Control of winter bittercress
The common name for the bittercress seen in winter is hairy bittercress. It is in our Weed Gallery in the 'Broadleaf Winter Annual' section: http://extension.umd.edu/hgic/lawns/lawn-weed-identification#winterannual Please also read the short introduction to the section. If you need a postemergent herbicide, look for one that lists hairy bittercress on the label.
It is absolutely crucial to mow your lawn high for good weed control: 3-3 1/2" is good. Some people even mow as high as 4" if they have good air circulation. The shade of the grass prevents weed seed germination.
Hairy bittercress is easy to spot and easy to pull, so if you see a rosette here and there during your winter and early spring strolls, simply pull it up.