Peter H. Dernoeden, Ph. D.
Where and When You Can Find Hairy Bittercress
March is the time when winter annuals spring into their full glory.
Some are competitive, while others are merely curiosity plants.
Hairy bittercress (Cardamine hirsuta) and common groundsel (Senecio vulgaris) are winter annual broadleaf weeds and among the first to flower during cool to cold weather in late winter and early spring.
Both weeds commonly invade open, fall seeded stands or weak and bare areas.
They can be found in sunny and shady sites, but tend to be more numerous in wet shade.
Although not invasive, their long stems and flowers give lawns, roughs, sports fields and sod fields a shaggy appearance until mowing operations commence.
Identifying Hairy Bittercress and Its Effects
Seedlings of hairy bittercress emerge mid-to-late autumn, but don’t become evident until early winter. Hairy bittercress produces heart-shaped leaves with three lobes, with the terminal lobe being largest.
During winter, clusters of tufted dark-green leaves are prominent. Stems are purplish-green and have a square-feel. Mature plants produce basal rosettes with deeply lobed leaves. Small, white flowers, with four white petals form in clusters on the end of stems.
Flowers can appear in late February during mild periods on top of 2” to 3” long stems. Normally by March, stems with numerous terminal white flowers grow to 4” to 12” or higher. Flattened pods called capsules form, with seed arranged in rows. Capsules are long (0.25 to 0.5” long), narrow and somewhat needle-shaped.
When mature, seeds are explosively propelled from capsules over a distance of 6’ or greater.
This is especially notable when mowing, at which time one can see and feel seeds flying and pinging. With the advent of warm temperatures in late spring plants senesce and die.
Where Common Groundsel is Found and Emergence Patterns
Common Groundsel emerges in the autumn, but does not become noticeable until late winter. Groundsel is most troublesome in early spring as plants grow rapidly above the canopy before the spring flush of turf growth.
Groundsel is mostly found in fall seeded stands of cool-season grasses and lawns with open and bare ground areas.
Groundsel also is common in ornamental beds and seed is dispersed outwards into weak lawn areas adjacent to beds.
Visual Appearance of Common Groundsel
Leaves are narrow, hairy, deeply lobed and irregularly toothed. Leaves resemble those of dandelion, but are much smaller.
Upright stems grow to a height of 4” to 10” or higher, are fleshy, square, and hairy. Yellow, dandelion-like flowers form in clusters in early spring at the tips of stems.
Once flowers mature (usually in mid-to-late March), grayish-white, globe-shaped plumes of seed develop. The yellow flowers and globe plumes of seed are similar to dandelion, but stems are much more elevated. Plants senesce with the advent of warmer temperatures and soon die.
Control and Treatment
Mowing removes stems and flowers and masks the shaggy appearance of these weeds. Herbicides usually are not needed.
In open and immature stands however; an application of a broadleaf herbicide may be advised to eliminate competition, thus speeding establishment. A 2 or 3 way combination of 2, 4-D, MCPP, dicamba, clopyralid (not for lawn use) or triclopyr normally is used, however, they do not work well in chilly weather. The addition of carfentrazone (i.e., Quicksilver) improves control when temperatures are chilly in early spring.
A Maryland study showed that a mix of 2,4-D, MCPP, dicamba and carfentrazone (e.g., Speedzone) was highly effective in controlling winter annuals when applied during chilly spring weather in a single application. This product however; has an objectionable odor and caution must be taken to avoid drift that can damage ornamentals.