Ohio State Weed Lab , The Ohio State University, Bugwood.org
Prickly lettuce is a winter annual and has a deep taproot, which emits a milky sap when broken. It has an upright stem with lobed leaves that have spines along the midvein, especially at the lower area. During late spring and early summer, this weed produces small, yellow flowers and can grow as high as 2 to 7 feet.
This winter weed is found in the wild and in planting nurseries and container plantings. Using a pre-emergent herbicide before it pops up from the soil is the best practice. Herbicides with isoxaben are the best choice for preventing this weed from germinating and spreading. Pulling the weeds by hand is also a good method to remove them from the property.