Oldham has been named among the top 10 Japanese knotweed hotspots in Greater Manchester.
According to data compiled by Environet, Oldham recorded 98 verified sightings of the invasive plant in 2026 using its Exposed heatmap, which allows users to track and report Japanese knotweed sightings across the UK.
The rankings suggest real concern for homeowners, as the presence of the plant can reduce property values and complicate sales.
Emily Grant, director of Environet, said: "Japanese knotweed is now firmly established right across the country, which means homeowners everywhere should know what to look for.
"My advice to anyone living, or buying a home in, a Japanese knotweed hotspot is to check your garden regularly during the growing season.
"At this time of year, an established knotweed plant can be identified quite easily by its hard bamboo-like canes and distinctive bright green shield-shaped leaves which grow in a zig-zag pattern along the stem.
"The earlier it’s spotted, the easier and cheaper it is to deal with.
"Acting quickly with professional advice will prevent it spreading further and help protect both your property and its value."
Japanese knotweed grows from a crown in the ground and produces tall, upright canes up to three metres high.
The leaves are large, shield-shaped, and arranged alternately along the stem.
In late summer, it produces cone-shaped clusters of creamy-white flowers.
Bolton tops the Greater Manchester list with 1,677 sightings, followed by Bury with 481.
Oldham is tenth on the list.
Nationally, Greater Manchester is the fourth worst-affected county in England, recording 3,688 sightings.
Japanese knotweed was introduced to Britain as an ornamental garden plant in the Victorian era and has since spread through the movement of contaminated soil, waterways and more than 150 years of industrial activity, construction and infrastructure works.
Although it does not reproduce by seed in the UK since all the plants are female, the plant’s root system can extend up to seven metres laterally beneath the ground, and once established, even tiny fragments of rhizome can regenerate into new plants.
The economic impact is considerable.
Environet estimates that property values drop by around five per cent, or about £13,500 per affected home.
After the fungus that causes ash dieback, Japanese knotweed is the UK’s second most costly invasive non-native species, causing an estimated £246.5 million in annual economic damage.
Anyone concerned about potential knotweed on their property can email photos to expert@environetuk.com for free identification.
If confirmed as knotweed, a professional survey can assess the risk of structural damage and recommend treatment options.
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