Japanese Knotweed - Fall from Grace

Transcription

1 Japanese Knotweed - Fall from Grace Japanese knotweed (Fallopia japonica var. japonica), is one of a number of knotweed species, introduced into Europe in the mid 19th century (1841) by Philipp Franz Balthasar von Siebold, a German botanist and physician living in The Netherlands. In 1850 he sent a specimen of Japanese knotweed to Kew Gardens in London. Kew offered the plant for sale to local commercial nurseries, and by 1854, knotweed had travelled as far as the Royal Botanical Gardens in Edinburgh. Since first escaping from cultivation in Maesteg, Wales in 1886, Japanese knotweed now has a well-established range across the UK. It is found in over 70% of the UK hectads 10km 10km grid-squares that are used to see how widely distributed plans and animals are. It is worth noting that although knotweed may be present in these hectads, it is not necessarily abundant throughout each grid. Further afield, knotweed is now established across mainland Europe, North America and the Southern Hemisphere. This global spread is astonishing; particularly, as to date, this has only occurred via plant fragments (vegetative) and not from (viable) seed. From a horticultural perspective it is clear why knotweed was so prized for planting schemes: it is easy to propagate (spread), growing rapidly from early in the growing season to 2.5m tall and it is visually striking particularly in the summer and autumn months when it produces abundant creamy-white blossoms. However, as an ecologist, plant traits such as ease of propagation and spread are precisely why knotweed has, and will continue to be, quite literally a huge problem; both for native biodiversity and increasingly, wider society. From the past to the present With the benefit of hindsight, it can be all too easy to be critical of historic events. However, this story continues to develop into the present, as successive cycles of legislation and poorlyevidenced knotweed control practice have continued to drive further spread of knotweed in to the national consciousness and print media of the UK.

2 In the UK alone, it has been estimated that Japanese knotweed control costs the UK economy c. 170 million per annum. 1 But, until now, there has never been a study of the scale needed to truly test how effective these treatments are. They are being sold to home and landowners with no unbiased research to back up their worth. However, we have recently completed the largest Japanese knotweed field trial ever conducted globally, and working with academic and industry partners, found the best way of treating the plant long term. 2 Control not kill The key to our approach was to understand the plant, in order to control it. Japanese knotweed s ease of spread and rapid growth from a deep rhizome (root) system was initially prized for planting schemes. During our research, it became apparent that because a Japanese knotweed stand contains significant underground and spreading biomass, we would need to do large field trials, to reflect real world conditions. So, we set up 58 different 15 metre 15 metre (225 square metre) field trial plots, located in south Wales (UK), and repeated each method three times in these areas. Between 2011 and 2016 we benchmarked all 19 of the active control methods and herbicides used for controlling knotweed in the UK, Europe and America. This experiment continues to be unique in terms of scale, duration, and scientific rigour and is the largest Japanese knotweed field trial ever conducted, globally. It is plain to see why this research has not been conducted before - the commercial cost has been (conservatively) estimated at 1.2 million. However, given the on-going costs of managing knotweed in the UK, the value of the experiment is self-evident. Of the treatments tested, three were found to be significantly more effective at controlling Japanese knotweed than the others. These were treatments based on the application of glyphosate alone and at the right time of year, which is when knotweed energy is being drawn from the aboveground plant into the rhizome. The three most effective treatments were found to be (in order of effectiveness) twice yearly foliar spray of glyphosate-based herbicide, stem injection of glyphosate-based herbicide, and annual foliar spray of glyphosate-based herbicide. Although stem injection was found to be 1 Williams F, Eschen R, Harris A, Djeddour D, Pratt C, Shaw R, Varia S, Lamontagne-Godwin J & Thomas S (2010). The Economic Cost of Invasive Non-Native Species on Great Britain. CABI Wallingford. 2 Jones D, Bruce G, Fowler M, Law-Cooper R, Graham I, Abel A, Street-Perrott FA & Eastwood DC (2018). Optimising Physiochemical Control of Invasive Japanese Knotweed. Biological Invasions

3 effective, it is time consuming and uses an extremely high dose of glyphosate compared to foliar spraying. Therefore, in most instances, stem injection is a secondary option to foliar spraying, perhaps in cases when weather or geographic conditions prevent spraying. Researchers also discovered that non-glyphosate-based herbicide treatments for knotweed were definitely less effective than glyphosate-based treatments. Physiochemical treatments and physical treatments, such as aboveground covering and hand-pulling of shoots, were found to be ineffective. Other key findings of the study were that management of Japanese knotweed using herbicide treatments is about correct timing, not about excessively increasing the herbicide dose, and that it is a question of control rather than eradication. Of the nineteen treatments tested, none were able to completely kill Japanese knotweed within three years, but this does not mean that the plant cannot be successfully controlled and managed. Through our research, we have defined a new patent pending approach to Japanese knotweed treatment; The 4-Stage Model TM. This model links herbicide selection and application with the seasonal surface-rhizome flows in the knotweed plant. Importantly, we are not describing eradication (which is almost impossible to achieve in short timeframes using herbicides), but rather a type of extended dormancy where the plant does not grow above ground. Moving forwards Now, we are using our research to replace out-dated guidance based on short-term experiments and anecdotal information; in short, we re discovering how best to tackle invasive plants in real-world conditions, informed by the evidence of what actually works. About Dr Dan Jones Dan is Managing Director of Advanced Invasives Limited and an Honorary Researcher in Swansea University Department of Biosciences. Dan has a particular interest in applying scientific understanding of invasive plant ecology to real world problems.

4 Images high resolution.jpeg files available upon request Figure 1: Dan Jones. Figure 2: Plot comparison before and after treatment at the Invasives Research Centre (IRC) in Taffs Well, near Cardiff.

5 Figure 3: Figure 1: Where do you start? Japanese knotweed growing along the headwaters of the River Rhymney in South Wales, crossing public and private property boundaries. Who is responsible for the control of such infestations? Figure 4: Japanese knotweed in flower, Cardiff.

6 Figure 5: Who s problem is it? A Japanese knotweed issue that can t be ignored in Cardiff. Figure 6: Aerial view of the Invasives Research Centre (IRC) in Taffs Well, near Cardiff. Google Earth 2018

7 Figure 7: Japanese knotweed growing along the banks of the River Taff, Cardiff. Google Earth 2018 Figure 8: Japanese knotweed growing along the banks of the disused Neath Canal, Briton Ferry.

8 Figure 9: Japanese knotweed in flower, Cardiff. Figure 10: Japanese knotweed in flower, Cardiff.

9 Figure 11: Japanese knotweed in flower, Cardiff.