Alien attack… Invasive plant species and how to deal with them. Part 2

So we are under attack, what is our response?

Well if you are enlisting then the first rule of war is to know your enemy and I will equip you (within the posts on invasives) with all you need to know to identify and tackle the  most troublesome species that threaten your garden and your environment today.

The term ‘Alien’ applies to non-native species, predominantly ones that have escaped their confines as a garden ornamental or their original indented function as a fodder grain and is now naturalising in the wild. There are many, hundreds, in tiny pockets, and many have no adverse impacts, they add nectar to the food chain and keep pollinators energized and will not spread beyond the laneway of the garden they escaped from but occasionally a non-native-species naturalises with nectar so abundant that bees neglect to visit the natives and thus risk of population extinctions exist. So your laneway of Spanish bluebells or willowherb dominates and seasonality and successive flowering species disappear from your patch, displacing pollinators and butterflies and the birds that feed upon them. Then one day you realise songbirds no longer wake you in the mornings. That’s what I mean by insidious. A slow death to diversity. A loss, slow but ultimate.

In other instances the alien plants are so competitive, spreading by root runners and simultaneous catapults of seed clusters that they overrun all the available surface ground and deny the natives a chance to reproduce, smothering out parent generation in the process and becoming the sole species in operation very hastily. It is these invasive that are the biggest threat, because there effect is quickest felt and hardest to reverse. The lane was yesterday, the hedgerow to the next county is today, tomorrow is higher taxes and local authority rates to deal with the menace, or worse spoilt water courses, closed amenity paths and ‘postcards from Ireland’ with a quaint cottage and a giant Chilean rhubarb or expanse of crocosmia where a hay field or birch grove should be. The shocking thing is that those postcards exist already. Our heritage beauty spots are daubed over with fuchsia, gunnera, crocosmia and rhododendrons. We are losing our botanical and ecological wealth.  

You will be familiar with rhododendrons. If you don’t have one in your garden already then you would have admired one in a local park or in the grounds of the last golf course, spa or hotel that you visited. These profuse flowering evergreen shrubs where introduced to Ireland in the 18th century, to do the very job that they are doing today, to be an attractive garden and landscape specimen. There are many beautiful varieties in many wonderful colours of flower but one, an attractive purple flowering variety, called Rhododendron ponticum turned out to be a fatal attraction.  It is the variety which annually and globally causes fatalities and near death experiences via what is known as mad honey syndrome; the toxic nectar it offers leads to poisoning of local honey supplies. It was this mad honey that halted Xenophon and his Greek army in their tracks and later destroyed Pompey and his roman troops when they encountered it. It is this honey that was man’s early biological warfare. It has that potential today, to ruin a honey harvest, to intoxicate bees, and to poison animals as its browsed foliage is rich also in grayanotoxin. The recognizable flowers have a small calyx with 5 blunt teeth and a lilac coloured bell-shaped corolla often with a pinkish or deeper purplish tinge. The throats of these flowers hold green-yellow spots.

In its war, this enemy secretes allelopathic toxins to salt the earth as it where and thus blight the regeneration of native plants. It forms a strong defense by growing as impenetrable thickets which cast so deep a shade that germinating light cannot get to beleaguered natives. Its establishment here was quick, having been extensively planted as game covert and demesne ornamental but its ability to regenerated rapidly after cutting, fire  and even herbicide application is matched by the enormity of wind dispersed seed that it produces annually, as much as 3-7000 per individual inflorescence. Talk about the invading hordes.  It also suckers and can root from uncleared cut branches or broken branches touching the ground. Now here is the b-movie poster: “it will not die!!!”

Ponticum leaves are long and oval, dark green above and paler beneath, approximately 10-20cm long and 2-6cm wide with a leathery or waxy texture that allows herbicide to run off and potentially enter water courses. So manual cutting and stem injecting is the current method of checking. I say ‘checking’ as that seems to be as far as it gets, eradication may take a few human generations per plant population. Unfortunately Rhododendron also acts as a host for Phythopthora ramorum a serious plant disease also known as Sudden Oak Death and of all place to impact in Ireland it struck first in Derry city, the city named after the Irish word for oak. While in County Kerry, both native Arbutus and oak woods are collapsing under the forceful colonisation tactics of Rhododendron. Elsewhere it is working its way. 

It is so costly to tackle rhodo infestations but perhaps the toxic attributes of the plant could tackle rodent infestations and the plant be harvested commercially for such, the proceeds helping to continue with its own eradication. Local authorities and enterprise boards might take note. Meantime if you are stuck with a stand of rhodos that you need to rid before they block out the last blade of grass in your lawn, then the best tactic is continual hard cutting to undermine the vigour, and then if possible dig out roots. Caution on burning stumps and branches as the smoke will also contain some minute toxins. Allow to dry, shred if possible. Persistence will be needed and so might fresh soil to the eradicated site. Make sure it is fresh.

Soil is one of the major vectors of spread for invasive species. Japanese knotweed (Fallopia japonica) especially so.  Only female plants occur in Ireland so seed is not the issue, rather it the case of extensive rhizomes which can profit to excess of 3 metres depth and extend to stretches of 7 metres laterally from a parent plant. The tiniest sliver of root is viable to produce a new parent. It was first introduced into Ireland as an herbaceous perennial for ornamental value back in the middle of the nineteenth century and it would make attractive foliage foil to any exotic or cottage border with its large foliage which is broadly oval and pointed in an arrow heart manner and bearing of a pale stripe down the middle, where it not for the fact that it outcompetes so vigorously and is so resistant to digging out or herbicide applications. Its whitish flowers are held in loose and slender panicles; they arise from the leaf axils and are a magnet to bees. Easily identified by its hollow square stems and pink new growth flushes.

Since its arrival it has escaped from gardens and parks to establish monocultures along roadsides, waste ground and river banks. In many ways it is ecologically damaging, the roots being quite penetrative and undermining to foundations and paved surfaces but it is river bank colonization that displaces indigenous root systems that prevent soil erosion, that causes most concern. A native of Japan, it is an edible delicacy there and this fact may provide a clue to checking its spread or at least making it a functional addition to our fauna. Road side harvesting is ill advised due to exhaust fumes and riverbank populations may have been chemically treated but if it rampages through your borders, why not try it steamed with some butter. Why not eat it to extinction or better still imbibe it away.

The wonder drug or uber-nutrient of recent years is Resveratrol. That miracle ingredient found in red wine, red grapes, cranberries and blueberries. That natural gift that lengthens life, fights cancer, and stimulates the SIRT1 gene. That is the gene responsible for reducing fat stores during lower calorie diets and also the key gene being studied to slow down the aging process.  Well guess what. Knotweed has it in abundance.  In China, Korea and Japan a beverage called Itadori Tea (the foliage of knotweed) is a traditional remedy for heart disease and stroke. Mildly laxative but detoxing. Again, is there a potential industry in the control of this invasive plant?

The counter attack may be more fruitful than we currently imagine.

About The Holistic Gardener

author of wellness books, columnist, keynote speaker.
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