Only one great American Elm (Ulmus americana) remains in our small town. There are several other smaller ones but only this reminder of their former magnificence. I am still seeing more large Elms in the countryside where growing conditions are better.
I'm grateful to report once again this great Elm is leafing out!
Still Learning To See 
Lignasan BLP (carbendazim phosphate), introduced in the 1970s, was the first fungicide used to control Dutch elm disease. This had to be injected into the base of the tree using specialized equipment, and was never especially effective. It is still sold under the name “Elm Fungicide”. Arbotect (thiabendazole hypophosphite) became available some years later, and it has been proven effective. Arbotect must be injected every two to three years to provide ongoing control; the disease generally cannot be eradicated once a tree is infected. There is a process called tracing that was invented by Rainbow Treecare in Minneapolis. It has proven to be effective at saving infected elms as long as the Dutch elm disease fungus has not grown into the roots.
Have you tried any treatments on the last Elm tree? There seems to be a method for saving them which looks sucessful.
D
We’ve never had it in the budget to treat trees. It is also an pretty endless ride. We’ve planted several trees from resistant stock but they soon died. I think the future is in crossbreeding from selected resistant stock but it will take a 100+ years to get back trees like this one! One of our goals is to have a robust urban landscape that includes a diverse selection of trees to reduce the vulnerability of a reliance on monocultures like we did, historically, with Elm.