Q. I have seen large numbers of unusual, very tall plants with small white flowers growing along roads and in fields in our area. It appears as if this plant is spreading each year. What is it? Is it a problem?
A. What you are observing is teasel; probably cut-leaved or German teasel, which is becoming quite invasive in our areas and other areas of the Midwest.
There are two types of teasel. Both types are native to Europe and were introduced to America in the 1700s. The flower heads of common teasel were used for wool fleecing, or raising the nap on woolen cloth. The roots of common teasel were also reported to have various medicinal values ranging from a remedy for jaundice to a cleansing agent. The distinctive dried flower heads are also still used in flower arrangements. Cut-leaved teasel was accidentally introduced about the same time as common teasel. Early settlers used teasel as an ornamental, and toys were made from the flowering heads.
Teasel was called Venus’ lip by the Romans. The water gathered in the plant’s leaves and the cup of the flower was believed to have cosmetic and curative powers.
Both teasel types have spread rapidly in the last 20 to 30 years – especially the cut-leaved teasel. Teasel has colonized many areas along interstates, and near cemeteries (spread from flower arrangements containing teasel left at grave sites). Mowing the plant when the seed heads are mature has also helped increase its spread near highways.
Teasels are considered to be monocarpic perennials that first form a rosette – much like a biennial. Unlike a true biennia, the rosette can remain for several years. Once the plant finally produces flowers and seeds, it dies.
A single teasel plant can produce more than 2,000 seeds. Depending on conditions, 30 percent to 80 percent of the seeds will germinate. Dead adult plants leave a relatively large area of bare ground, formerly occupied by their own basal leaves, which new plants readily occupy. Seeds may also have the capacity to be water-dispersed, which may allow seeds to be dispersed over longer distances. Immature seed heads of cut-leaved teasel are also capable of producing viable seed.
If left unchecked, teasel quickly can form large monocultures excluding all native vegetation.
Mowing and burning alone have not been effective at controlling this plant. The plant has sharp prickly spines, so it is not browsed by animals.
Young plants can be pulled, and a dandelion digger can be used to remove larger plants.
Nonselective herbicides such as glyphostae (Round-Up) can be effective. Round-Up can be applied to basal rosettes through-out the growing season. Selective herbicides containing 2, 4-D amine or tricloplyr may also be used. It may take up to five or six years of repeated treatment before the seed bank is depleted. It is important to read and follow all label directions before applying herbicides.
Many plants brought to the United States by early settlers seemed harmless when introduced. But times and climates have changed, and teasels have now become very invasive in our area.