James Symonds, Project Officer, Scottish Invasive Species Initiative
White butterbur (Petasites albus) is a rather lovely plant in many ways. Its white, Hyacinth like flowers are, along with the Snowdrop, some of the first to be seen in the new year and can brighten up those winter walks along our rivers. In summer its plate-sized leaves create an overlapping mat of terrestrial lily pads that catch the breeze and flutter to and fro in a shimmer of white and green, very striking indeed.
However, its delicate appearance belies an insidious nature.
Native to the mountainous areas of Central Europe and the Caucuses it was, along with most invasive non-native plants species, introduced to Britain as an ornamental plant. Its introduction was earlier than most of the headline grabbing exotics like Japanese knotweed, 1683 to be precise, perhaps due to its natural range being so much closer to home. It was recorded in the wild by 1843 and is now firmly established and naturalised across much of Britain, with the North East of Scotland seeing the highest concentrations of plants.
White butterbur is a rhizomatous plant, meaning the plant has a network of roots (the rhizome) underground that are interlinked and plants grow from this root system. When the leaves die back in the late summer the plant puts energy back in to the rhizome where it is stored over winter ready for its early flowering and rapid growth in the new year. This is where its insidious nature starts to become evident.
Because of the substantial energy stores in the plants rhizome it can grow rapidly as soon as conditions allow. By mid-April early May, just when our native woodland plants are really wanting to get going, it already has a dense mat of foliage covering the woodland floor. This mat completely shades the ground meaning no other plants can access the sunlight so essential for their growth. With little or no competition, the rhizome has enough energy to spread laterally potentially, or eventually, taking over entire woodlands.
As White butterbur prefers deciduous wet woodland, it is very common along the river networks of the North East of Scotland. When the rivers flood and erode their banks, fragments of this rhizome are broken off and washed down stream where they settle and create a new stand of White butterbur and so the plant spreads, eventually taking over entire woodlands along water courses to the detriment of our native flora.
Nowhere have I seen this more evident than on the River Fiddich, a sizeable tributary of the River Spey. From its confluence with the Dullan Water in Dufftown to where it meets the Spey at Craigellechie, White butterbur has become the dominant species along its course. Anywhere that is prone to flooding is a mass of White butterbur and very little else, hectares upon hectares of ecological desert.
In these areas even young trees struggle to break through the darkness of the butterburs low lying canopy. Trees younger than perhaps 20 years are hard to find raising the question of the woodlands very existence. So what can be done?
There is, in fact, very little research out there on the control of White butterbur so here at the Scottish Invasive Species Initiative we have set up some trial sites to see what works and what doesn’t, you can read more about the details of our trial and findings here.
Early indications suggest, perhaps unsurprisingly, that application of a systemic herbicide is the most effective way of treating the plant. The most effective time to spray it seems to be once the plant is in full leaf, June onwards. At this point the biomechanics of the plant shift and instead of directing energy in to growth, energy is being transferred back in to the rhizome for over wintering, this greatly improves translocation of herbicide from the leaf that is sprayed to the rhizome which is where it is needed! That being said I have treated White Butterbur effectively in late April but these were small poorly established patches.
If your daily exercise is currently taking you for a walk along a river bank keep an eye out for this pretty little invasive (below left) and its cousins, the purple flowered native Common Butterbur, Petasites hybridus (below centre) and the formidable Giant Butterbur, Petasites japonicus (below right) with its more elaborate flower spikes and creamy flowers, the leaves of this one can get to 90cm across!!
Finally – how do you think the Butterburs got their name? Answers on the back of a postcard…