To Spray or Not to Spray? 

That is the Question.

by M. J. Harvey  September 2004


From a brief note this piece has grown into a wide-ranging polemic so let me introduce it with a short biography to explain where I am coming from.  I started my undergraduate career at King’s College in Newcastle upon Tyne (now the University of Newcastle upon Tyne) intending to take a degree in chemistry.  But my grandfather and parents had given me a love of plants and I switched at the end of my first year to the Department of Botany which happened at the time to be a centre for plant physiology and biochemistry.  I left with a degree in Botany with a minor in microbiology.  So although my friends think of me as a botanist in the 18th Century Linnean sense I have always kept up my background interest in what goes on inside cells and in plant chemistry.  What follows is a perspective derived from a lifetime of study of plants, chemistry and history.


In my early years in Halifax NS, universities were in a state of rapid expansion (one even hired me), and we occasionally got a little money from the Graduate Faculty to invite distinguished researchers to visit, give a public lecture and commune with graduate students.  One of these speakers – and after nearly 40 years his name has gone from my brain – was one of the pioneers in plant physiology, doing research in plant hormones – the auxins.


Now I won’t try to recite the details of the talk but during questions at the end of the lecture he remarked that he had been surprised to find out later how early in his research the US Department of Defence had been abstracting his research papers.  This had significance for the Vietnam War and influences us to this day but before I get into that let me give a brief summary of auxin chemistry.


Auxin is indole acetic acid (IAA) and is responsible for plant growth primarily involving cell expansion.  It is produced in the growing shoot tip and acts differently on shoots and roots, inhibiting the growth of side shoots and hence responsible for apical dominance (pinch out the shoot tip and the side buds grow out), but stimulating root growth.  The first practical application of this was in producing rooting hormones but not in the IA form since if you say “Boo” to it, it decomposes.  For commercial rooting compounds simple substituted molecules where the acetic component is replaced by butyric or naphthalenic groups are used (IBA, INA).  These can be left on the greenhouse shelf without going off.  Here we have a bit of abstract plant research helping the horticulture industry and amateurs by greatly facilitating the rooting of cuttings. 


The next tangent I want to go off on is our fondness for chlorine.  And I do not refer to chlorine in the form off chloride ions as in table salt, I mean the free form, the stinky gas which can be smelt as the disinfectant in most swimming pools.  As a civilization we are in love with chlorine and produce millions of tons each year.  A reactive element, chlorine can be incorporated into many chemicals.  Its industrial uses are many, from plastics such as polyvinyl chloride to its direct use as a powerful disinfectant used to kill bacteria in water supplies and sewage effluent.


Curiously, chlorine is rarely found in natural organic molecules – only the antibiotic chloromycin (chloramphenicol, Parke-Davis 1947) comes to mind.  The chlorine atom is large compared to carbon, oxygen and hydrogen which comprise most natural organic molecules.  The effect of adding a chlorine atom to a molecule is to render it lumpy – the chlorine atom literally sticks out.  This effect has the result that when a chlorine atom is added to an otherwise normal biological molecule the usual enzymes which would have acted on the molecule no longer work – they do not recognize the chlorinated molecule – it is the wrong shape.


This stability of chlorinated molecules was an enormous advantage and led to the development of some wonderful insecticides such as DDT (Geigy, Switzerland, 1942), Gammexane (ICI, UK, 1947), Chlordane and Lindane which were really good at killing insects and which lasted on the plants or in the soil thus saving labour in not requiring repeated applications.  These compounds had much lower acute toxicity to the workers applying them than the older insecticides such as the arsenic compounds and nicotine previously used.


There was only one problem in the above scenario, the very advantage that these products had – stability – eventually became their drawback since they found their way into places no one anticipated and had unexpected effects on non-target organisms, including humans.  The a quiet little lady living in the Maine coast published a book, Silent Spring, and gradually, very gradually, people started to question what we were doing to the ecosystem.  The author, Rachel Carlson, became an international celebrity.  From this point on the chemical companies producing these chemicals came under attack.


To continue on the auxin story, it was rapidly discovered that when plants were treated with an overdose of auxin their cells over-expanded, the shoots became distorted and the plants collapsed.  Auxin analogues stabilized with chlorine were synthesized and found to act on plant cells at very low concentrations.  One of these, 2,4-D (2,4dichlorophenoxyacetic acid), turned out to be active, non-toxic to humans and, moreover, was selective in its effects on plants – at the right concentration it killed broad-leaved plants but not grasses.  Here was one of the futuristic predictions of the 1920’s and 30’s come true – the self-weeding lawn – and manufacturers of daisy grubbers (those forked utensils used to root out dandelions by hand) joined buggy-whip makers in the unemployment line.


So by the late 1940’s we were using less horse manure in our gardens because there were fewer horses, the ambition of middle and even lower-class families to own a car started to become feasible, bicycles became kids toys instead of a universal means of transport alongside buses and trains and we were on our way to a brave new chemical world.  Where this went wrong, the influence of the Vietnam War, the reaction of the chemical industry and the rise of the organic movement will be dealt with in a continuing article.