 September 2012 at 15:55

      I use Glyphosate in the delicate environment of the Norfolk Broads and have to agree with this comment. The bird, amphibian and fish life in the area sprayed is healthy, plentiful, diverse and increasing.

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    3. The greatest danger to frogs in my garden is stepping on them. They are everywhere! They particularly like to hide in my small nursery. Every time I water they jump swiftly away.

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    4. I find Helen’s comments particularly interesting. I know that Rodeo and Accord are US products that are glyphosate-only. In the UK, glyphosate is combined with surfactants and adjuvants, chemicals (wetting agents) that are mixed in to assist in the delivery. These are, indeed, not listed on packaging. I know (I may be wrong) of no commercial formula that is surfactant-free on sale in the UK.

      However, I HAVE noticed, when using glyphosate here in the UK, that all plants are not equal, Roses and hedging plants, especially, weaken and do not thrive after applying glyphosate even close by (not directly). I am wondering if the glyphosate/surfactant formula is having a detrimental effect on hedging because soil microorganisms, which should be breaking the glyphosate down, are much less plentiful in the poorer soil in which hedges grow. I have no explanation for the susceptibility of roses.

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    5. Tess, I find your comments fascinating, as we have noticed the exact same phenomena regarding both roses and hedging. My husband has always used glyphosate along the hedgeline, but now many of plants fail to thrive. This is a hedge that has been in for many years. The possibility that the poor soil under the hedge does not have the micro-organisms to cope with breaking down glyphosate is one I had not thought of. The rose is from the same family as many hedge plants - perhaps that has a bearing too?

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    6. Reply to Helen's first comment
      I am not aware of any surfactant free formulations available in the UK. Many of the readers of this blog are home gardeners and the range of glyphosate products to amateurs in this country is very narrow. Our authorities keep amateur and professional products separate. Garden centre glyphosate is weak and expensive, commercial glyphosate is more concentrated and a fraction of the cost.

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  2. One of the most articulate commentators on the subject of Glyphosate is Jeff Gillman, a professor of horticulture at the University of Minnesota. His excellent book, The Truth About Organic Gardening, exposes much of the current scaremongering studies on Glyphosate as not being supported by scientific research.

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    1. Thanks for this. I have just googled Jeff Gillman. He's the kind of horticulturist I most admire.

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  3. Packaging seldom informs the public of what these additional chemicals are. Most of the information that is to be had on the deleterious effects of this herbicide on fish, frogs, soil biota, and human beings is based on research using the Roundup (with surfactants) formulation. It is often unclear whether researchers have used only glyphosate, or a surfactant mix formulation. The two are VERY different products and have VERY different properties. The addition of the surfactant makes the formulation many times more toxic to other biota with which it may come in contact. Cationic Surfactants, especially, have been shown to increase the efficacy of glyphosate, so it is not surprising that herbicide manufacturers favor it.

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  4. In reply to Tess and Cathi, I have never found hedges suffer from glyphosate spraying, even when I admit to being not over careful. In my experience the soil at hedge bases is no more infertile and lacking in bacterial activity than any other part of a garden.
    What I do frequently find is that if a plant is sick in a garden where spraying has taken place the weedkiller always gets the blame!
    So many things can adversely affect plant growth. I know in Cathi’s garden (she is a neighbour) that her garden is subject to dramatic changes in water table levels and sometimes drought conditions. The decline of her hedge is more likely from this cause than glyphosate spraying.
    As to roses, I find some roses are extremely sensitive to misdirected glyphosate and yet others are remarkably resistant. I tried to kill a rose a few years ago with two top strength sprays. It did not turn a hair. It has now been reprieved and is a very fine specimen!
    I have similarly been caught out with brambles (wild blackberries) which refuse to be killed by spraying and yet certain cultivated varieties have proved remarkably sensitive! Often damage on woody plants shows up in new growth in the following season.

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    1. Oscar Jensen, Wisley6 September 2012 at 14:49

      I think that there may be something in what Tess and Cathi have observed. There has been much new and interesting research done on glomalin and how mycorrhizal fungi extend beyond roots, affecting plants quite a distance away. I suspect that most of the glyphosate trials were conducted when nothing was known on this matter, and it could well be very relevant. Mycorrhizal fungi and their production of glomalin is known to be affected by temperature and moisture so, if what you say about Cathi’s garden is accurate, this could be another factor in how the soil copes with Glyphosate and surfactants. Like Tess, I am unaware of surfactant-free glyphosate in the UK, professional or otherwise.

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    2. A little glyphosate is good, a lot is NOT necessarily better.
      It’s been found that it is possible to chemically burn plants before glyphosate has been delivered into the plant body. Plants treated in this way are able to re-sprout from their roots.
      On the matter of surfactants and their effect on insects and amphibians, in the US, many foresters and nature groups just use glyphosate-only products, or those with aquatic-safe surfactants.

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    3. When I mentioned using 'top strength' sprays I was still spraying within the recommended range. I am aware that using many herbicides at extra high dose defeats the object of translocation by causing burning contact action. I must admit though I was unaware that this had been shown to apply to glyphosate. Thanks for the information Maryann

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    4. Thanks Oscar for your interesting reply. I am extremely excited about the discovery of glomalin and I have been planning for some time to post on this topic. I wonder if mycorrhiza which have been shown to make contacts through the soil from plant to plant might possibly shift glyphosate itself, from one plant to another.When I ever so carefully dab a coarse grass weed in my lawn with glyphosate, fine surrounding fescue grasses also die! I am either not as accurate as I think or some biological transfer of glyphosate is taking place.

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  5. Oscar Jensen, Wisley7 September 2012 at 10:51

    The discovery of glomalin over a decade ago excited not only soil biologists. The biggest question since, has been why AMF produce it. Little was known about the compound’s ecophysiology. However, research from universities in Sweden and Berlin last year has shed some light, suggesting glomalin production may be a stress response. They set up experiments to test for mechanical stress, water stress and salinity stress. Elevated salinity is caused even in non-saline soils as the soil solution becomes more concentrated during drying. The latter both showed significant changes to the control, causing altered growth morphology. All this could be very significant to the surfactant debate and cannot be dismissed.

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  6. You are right Oscar. Petroleum based surfactants are now being seen as more and more of a problem, and not just in soil ecology and horticulture. To counter this, a team in Peoria have set their sights on developing a ‘green’ surfactant from naturally occurring yeasts. Sophorolipid production from the candida species was especially high yielding and will now be investigated further.

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    1. Oscar Jensen, Wisley7 September 2012 at 15:55

      Indeed Maryann, I believe I read their paper in FEMS Microbiology Letters and it was most interesting. Apparently they discovered a completely new candida yeast that will be added to the shortlist of candidate yeasts with potential for use in large scale fermentation-based methods of mass-producing sophorolipids as alternatives to surfactants. This can only be a good thing.

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