FOR THE DAILY SOUTHERNER
Most folks recognize that spring is the time for tulips and daffodils, but have you noticed that splash of purple across your turf or throughout your landscape beds? The glowing lavender flowers of henbit, along with the white flowers of hairy bittercress will soon yield seed, resulting in an entirely new crop of problems starting next fall. Henbit and hairy bittercress are two of our common winter annual weeds in the Coastal Plains of North Carolina.
Weeds can be classified according to one of four categories: summer annual, winter annual, biennial or perennial. In the interest of space, we will focus on winter annuals for this discussion. As one might guess, the weeds thriving in the cool weather of late winter and early spring are those categorized as winter annuals. Often dismissed by home gardeners, the seeds of these garden invaders germinate in late summer and early fall, but then overwinter as small dormant plants. As air and soil temperatures increase and the days lengthen, tiny green plants burst forth in growth producing abundant flowers that complete the life cycle.
As mentioned earlier, henbit (Lamium amplexicaule) often goes unnoticed until the lavender flowers begin to open. The curious flowers develop in whorls with purple petals fused into a two-lipped structure. Another classic trademark, the distinctive square stems, places this plant in the mint family. Although the plant often dies as temperatures increase in late spring and early summer, they leave behind plenty of seed waiting to germinate the following fall. At this point, the best cultural control is to hoe and remove as many of the clumps as possible before the seeds ripen. The vegetation should be collected and removed from the beds to reduce the chance of further seed development. A number of post-emergent herbicides are also available for spot treatment control, but be aware that not all products are safe to use in centipedegrass.
The other common weed of the season is hairy bittercress (Cardamine hirsute). Recognized by its low cluster of kidney-shaped leaves and small white flowers, this plant also awakes from it dormancy when temperatures increase in late winter and early spring. The delicate white flowers extending 3-9 inches above the foliage give way to small, cigar-shaped capsules loaded with seeds. Once these curious fruit mature, the plant uses an explosive technique to disperse them. For this garden invader, time is of the essence as the seed pods are maturing quickly. Gently pull these weeds and discard them into an enclosed container. There are several post-emergent herbicides that provide effective control; however, developing seed pods can sometimes release seed before the chemical takes effect. As with all weeds, the more that you can contain the weed seed produced now, the easier your job will be next fall.
The North Carolina Cooperative Extension offers a number of valuable resources for identifying your lawn and garden weeds, as well as providing management options. Check out NCSU’s Turffiles at http://www.turffiles.ncsu.edu/ or find horticultural leaflet 644, Weed Management in Annual Color Beds at http://www.ces.ncsu.edu/depts/hort/hil/hil-644.html for more information.
(Bob Filbrun is the Agriculture Extension Agent for horticulture, forestry and beekeeping for Edgecombe County. He may be contacted by calling 641-7815.)