Watford revealed as worst place for Japanese Knotweed

The invasive species has been reported 72 times within a four kilometre radius of the town centre, according to a map by plant removal specialists Environet.

Cheshunt and Waltham Cross were also named as potential hotspots with 56 sightings, while Borehamwood and Harpenden had 36 and 32.

Other Hertfordshire towns saw relatively few infestations as Hemel Hempstead and Stevenage reported just 13 and six cases.

Environet warns that its presence can drop a property’s sale value by 10 per cent, while homeowners can be handed an injunction or Community Protection Notice if it affects the surrounding area.

Founder Nic Seal has 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."

Watford was revealed as the worst place in Hertfordshire for Japanese Knotweed sightings. (Image: Environet)

Sightings of the plant in the town have jumped since last September when St Albans took the top spot with 59 known infestations while Watford had 53.

The map is based on more than 50,000 records collected over 25 years and aims to inform potential buyers and sellers on the risk their property will be affected by an infestation.

The non-native plant is known to grow very quickly and can damage buildings as it spreads underground.

Japanese knotweed usually emerges in the spring. (Image: Environet)

Knotweed begins to appear in April and May, as red bamboo-like shoots resembling asparagus appear and grow over the surrounding plants and suppress their growth.

In summer, groups of white flowers appear and it can also be identified by its distinctive shield shaped leaves which have an alternating pattern.

The plant dies down in winter and goes into hibernation as its yellowy orange leaves turn brown.

It is identifiable by its bamboo-like stems and shield-shaped leaves in an alternating pattern. (Image: Environet)

Mr Seal added: "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."