Dutch elm disease, which wiped out 25 million UK elm trees 40 years ago, is back.
And to make matters worse, it has been spotted in Brighton, home to the only substantial collection of elm species in the country, including the national collection of elms.
Six trees riddled with the disease have been felled, while further outbreaks are being monitored.
One 82ft (25m) high elm, felled at Brighton University, is thought to have been 150 years-old.
Some of the largest English elms in the UK are on the campus.
Assistant director of estates at the university, Andy Jupp, said: “Prompt action to destroy infected trees is the only way to limit the spread of this devastating disease.”
On her website, Sussex-based Green Party MP Caroline Lucas called the outbreak “an urgent issue”.
She said: “The 17,000 elm trees in Brighton and Hove have significance beyond the city. We need action at national level to combat tree disease.
“I tabled a written question to DEFRA to query whether the new chief plant officer will have the powers and funding to ensure that there’s a national strategy in place to stop future epidemics wiping out much loved tree species.”
Chair of the council’s environment committee, Pete West, described the outbreak as “extremely worrying”.
He said: “We ask residents to contact our parks department immediately on (01273) 292929 if they have a suspect elm tree on their property.”