PETERBOROUGH — Nearly 40 years ago, Bob Weathers worked all day to save one of the last American elms in the region from Dutch elm disease. On Friday, he watched a tree company work all day to chop down that tree, which had grown to 80 feet tall at nearly 200 years old.

The elm had finally succumbed to the disease after the rigorous annual treatment had fallen by the wayside. The treatment process requires drilling six-inch holes around the base of the tree, into which as many as 25 gallons of fungicide are pumped to course through the tree.

“It’s lots of work and there’s a cost,” said Weathers. “I can understand why nobody wanted to do it.”

When Weathers moved into what is now 42 High Street in 1951, the tree became his own. He soon partnered with then Harrisville-based Elm Research Institute to help rescue the tree from Dutch elm disease, which destroyed 100 million American elms in the span of a decade. Weathers said a plaque was installed on the tree identifying it as an historic elm.

However, the plaque has since “disappeared,” he said.

The tree was already better than four feet thick when Weathers assumed its care, and although his former high street home was built in 1903, he estimates the tree could be 150 to 200 years old.

Yvonne Spalthoff, assistant director of Elm Research Institute, now based in Keene, said Weathers’ estimate of the tree’s age matched up with the age formula based on trunk width. At its widest part, the High Street elm measured five feet thick, which places it near the two-century mark. If it had been properly cared for, the tree might have lived another 100 years, she said.

“Very sad,” said Weathers on Friday as branch after branch fell from the tree. “It should have been saved.”

Spalthoff said there are about 5,000 historic — or pre-Dutch elm disease — trees in the country, and only 92 known in New Hampshire. Spalthoff said ERI has since planted more than 250,000 Liberty Elms, a disease-resistant variety. A historic elm must measure more than 10 feet in circumference, said Spalthoff, who encouraged people to report any such elms.

“They’re very majestic,” said Spalthoff. “At one point they lined many city streets in New England and were in front of nearly every public building.”

Forester Swift Corwin of Peterborough said he had noticed the High Street elm had begun “flagging” last year, when dead and yellowing branches began to resemble flags signaling the tree’s imminent death.

“They die really fast when that happens,” said Corwin.

Although Corwin said he had no firm knowledge of the number of American elms in town, he estimated there could be fewer than a dozen old-growth elms.

“I really have no idea,” he said. “Somebody should probably take an inventory.”