Himalayan Balsam (also known as Indian Balsam) Impatiens glandulifera is a member of the Balsaminaceae family and is one of my favourite wild plants.
Article written by Graham Paul.
Unfortunately it is not a native plant in the UK and it's invasive, vigorous growth habit squeezes out all of the natural indigenous vegetation growing nearby and so earns it a ‘bad press' wherever it is found. On the positive side it is a tall, very handsome plant with dark green, toothed leaves that are attached to the stem in whorls of three. The leaves are often tipped in red and in summer the plant bears masses of attractive, fragrant flowers that range in colour from dark purple through pink to white. The flowers, shaped like a wizards hat, are suspended below a stalk in perfect balance and offering a safe landing to any passing bee in search of pollen
Himalayan Balsam goes by many other names in different parts of the country; Policeman's Helmet, Bee-bums, Jumping Jacks and Poor Man's Orchid (although this name is more commonly ascribed to the plant Schizanthus). The name Bee-bums is believed to have come from frequent sightings of the rear end of bees as they get right inside the flower in order to get at the pollen, whilst ‘Jumping Jacks' is a reference to the method of seed dispersion.
This wonderful plant originated in the Himalayas' and was introduced into Britain in around 1839 by John Forbes Royle – a native of India who was educated in Scotland and took a keen interest in botany. He was working at a hospital in Saharunpur, northern India, run by the East India Company and was also curator of a local botanical garden. Like many botanists of his era, he collected specimens whilst on survey expeditions and sent many of them back to the Horticultural Society of London. Once it arrived in Britain, Himalayan Balsam became an instant favourite in the gardens of the wealthy, who were particularly keen to seek out the larger, exotic and unusual plants to impress visitors to their grand estates. In the early days it was given the Latin name Impatiens roylei after the man who introduced it to the western world.
Himalayan Balsam is a relative of ‘busy lizzie' and is the tallest annual found in the UK, reaching a height of 2.5 to 3 metres in moist fertile soils. It has spread throughout the length and breadth of the British Isles, much of Europe, America and other parts of the world. It will survive and spread in drier, less fertile soils but in these conditions growing to a lesser height and density. Like Giant Hogweed (featured in my last article) it prefers a riparian (riverside) habitat, colonising vast areas of riverbanks, canals and the borders of lakes and ponds. The rapid and vigorous growth of this plant quickly dominates any natural vegetation nearby and causes a particular problem to the stability of soil banks alongside rivers, ponds and lakes; because, as an annual, it dies back in the autumn leaving bare soil to erode and slip into the water. In shallow waters Himalayan Balsam can grow right across the river bed in a dry year, blocking or severely restricting the flow of water.
Seed carried downstream by the river or stream is a major means of the spread of this invasive species. However, unlike Giant Hogweed, the seeds are only viable for 1 to 2 years so it is easier to eradicate the problem by killing or physically removing the plant before it gets to the flowering stage. It must be dealt with along the whole stretch of river to prevent re-infestation from upstream.
The mechanism by which seeds are dispersed is a fascinating one. The seed pod formed when the flower has been pollinated is about 20-40mm in length and contains up to 16 black seeds. The green, ripe pods have four highly tensioned sides to which the seeds inside are loosely attached.
The ripe seed pod is ‘armed' and ready to uncoil explosively in response to an extremely sensitive trigger that reacts to the slightest touch from a small insect, a falling leaf or (as was the case in these pictures) a flick of my finger! The spring-loaded sides of these seed pods hurl the seeds up to 7 metres in many different directions. This explosive ‘dehiscing' of the seed pod is common to many members of the Balsam family; such as Orange Balsam Impatiens capensis, and Touch-me-not Balsam Impatiens noli-tangere.
When Himalayan Balsam was first grown in the glasshouses of the Horticultural Society of London in the 1830's the nursery staff assumed that, coming from an exotic climate, it would be tender and need special coaxing to get it to establish in our cold northern latitude. How wrong they were soon to be proved; for the first plant raised under glass produced ripe pods that expelled seed through an open vent and allowed it to grow outside in the open the following year. Indeed, Himalayan Balsam seems to grow much stronger and healthier in our climate than it does in northern India. There are no natural enemies that specifically attack this plant, even after more than 170 years as a UK resident, and the cooler temperatures, soil conditions and high rainfall seem to positively encourage it.
Despite my own enthusiasm for this amazing plant, it remains a non-native invasive species and one that is now listed in schedule 9 part 2 of the Wildlife & Countryside Act of 1981 (amended 2010) and as such it is illegal to ‘plant or otherwise cause it to grow in the wild'.
Control Measures
Himalayan Balsam is only spread by its seed which remain viable for 1 - 2 years, so it is possible to eradicate it from an area in just 3 years by preventing growth from achieving the flowering stage.
Mechanical control by uprooting the plant may be feasible where sufficient labour is available. Alternatively, plants can be cut down by severing the stem below the first leaves to prevent stimulation of axillary buds. These methods can suit the smaller or ecologically sensitive sites.
Chemical control using approved formulations of 2,4-D or glyphosate will be effective providing optimal timing is observed. Spraying too early in the season may result in the survival of late germinating plants, which would have to be re-treated before they flower. 2,4-D is preferable to glyphosate in situations where there is a risk of soil erosion, as the latter will remove all other vegetation that might be holding the soil together. In small, easy access areas glyphosate administered by stem injection is proving to be as effective as 2,4-D in controlling the weed selectively. Any spray operation in an aquatic situation can only be carried out after first seeking approval from the Environment Agency.
Biological control of Himalayan Balsam is currently being investigated by CABI (an international research organisation -originally the Commonwealth Agricultural Bureaux) in a project led by Rob Tanner, Principal Investigator. In 2008 Rob and a team of CABI scientists from Britain travelled to the northern India where, with some logistical advice from the local CABI branch, they were able make a somewhat hazardous trek to the foothills of the Himalayas, to carry out a detailed study of the insect and fungal species found to be living off and attacking Himalayan Balsam in its native range.
This study of the natural enemies of Himalayan Balsam could provide us with some valuable weapons in the fight to control the spread of this weed in the UK. So far the CABI team have discovered some potentially interesting species; fungal pathogens - including a leaf spot disease and a rust, two stem boring beetles, a lizard beetle and moth caterpillars that were found doing considerable damage to the leaves.
The research is now continuing back in the UK in a licenced quarantine facility, to determine if it is feasible to safely release any of these potential biological control agents into the wild. It will require several years of intensive research before any biological control programs for Himalayan Balsam can be put in place.
Acknowledgements:
Tanner, R.A, (2012). An ecological comparison of Impatiens glandulifera in its introduced and native range and the potential for is classical biological control. PhD Thesis, Royal Holloway University. http://www.cabi.org/