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Time to repeal the noxious weeds act

Full version of letter to Irish Farmer Journal printed 6 October 2007

The Minister for Agriculture’s recent public reminders of landowner’s responsibilities under the noxious weeds act has seen a flurry of letters and comments on the issue; unfortunately, despite the heat little light is being shed.  Much of the current debate is rooted in the kind of thinking that created the Act in 1936, thinking that is so far from current scientific understanding and the need for environmental protection, that at best it looks ridiculous.  The attitude of the time was one of man vs. nature, weed scientists called for the eradication of weeds, war was declared and the weapons of choice were the new fangled herbicides.  Over half a century later, we are now loosing the war on weeds.  Until the 1980s, weed science journals were dominated by herbicide research.  Then a new issue started to creep in, herbicide resistance, then it flooded in.  Herbicide resistance is flaring up like wild fires across the world.  In the West Australian wheat belt, they now have multiple genera of weeds that are resistance to multiple classes of herbicides.  They have simply run out of herbicides. 

The last fifteen years has seen a wholesale, and long overdue, revolution in weed science, Integrated Weed Management (IWM) is now considered the only effective way forward.  Chemical herbicides are only one of the four legs of the IWM stool; physical, cultural and biological weed management methods are now essential to prop up failing herbicides.  Weeds are also no longer seen as an enemy to wage a war against.  Weed science has dropped ‘weed control’ for ‘weed management’ in recognition that we will never control, let alone eliminate agricultural weeds. 

Weeds clearly have the potential to dramatically reduce yields if no action is taking against them.  However, they only need to be managed so far as to minimise harm, e.g., yield losses or introducing poisons into food.  Weeds are vital component of agricultural biodiversity, and many of the environmental issues that REPS aims to address are directly caused by over zealous use of herbicides.  The DAFF is Janus like in this respect; one mouth is calling for increased biodiversity, while the other mouth is calling for the destruction of biodiversity. 

None of the reasons the Minister gives for destroying the likes of ragwort, thistle, dock, male wild hop and spring wild oat have good scientific basis.  The unifying attribute of these weeds is they are visually obvious.  They stick out of pastures and above crops in a way many consider unsightly.  Ugliness is no reason to control weeds and there are a wide range of non-visual weeds e.g., scutch, that cause greater yield loss and would be more deserving of a place on the list.  Ugly is also in the eye of the beholder, ragwort was introduced as a pretty garden plant.

The unspoken rationale of the act is that if only all landowners destroyed these weeds in a concerted effort then Ireland would be rid of them forever.  Why else the overbearing enforcement requirement of the act?  Such a belief is pure nonsense; while it is theoretically possible to eliminate a plant species from an island, it is impossible for the species on the list.  There are far too many wild areas in Ireland for this to be achieved.  Nor is it desirable.  Docks, for example, are a native species of Ireland and are an important food resource for the green dock beetle, an emerald jewel of a creature.  Eliminate docks, decimate the beetle, yet more biodiversity loss. 

I fail to see why we need an Act of Parliament to tell farmers that some weeds are toxic to stock and others cause yield loss.  It is in a farmers own financial interest to manage all the weeds on his farm to maximise his output and animals health.  If the Act was not there does the government think farmers will suddenly allow ragwort to grow in their pastures and poison their stock?  The idea that weed seed is widely dispersed is also erroneous.  Research shows that even for species with airborne seeds, the vast majority of seeds only travel a few meters from their parent plant.  For species such as dock, they just fall to the ground.  The tiny amounts of seed that do travel any distance end up being a tiny drop in the ocean of weed seed already present in agricultural land.  The idea of ‘clean land’ is a myth.  Docks are not noxious.  Horses don't eat them but cattle and sheep do, and numerous scientific studies have shown they are an average to middling stock feed.  There is no loss of pasture production up to 10% dock ground cover, i.e., 10% docks = 10% more feed for free. 

With the EU wanting to slash herbicide and other biocide use, the DAFF really needs to be coming to the aid of farmers not haranguing them with nonsense legislation.  Ireland desperately needs decent IWM research capability to work out long term, sustainable strategies for managing weeds based on their biology and ecology, instead of relying on an ever-dwindling reserve of herbicides.  Take wild oat for example, organic farmers have successfully eliminated wild oat from their farms by the very simple measure of cutting and removing the seeds from the field, or deheading the plants when they are in full flower but before viable seeds are set.  Wild oat seed has a maximum viability of five years, with most dying after three.  It is a true ‘follower of man’ and can only exist within cereal fields, unlike ragwort for example that has naturalised.  If no seed is allow to return to the soil, brought in planting seed is clean then within five years, the farm will be free of wild oat and any accidental introductions are easily spot rouged out.  With such simple pieces of knowledge, farmers within a few years can eliminate wild oat from their farm and therefore the need to spray for it.  Unfortunately, farmers have limited means to produce such knowledge for themselves.  It requires good but basic agricultural science, something that is increasingly unfashionably and lacking globally, as the editor recently pointed out.  It is also not the kind of information business can make money from unlike patentable herbicides.  It is therefore, only governments and farmer levies that can pick up the tab for such research as no corporations will. 

Attempts by some landowners to control these weeds by spraying systemic herbicides over field margins and roadsides killing all plants is counterproductive.  Bare ground encourages weed seeds in the soil to germinate and for those few seeds that do disperse further, ideal conditions to grow and produce more seeds.  In non-crop areas, plants like docks and ragwort do little harm and can be left alone, along with the other plants growing there.  Spraying with herbicides simply creates an ugly yellowing mess of dying vegetation, results in a vicious cycle of continually spraying to control emerging weeds, resulting in more and more herbicide use with all the associated downsides.  If the Minister wanted to ban something that would have a positive effect it is the use of herbicides on such non-crop areas as roadsides and field margins. 

In short, there is no need for the government to lord over farmers telling them to destroy a handful of visually obvious weeds, and a dire need for the government to support farmers by funding research to allow farmers to cut their biocide use by developing biological and ecological alternatives. 

The case of common barberry is somewhat different, as the case for its control is due to it acting as the host to the sexual stage of wheat stem rust, i.e., the plant itself is not a direct problem.  Without barberry acting as an inoculum source the amount of rust on wheat is drastically diminished.  Eliminating barberry, as happened in the wheat growing areas of the United States in the 1920s, is an effective way of managing the disease as it breaks the fungus’ lifecycle.  Even more critically without a sexual stage, it is very difficult for the rust to evolve and therefore develop resistance to fungicides.  

However, just ordering landowners to destroy the plant without having a comprehensive management plan based on the epidemiology of the disease and the biology of the plant is only half addressing the issue, the government is reneging on its part of the deal.  The rust is only a problem for wheat growers so there is no need to ban what is a rather useful plant from areas where there are no wheat crops.  However, without a good understanding of the biology of the rust in Ireland, determining all the related species and cultivars that can host the disease in addition to barberry such informed decisions cannot be made.  In addition, as the Americans found out, many people can’t tell a barberry from Burberry.  It’s all well a farmer ensuring his farm is free of the plant but if the owners of the houses in the subdivision next door have no idea the nice bush in their garden could destroy the farmers wheat, little is gained.  The Americans spent a fortune sending out government workers to destroy 18 million bushes due to the lack of public understanding. 

Finally, this is not a call for abandoning the need to control invasive species, such as rhododendron.  Such species have the ability to invade and dominate natural ecosystems (non-farmland), even eliminate all other plant species and the animals that depend on them.  Control of such plants is essential. 

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Copyright 2008 Charles N. Merfield.