THE hot humid weather may be a bit wearing for some of us but one plant, the Himalayan balsam, seems to have thrived and has grown in many areas with alarming vigour.

Himalayan balsam is the tall, sickly-smelling, pink flower that is commonly seen growing around the banks of streams and rivers and in many damp places.

The flower has a distinctive shape that has led to the plant acquiring the country name of "policemen's helmets".

Despite the abundance and widespread nature of this plant, it is only a recent arrival in this country with the first specimen being planted in a horticultural garden just over 150 years ago.

The ease with which this plant grows and the wealth of attractive, almost orchid-like, pink flowers made it a great hit with Victorian gardeners looking for that something a little bit different.

In this way the introduced plant found its way around a lot of the country.

If this were the only way that Himalayan balsam could propagate itself in the country there would not be a problem.

However, Himalayan balsam is very effective at spreading its own seeds. Once the flower has been fertilised, usually with the help of honey and bumblebees which seem to love this flower, a distinctive seedpod develops.

This pod, as most schoolchildren know, explosively scatters seed up to 12 metres away when it is ripe.

If the seed lands on reasonably fertile ground it will result in a new plant next year or, if the seed lands in water, it floats along until, either by flood or fortune, it finds itself on a peace of drier ground and will sprout here.

Each plant will have a couple of dozen pods with each pod scattering up to a dozen seeds. In this way the Himalayan balsam has spread across all of Britain, taking over any slightly damp spot it can find.

It would not be so bad if Himalayan balsam was a small unobtrusive plant but this is far from the case. Given half a chance Himalayan balsam will grow up to three metres tall in just three months. This rate of growth is unmatched by any of our native flora.

This results in our natural wild flowers being shaded out from light and hence dying off.

The Himalayan balsam is responsible for the marked decline of native British wetland flowers seen in the summer.

Worse still, even when the plant dies back in winter, it leaves its dead stems which shade out the springtime wildflowers as well.

What can be done? On the Wyre forest district nature reserves two methods are used to control this plant.

The most effective of these is the introduction of grazing as the cattle really favour these plants and, on sites where previously this was a prolific problem, it has all but been eliminated.

Unfortunately not everywhere is appropriate to graze, so in these areas the plant is actively cut back as it comes into flower. This is laborious work and not half as effective but it is all we can do to stem this balsam invasion.