julianna, there might be other kinds of nematodes, but my victims' roots don't rot...when I pull up the affected plant, the roots have large nodules on them. They are so misshapen that water and nutrients can't get up the plant to the leaves which results in wilt.

Here is a link that might be useful: roots pix

I think the little worms you see might be maggots. They move in after the root is rotted for some other reason- bacteria or something.
Renee

I'm having a similar problem with my Snowcaps. Large sections of them just suddenly wilt, then turn brown. I have no idea what the problem is, although I have had black-eyed susans do the same thing before.

Totally Confused

I brought-my potted Shasta daisy inside. Just found a holey leaf and green tiny worm. What is the solution