Gerald J. Lenhard, Louisiana State University, Bugwood.org
Common groundsel is a common annual weed that can be found in winter and summer. It's also considered a biennial in coastal areas. It has a single upright stem that grows up to 18 inches tall and features yellow flowers that bloom almost all year long. It prefers cooler, moist soils and can produce as many as three or four generations in one season.
The seeds can spread easily and create new growth throughout the landscape. Applying pre-emergent herbicides with at least three month's worth of residual control can help to prevent a widespread infestation. Herbicides with isoxaben are ideal at controlling groundsel weeds, so look for broadleaf products containing this ingredient for the best results.