Ageratina

(ageratina, sticky snakeroot found at wikimedia commons, creative commons law)

This Sticky Snakeroot is a member of the aster family. It's found in Taiwan, Australia and Mexico.  This particular flower looks like a snowball bush, it's clustered flowers and broadleaved. 

The Aster family is a large family of perennials  this family consists of different types of daisies, mums and other wildflowers that multiply every single year! This is for those of you that don't have horses, but love wildflowers.

This plant is extremely poisonous to your horses. If you have this particular

plant near your equine, you need to kill it as soon as possible. It is in the same category as white oleander.  It causes colic, neurological damage and much worse.

Sticky Snakeroot is called croftonweed, ageratina adenophora. It's on the USDA invasive watch list for the entire east and west. It's also on the  federal noxious plant watchlist.  It can take a big horse down.