It may be Erigeron canadensis, horseweed.

http://healingweeds.blogspot.com/2013/09/horseweed.html

I think Carol is right about horseweed. Horrible plant.

Ugh. I fought horseweed at my old house for years. Finally got it under control. At my new place, I have a neighbor who is not into weeding much. When I walk by, if I see a big one about to pop, I sneak in and grab it. Those seedheads fly around like dandelions and spread easily! Usually pulls out easily. very satisfying!