Field pennycress, more commonly known as stinkweed, is present in every state of the union except Hawaii. This weed is sparsely distributed throughout the country, but is concentrated in the Northwest. Stink weed can produce up to 7,000 seeds per plant. For this reason, it is best to kill stinkweed in a lawn before it can produce a seed head. Although keeping a thick, healthy lawn will help prevent stinkweed from becoming established, once it has become established in your lawn, a post-emergent herbicide will help you to remove stink weed from your lawn.
Mow your grass regularly. Mowing will help reduce competition for light and space, although it will not reduce competition for water and nutrients.
Select a post-emergent systemic herbicide containing glysophate. Post-emergent herbicides are formulated to kill a weed after it sprouts. Systemic herbicides pull poison down to the roots of a plant and kill the plant.
Drape a drop cloth around the stinkweed to protect the surrounding grass from overspray. If the herbicide touches the grass, it will also kill it.
Spray the systemic herbicide on the plant when field pennycress is young and actively growing. The best time to treat stinkweed is when it grows from a basal rosette with an erect, flowering stem.