One would be forgiven for thinking that chemical warfare is a relatively recent military lowpoint, perhaps beginning with the ‘mustard’ and chlorine gas of world war one, were an astonishing 100,000 tons of chemical warfare agents were released into the atmosphere… but no, chemical warfare is perhaps just as old as war itself. Poison arrows have been uncovered from Stone Age archaeological sites around the globe. Homer’s epics point to the bronze age utilization of poisons in war. Indian epics like the Ramayana and Mahabharata also chronicle toxic weaponry as being over 8000years in existence. The Spartans utilized with deadly effect, the noxious smoke generated by burning wood coated with mixture of tar and sulphur during their periodic wars with Athens. The Romans and the Persians utilized poisoned smoke too. The conquistadors when trying to live up their name in South America where met with a blinding resistance of fires fuelled with masses of chilies, proving chemically altered smoke as a global practice in all ages and stages of cultural development or technological ability.
The invasive plant species Rhododendron ponticum plays out its own chemical warfare: There is much debate and counter assertion as to whether or not the prime displacement of native flora in rhododendron colonized regions is down to the light depriving canopy that it quickly develops, preventing native germination or if there are some serious inhibitory effects causes by allelopathic interactions between Rhododendrons and the local plant communities. There is growing evidence that rhodos inhibit the mycorrhizal development in establishing seedlings and in the encroaching roots of competing plant species and certainly the tissues of Rhododendron ponticum do contain quite significant quantities of toxic chemicals, notably phenols and diterpenes that can alter soil makeup and thus reduce its viability for native seeds and seedlings – a sort of salting of the earth tactic. Rhodos can also through their leaf litter actually acidify soils over time and further displace indigenous populations.
In terms of those Phenols and Diterpenes , one such group known as grayanotoxins are prominent in the foliage and flowers of Rhododendrons and can poison browsing native fauna and local farm livestock. Rhododendron ponticum also contains grayanotoxin in its nectar and can pollute the honey of nearby beekeepers with what is known as ‘Mad honey disease’ – triggering intestinal and cardiac complications in consumers of the honey – more poisoning.
The two most common approaches to eradication or ‘control’ method on Rhodo colonies are felling and burning or chemical injection to kill the stem and root. Exposure to smoke is a health hazard in itself but because rhodendrons naturally contains gryanotoxins which are only destroyed at temperatures above 300 degrees it’s not the best for your personal health and if you are reading a blog called the holistic gardener then I know you won’t like to be adding to the chemical warfare with toxic chemical herbicides either.
So what can we do? Well we can lobby, like and advocate for a different strategy. I have been researching, lecturing and writing about invasive species for many years now and on that journey I have advocated that we play Rhododrendron ponticum and the other invasives at their own game, but with a twist – Just as the poison arrows of the amazon tribes led to the exploration of that poison curare and brought about medical advances in anesthesia and even the development of drugs such as Prozac, perhaps Rhododendron et al may yet yield a positive use.
Some rhododendron species have been included in the medicinal ethnobotany of people inhabiting regions where they grow, mostly as anti-inflammatory and delousing agents. I will blog more about that in the counter attack category but for now I ask – Can local governments think of harvesting it out of ecosystems, producing a product and using the profit to open a second front on other invasive?
Sure they can. It just takes enough of us to remind them.