BigBill said: All I can say is that I think it was unwise to plant the same tree type back into the same hole where the previous diseased tree lived. You will just pass the same disease on to a new tree. There is no way that the disease has been removed, those roots spread out far and wide.
Trees normally live longer then 40 years, unless we are talking about fruit trees or perhaps ornamental cherries, things of that nature.
I understand. However, this particular location, between the patio and garage, really does need a tree for looks and to provide afternoon/evening shade for the patio and, eventually, the back of the house. The area has really looked bare for the last two years, and the back of the house gets very hot without shade. Even having a new, tiny tree makes a big difference for the look of the area. A locally nursery guy, the son of the guy who planted our original amur maple tree in the 1970s, said the amur maple tends to have issues like ours had and be a shorter-lived tree. Even with the issues, we liked our old tree. We considered other small trees, but decided to try another amur maple. If it doesn't work, it's not the end of the world.
NMoasis said: You didn't tell us when or how you fertilized, but rapid growth from recent, possibly excessive, fertilization would have been especially susceptible to herbicide damage. If you had a severe heatwave before the tree's roots were fully established, that would also make it more susceptible to damaging external forces.
I did not add any fertilizer to the tree hole. There has been no severe heat this summer. Regarding watering, I watered every day for a week, then gradually increased the time between watering. I'm still deeply watering once a week during the very dry stretch we've been in for the last month.
Once again, I appreciate the replies. I'll just have to see how the tree grows next year.
