Forest and Kim Starr, Starr Environmental, Bugwood.org
This annual weed grows low to the ground and is often confused with swinecress because of its leaves and flowers. However, this weed doesn't produce any odor, unlike swinecress which smells like a skunk. The leaves are long and narrow, and this weed produces small, yellow flowers that cluster into heads. It blooms primarily from January to May and is a member of the sunflower family.
This weed has broad leaves and can take over a lawn very quickly if it's not treated early and with the right products. Apply pre-emergent herbicides with isoxaben prior to germination for optimal results. Afterward, irrigate the area with at least a half-inch of water to get the herbicide into the soil.