Deploying a natural enemy for one of the UK’s most invasive weeds

Wayne Coles, CABI
Jan 2020

For 180 years Britain’s waterways have gradually become clogged and choked with what the Victorian gardeners thought in 1839 was a pretty addition to the nation’s landscape.

But Himalayan balsam (Impatiens glandulifera), also known as Touch-me-not Balsam and Policeman’s Helmet, is no longer regarded as a visual delight but rather a blight upon Britain’s riverbanks, streams, ponds, lakes, damp woodlands, roadways and railways.

Himalayan balsam was brought to the UK by the Victorians as an ornamental plant but it has since become the scourge of the nation’s waterways – Photo: CABI

In fact, the plant – whose native range is the foothills of the Indian and Pakistani Himalayas – is considered one of the UK’s most widespread invasive weed species competing with native plant species for space, light, nutrients and pollinators, thereby reducing local biodiversity.

Though it dies back in winter, Himalayan balsam is – amongst other places – causing a nuisance on the River Tweed in Scotland as part of a nationwide invasion which in 2003 the Environment Agency (EA) has estimated would cost £300 million to eradicate. The plant has since continued to invade new areas.

Nevertheless, science is trying to fight back against the Himalayan balsam ‘menace’ with a biological weapon in its arsenal – the fungal agent Puccinia komarovii var. glanduliferae– that will be released into Scotland in 2020.

Dead plant material from Himalayan balsam can also enter rivers and increase the risk of flooding.

It was back in 2006 when CABI was asked by the EA, the Department for Environment, Food and Rural Affairs (Defra) and the Scottish Government to find a reliable. effective and safe natural enemy to help control Himalayan balsam – a journey which has seen scientists adopt a ‘classic approach’ and return to the foothills of the Himalayas for a natural solution.

After sourcing a rust fungus from the Puccinia species and bringing it back to CABI’s quarantine facilities in Egham, Surrey, for further analysis and rigorous testing scientist now believe they have a tangible biological solution for the invasive weed which will be released with funding from Scottish Natural Heritage’s Biodiversity Challenge Fund in partnership with the Tweed Forum.

Kate Pollard, a Research Scientist at CABI, said, “The highly damaging fungus was identified by CABI in the foothills of the Himalayas, where it infects leaves and kills seedlings of the plant, helping to maintain population levels.

Extensive laboratory testing was undertaken under quarantine conditions to confirm that the fungus was highly host-specific, infecting only Himalayan balsam, and safe for release.

“Approval to release the rust into England and Wales was granted in 2014 and since then, the rust has been released at 47 sites across 19 counties. Field results are promising with high levels of infection, spread and overwintering recorded at a number of sites.”

The rust fungus Puccinia komarovii var. glanduliferae could go a long way to helping to solve the River Tweed’s Himalayan balsam invasion – photo: CABI

Prior to the ‘appliance of this natural solution, Himalayan balsam on the River Tweed has been tackled using a combination of hand-pulling the weed, thanks to an army of volunteers, and spraying.

The fungus has previously been released at a site along the River Tweed on the English side of the border. It is hoped that the release later this year will help step up the fight against Himalayan balsam on the waterway further as part of a concentrated longer-term solution.

Reference
Environment Agency. (2003). Guidance for the control of invasive weeds in or near fresh water. Environment Agency, London, UK

Find out more about CABI’s work to release biological controls to fight Himalayan balsam from the dedicated website.
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Did you know?

Himalayan balsam is Britain’s tallest annual plant with each plant tending to be around 1-2 metres high, although they can reach a height of 2.5 metres in some cases!

According to Section 14 of the Wildlife and Countryside Act 1981, it is an offense in England and Wales to allow Himalayan Balsam to spread into the wild. Therefore, it is highly recommended that you remove Himalayan Balsam from your grounds or garden.

It is important to make sure that when disposing of Himalayan balsam, the waste disposal site has a permit to accept and dispose of invasive species. As GOV.UK explains, you can be fined up to £5,000 or be sent to prison for 2 years if you do not properly dispose of Himalayan balsam and other non-native invasive plants.

The Good, the Bad and the Balsam

Karen Müller, Project Officer, Scottish Invasive Species Initiative
September 2019

Himalayan balsam season has drawn to a close. On our river banks, our staff and volunteers have downed tools for another season. The time has come for the last of the pink-petaled invaders still left standing to be pinging their seeds from ripe pods in an endless effort to increase their range. But with thousands of plants degrading in piles on the banks and tens of thousands of seeds prevented from ever reaching nurturing soil we are happy to call this a job well done, for now.

It’s time to reflect on the last few months – our highs and lows, ayes and nays, lessons learned and casting our eyes to the future.

Getting to grips with balsam

This year’s waves of heat and rain appear to have been particularly favourable for balsam, with many areas dazzling with shades of pink. To counter this, a continuous thwacking of weed whackers, scythes and strimmers against balsam stems, the sound of soil releasing roots and the popping of hollow stems under the weight of more balsam being added to piles has filled the air over the last few months. There has been a flurry of volunteer activity across the project area, making it possible that river banks from Tayside to Sutherland have decidedly less of a pink hue to them.

Volunteers come in all shapes and sizes and the one lovely thing about balsam is that its control is suitable for a wide range of ages – from primary school children to people living out their best life in retirement – and can be done in larger groups. It’s the perfect way to meet new people, partake in a hands-on activity with your kids or spend some relaxing time in nature while trying something new and helping the environment. Whether it is anglers, dog walkers, bird watchers pulling a few plants when they are out and about or individual people, schools or organisations that specifically join us project officers for a balsam bash – many a mickle makes a muckle in the battle against balsam.

Compared to other invasive plant control, balsam provides instant gratification when you look back on the area you are working on – nothing makes your chest swell with pride like knowing you have just built the highest balsam pile yet of the season. And let’s not stop there, optical illusions, balsam snowmen, a spot of friendly competition who can build the biggest pile or who can scale the finished pile the fastest and stand victoriously at its summit – the pile is your oyster.

Unquestionably, balsam control is not always all sweetness and light –the plant is willing to make use of many kinds of growing spaces and so we found ourselves thigh deep in ‘bogs of eternal stench’ or crawling around in gorse on more than one occasion. Did it stop us having fun? Of gorse not!

Through the good times and the tough, plenty of opportunities to whip out the Kelly kettle, freshly brewed tea and coffee (not the instant kind, mind!) and, most vital, chocolate biscuits, support us in keeping our volunteers in top motivation.

Time to reflect and perfect

So, what have we learned over the past two seasons through trial and error? For one, we have stocked our armoury well with strimmers, scythes, weed whackers and gloves since last year – something to counter anything the balsam might throw at us.

Selectively pulling balsam from amongst other vegetation seems to have the least impact on non-target species, if compared to mowing down stretches of bankside vegetation at more badly infested sites. But, if you’re working on borrowed time, you sometimes have to face the hard hitting questions. Mowing is effective in terms of time and effort and, thus, usually prevents a much larger proportion of seeds from dropping. So, do we mow in the hope that after a couple of seasons we have adequately reduced the density and can move on to pulling the balsam up? Or shall we pull regardless of the fact that much less can be achieved in the same amount of time? It is important to ponder these quandaries and often we have to make decisions on a case by case basis, depending on the existing vegetation, how dense the balsam has become and its potential to spread from there.

As it gets later in the season the balsam is really out to impress, growing up to two meters in height. At times the stems are growing horizontally along the ground before reaching its flowers towards the sky and roots start to form on higher leaf nodes, digging into the soil where the stem touches the ground. The trouble with this is the increasing likelihood of snapping the stalk during pulling, followed by the balsam stubbornly re-growing from the left over stem. A weed whacker can be really handy here to slash the stalk below the first node closest to the ground and curbing the balsam’s ambitions once and for all.

Casting our eyes on the future, there are always things to improve. For one, we still need to understand the distribution of balsam throughout our catchments better, so that we can control it strategically from the most upper extent moving down the river. We really appreciate reports of sightings to help us with that. The species is widespread and we know that long-term, sustainable solutions require landowners who actively take responsibility and more volunteers to support the effective removal of the plants annually. While many landowners, local communities, environmental groups and countless more are already getting involved we need to increase these efforts catchment wide moving forward.

Last but certainly not least, both this year and last year it is a must to acknowledge that every single one of our enthusiastic volunteers is absolutely wonderful and invaluable! You make it a joy to get to grips with balsam and you make the improbable possible. Not all heroes wear capes – some wear waders and gloves!

If this has inspired you to get involved with the Scottish Invasive Species Initiative or you’d like to find out more, visit our website www.invasivespecies.scot or email sisi@nature.scot