Do you live in a Japanese knotweed hotspot? St Albans, Watford and Hitchin are the locations in Hertfordshire that are worst affected by the UK's most invasive plant, according to experts.

Invasive plant specialist Environet has analysed the latest data from its live online tracker to reveal this year’s Japanese knotweed hotspots. With 59 known infestations, St Albans takes the top spot in Hertfordshire, followed by Watford with 53. Hitchin has 31 known infestations and Harpenden has 29.

The Comet: Japanese knotweed is identifiable by its hard, bamboo-like canes and distinctive shield-shaped bright green leaves which grow in a zigzag pattern along the stem.Japanese knotweed is identifiable by its hard, bamboo-like canes and distinctive shield-shaped bright green leaves which grow in a zigzag pattern along the stem. (Image: Environet)

In Hertfordshire, there is a total of 423 known infestations, according to Environet, and more than 58,000 known infestations across the UK. Mature plants flower in August, becoming covered in clusters of delicate tasselled creamy-white flowers.

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Japanese knotweed usually emerges in March or April and grows rapidly to reach up to 2.5 metres in height by mid-summer.

It is identifiable by its hard, bamboo-like canes and distinctive shield-shaped bright green leaves which grow in a zigzag pattern along the stem.

It is usually spread accidentally through the movement of soil or garden waste, or via rivers and streams.

Tackling knotweed costs the UK economy nearly £250 million a year, and homeowners are one of the groups most at risk – not only from potential damage to their property, outbuildings and gardens, which can be costly to repair, but also from legal risks arising from encroachment or when properties are sold.

The Comet: Japanese knotweed usually emerges in March or April.Japanese knotweed usually emerges in March or April. (Image: Environet)

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Nic Seal, founder of Environet, said: "Vigilance is the best way to protect your property from the risks posed by Japanese knotweed.

"Make sure you know what knotweed looks like and how it differs from other common garden weeds like ivy and bindweed, so you can keep an eye out for it in your garden and neighbourhood.

"Knotweed is easily identifiable during summer, but as we head through the autumn and into winter, the above-ground growth dies back and it becomes much harder to spot. It’s also easier to conceal, so anyone viewing a property to buy should be extra careful.

"There are lots of horror stories out there but, with professional help, knotweed can be successfully treated and a property’s value can be largely restored."