Himalayan Balsamis an invasive terrestrial plant species that was first introduced as an ornamental garden plant and is spread exclusively by seed
What is Himalyan Balsam?
Himalayan balsam (Impatiens glandulifera) is an invasive terrestrial plant species that was first introduced as an ornamental garden plant and is spread exclusively by seed. Since it was introduced, it has spread to most parts of Ireland. It is the tallest annual plant (completes its life cycle in one year) in Ireland growing up to 3m high. The seed pods explode when mature, scattering the small seeds up to 7 metres from the parent plant. Due to its rapid growth, it shades out most of our native species. The balsam dies back in autumn, exposing the now bare bank-sides to erosive winter flows.
This invasive species is particularly prevalent in damp areas such as along the banks of watercourses, where it often forms continuous stands. It can also establish in damp woodland.
Problems caused by Himalayan Balsam
Himalayan Balsam outcompetes our native plants for space, light and nutrients resulting in the elimination of local biodiversity. This in turn can have a detrimental effect on local tourism and amenity use.
It impedes access to riverbanks for both inspection and recreational use and, because it is an annual plant, it dies back in the winter leaving bare ground exposed to erosion. Dead material can also be contributory to flooding.
Himalayan Balsam was introduced into Ireland as an ornamental plant by the Victorians. It has flourished and spread here without the natural predators and pathogens that it is susceptible to in its native range, and when released from these constraints, it is quickly becoming one of our most aggressive invasive weeds, mainly colonising riverbanks, waste ground and wet woodlands.
Elimination of local biodiversity
Erosion to riverbanks after winter dieback
Impedes access to riverbanks for both inspection and recreational use
Quickly becoming one of our most aggressive invasive weeds
Identification of Himalayan Balsam
- Grows up to 3 metres tall.
- Large pale pink-purple trumpet flowers in June – October.
- Hanging explosive seed pods that can throw seeds over 7 metres away from the plant.
- Hexagonal fleshy hollow stems that are reddish in colour.
- Dark green lance-shaped leaves with serrated edges and pointed tips.
Himalayan Balsam Key Identification
Solution for Himalayan Balsam
Reasons why Himalayan Balsam Bashing can be successful
It is possible to eradicate Himalayan balsam (not an option with most invasive plant species) from infested river catchments because its morphology and life cycle display a number of weaknesses that are uncharacteristic of such high profile invasive species. These include the following:
- the plant has an annual life cycle, meaning that it germinates, grows, flowers, seeds and dies in the one year;
- the tall plant has a very shallow root ball (picture 3) and is easy to totally remove from the soil by pulling;
- the plant has no natural defence mechanisms, such as thorns or bristles, that would make the task of pulling more difficult or hazardous;
- the majority of the seeds germinate after one year, although some may remain viable for a second year; and
- seeds are the only propagation method available to this species.
The combination of plant attributes described above for Himalayan balsam mean that it is possible for large and well organised groups to physically remove the plants from long sections of river corridor and, over a two year period, to deplete the seed reserve within the catchment. This represents an enormous conservation advantage to the aquatic and riparian ecosystem and will preserve the river banks from the erosive effects of winter floods.
How to successfully remove Himalayan Balsam from your riverbank
The following procedure should apply:
- Balsam bashing programmes should be scheduled to take place before the plant flowers and, certainly, before any seed pods are set. The ideal time is from about mid-May to the end of June.
- On river banks, plant removal operations should commence at the farthest upstream site from which the plant was recorded and work progressively downstream.
- The teams of balsam ‘bashers’ should be alerted to any risks or hazards that may exist in the targeted area (e.g. uneven banks, steep-sided banks, animal burrows, dense nettle or bramble beds, etc.) before pulling starts.
- Each balsam ‘basher’ should be equipped with strong boots or wellies, long robust trousers or leggings (to ward off the unwelcome attention of nettles or brambles), long sleeved upper garments and long durable gloves (for the same reason).
- As the plants have a very shallow root ball, they are easily removed from the soil by gently pulling. However, in order to ensure that the plant does not break when pressure is exerted on it, it is recommended that the ‘basher’ bends and grips the stem about 1 metre above the ground. Here, the stem is relatively thick and should not break when pulled. As the plants tend to grow in dense patches, it is often possible to remove two or more plants in the one go. The minimum of pressure is normally required to remove the root in its entirety from the ground.
- Having removed the balsam plant from the ground, it should be thrown landward, away from the river, where another team will gather the plants into large piles
- The piles of Himalayan balsam plants may be left in situ beyond the bankside, if permission from the landowner is granted. They will be covered with a layer of jute or hession material in order to eliminate light. This will hasten the demise of the plant and ensure that it will not flower and set seed. (It is not uncommon for plants that have been removed fully from the soil to put all of their remaining energy into flower and seed production before they die.) The jute will rot down with the composting balsam plants. Where it is not possible to leave the plant piles in situ, they will be transported to suitable licensed composting facilities.
- The day should end with a hearty barbeque, some cold drinks and a rousing sing-song.
As the seeds of the Himalayan balsam can remain viable for two years, it will be important that all participants put the date for the next balsam bash in their diary and bring a friend along to the same site the following year.
How to treat Himalayan Balsam
Himalayan balsam is an annual plant that is propegated by seed (each plant can produce 800 seeds). These can be ejected up to 7 metres from the parent plant and can be spread far and wide in streams and rivers. Each seed has a viability of 18 months. In order to achieve total elimination from a site a three year control program should be considered with the third year being used for monitoring purposes.
It is a relatively easy plant to control when a detailed management program is put in place.
The use of herbicide is the most economical and efficient method means of control. Because infestations are usually in the vicinity of water courses great care must be taken to use only approved chemicals. Treatment by herbicide can be achieved with a weed wiper in mixed stands, or by foliar spray in dense stands. Repeat checks should be carried out each year throughout the growing season to prevent any new plants from setting seed until no further growth is found. Spraying in the second year will be necessary because not all seeds germinate in their first year. Further monitoring in year three will be required, although few plants should be present.
Where cattle and sheep have ready access to areas infested with Himalayan balsam, they will effectively control it and not permit it to flower and set seed. Most grazing animals, however, do not have access to river banks where this highly invasive weed can be at its most potent. Research in the UK (under CABI) has produced a rust fungus that is showing promising signs of causing significant disruption to the growth of Himalayan balsam in early field trials. There is encouraging evidence for the potential for biological control through research ongoing in Great Britain and Ireland.
Cut at ground level (the plant must be cut below the lowest node to stop regeneration) using a scythe, flail or strimmer before the flowering stage in June. Cutting earlier than this will promote greater seed production from plants that regrow. Cutting should be repeated annually until no more growth occurs. Himalayan Balsam will regrow more vigorously and produce seeds after cutting particularly if it is cut too early.
Although this method can be successful, it is extremely labour intensive.
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