Henbit.

Pull & trash all you find before they set seeds.

It also known as: deadnettle, henâÂÂs bite, henbit deadnettle, henbit nettle.

Thick mulch or soil solarization can help prevent henbit establishment. Seed production can be prevented by digging, hand-pulling, hoeing, tilling, or mowing in the fall or spring. Henbit grows best in moist, fertile soil, in newly-seeded or sparse lawns, and in other open areas.

I don't think this is Henbit (Lamium amplexicaule). I think it is Lamium purpureum (Red or Purple Deadnettle).

yeah, I agree with flora_uk, this is Purple Deadnettle. Henbit looks slightly different. I've been researching weed pics myself and found almost exact matching pic of your weed on this website: http://weeds.cropsci.illinois.edu/weedid.htm