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Weevils help in battle against water weed

The Canal & River Trust is set to release thousands of weed munching weevils into the River Weaver and the Shropshire Union Canal as it steps up its efforts to tackle invasive plant species.

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We’ve introduced weevils on a number of canals over the course of the last few years and have seen some encouraging results.
Chris John, ecologist

The 2mm-long weevils will be released into the river to eat the invasive North American water fern (Azolla filiculoides). The weed can be particularly problematic to the canal network due to its voracious growth which, if left unchecked, can cover the surface of a waterway with a thick weedy mat. This reduces light and oxygen levels in the water, killing fish and other wildlife.

The weevils are an effective natural means of tackling the problem of water fern. They are at their most active at this time of year and breed quickly so they can very rapidly munch their way through a very large mass of the water fern. The weevils are known to feed exclusively on azolla and don't cause damage to other native species.

Prevent the weed from spreading

Canal & River Trust, ecologist Chris John said: “Water fern was first introduced to the UK by the Victorians as an ornamental plant for ponds. As the weather gets warmer it's likely that we'll see a rapid acceleration in the growth of the weed so now is a good time to release the weevils and prevent it from spreading along the canal.

“We've introduced weevils on a number of canals over the course of the last few years and have seen some encouraging results so we hope that by releasing some more at other locations that we'll be able to more effectively control the problem across the canal and river network”.

Members of the public are asked to help combat invasive weeds by disposing of their garden and pond plants carefully, and checking cleaning and drying any fishing equipment after use.

Last Edited: 20 July 2012

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