NEW shoots of Himalayan balsam are now appearing on Worcestershire riverbanks and landowners are being urged to pull them up before it is too late.

Unless they are uprooted now, they will grow into tall vigorous plants that smother native species such as meadowsweet and marsh marigold.

The pink flowers that appear from July onwards look pretty, but each one will develop into an explosive fruit that bursts with a pop, firing its seed as far as five metres. Just one plant can produce 500 seeds, which may be carried downstream and grow further along the riverside.

Andy Harris, conservation officer for Worcestershire Wildlife Trust, said: "Every year volunteers help us with the battle against Himalayan balsam on a number of our nature reserves.

"With concerted efforts we are having results and it is wonderful to see the meadowsweet, angelica and marsh marigold thriving again."

The trust wants landowners and managers to tackle the plant now, before it produces seeds.

It has to be pulled up before the fruits ripen and then burnt or left to rot above ground, because the plants will soon re-establish themselves if left on the soil.

Peter Hughes, manager of the Madresfield Estate, said: "We don't have a particular problem with it on our estate, because the river bank is grazed by sheep and cattle." But he said it could have a cost to farmers, by endangering their claim to a Single Farm Payment for good stewardship of the countryside.

Summer stands of balsam up to 10ft high along parts of the River Teme prevent walkers from seeing the river, while anglers are forced to hack through the jungle to get to their fishing platforms.

The chairman of St John's Angling Society, Brian Smith, claimed it would be impossible to eradicate now. "The seeds are in the ground and lie dormant for years," he said.

NO NATURAL PREDATORS OR PESTS

l Himalayan balsam originally came from the Himalayas.

l It was introduced to Britain in the 19th Century.

l It grows where there is an accumulation of silt along a river or stream.

l It has no natural predators or pests.

l It has an unpleasant smell when it dies back after seeding.

l It is also known as Policeman's Helmet, because of the shape of the flowers.

l The plant is an annual, so its seeds must be scattered for more plants to be able to grow next year.