I had a problem in my garden some time back. (Actually, I have continuous garden problems, enough to make me wonder why I'm doing it at all... but this was the most interesting one.) I found a rather thready orange-colored growth in the chive patch. Then it spread to the (volunteer) tomatoes and to the squash. This was a problem, since it looked like it was actually killing the tomatoes, though the chives had shown little ill effect from it.
It turns out that what I had in my garden was a plant vampire called Dodder. You can also look here for a more detailed picture. Recently it was discovered that Dodder plants actually choose their victims, and prefer real tomato plants to fake plants and vials of colored water. Fascinating!
It is apparently not subject to any known herbicides, you just have to pick it out, and remove any (parts of) plants to which it has attached itself. I have now done that arduous process, and my patch appears Dodder-free. For now.
I hope you have not found Dodder in your garden.