I would weed the seedlings by hand. Once they're gone, she shouldn't have any more problems since the tree is gone.

Well are they seedlings or are they root suckers? You need to find that out first.

blue heron, thanks for the advice to pull out the seedlings.

If they turn out to be root suckers, what then, to get rid of them?

Leasa

If this is a poplar tree, they are probably seedlings. I have tulip poplars in my yard and seedlings appear everywhere. I just pull them, but I hate to, because tulip poplars have such beautiful blossoms in the spring.

With continued mowing and herbicide applications root suckers should be controlled with in a year or two.

Also don't confuse your lady. As we all know tulip poplar is not a poplar. It is a member of the magnolia family.