Himalayan Balsam
Himalayan Balsam - Impatiens glandulifera -
is an introduced plant which has escaped from gardens and is rapidly colonising river
banks and other areas of damp ground. It is
an annual plant which grows to about 2 m with purplish-pink slipper shaped flowers in June -
August. When the seed pods are mature, they explode when touched, scattering the seed. It is
likely that the seeds are further spread by water movements. Himalayan Balsam forms dense
stands which suppress the growth of grasses and native British plants leaving the banks bare of
vegetation in autumn and winter and liable to erosion. Because Himalayan Balsam regrows
annually from seed, any form of control carried out after the seed pods have formed will have no
long-term benefit.
Control
Mechanical control - The plant is easy to cut, either by hand or machine, provided there is adequate access. However,
it often grows amongst bushes and brambles and in inaccessible locations on river banks. Unless
the plant is cut below the lowest node, it will regrow and flower later in the season. Thus, a single
cut is only effective if made very close to the soil level. Regular mowing will also control this plant
even if the cutting level is above the lowest node, provided it is often enough to prevent flowers and seeds forming. Mechanical control is likely to be effective only in areas
where good access is available to ground smooth enough for close mowing and free of shrubs or
bushes.
Small infestations can be controlled by hand pulling as the plant is shallow rooted. The seedbank
lasts for approximately 18 months, so two years control should eradicate the plant if there is no further
infestation from upstream.
Chemical control - Himalayan Balsam can be controlled by spraying the foliage with glyphosate. The plants should be sprayed in the spring before flowering but late enough to ensure that germinating seedlings have grown up sufficiently to be adequately covered by the spray.
The herbicide 2,4-D amine controls many broadleaved annual weeds and may also be used to control this species. This selective herbicide will not kill grasses which help to stabilise banks and so may be preferable to glyphosate in those situations where the weed has not produced complete cover of the grasses. A long-lance sprayer may assist in the spraying of less accessible areas out of the reach of conventional knapsack sprayers.
River bank treatment of this invasive plant can be carried out with our boat mounted sprayer and qualified operators.
Biological control - Although no specific biological control agents are known to control this species, regular grazing of infested areas by cattle and sheep are likely to prevent the spread of Himalayan Balsam either by grazing on young seedlings or by trampling.
Environmental control - The only environmental control likely to suppress the invasion of banks by this weed is the maintenance of a dense grass sward. This helps to prevent the germination of seedlings. However, once established, the shading effect of Himalayan Balsam suppresses grasses, thus encouraging further seed germination.