Here’s what happened: Four years ago there were two teasel plants in a field next to a house about a mile from my home. Three years ago there were four plants. Two years ago there were seven. At that time, I became aware of the possibility of the plant becoming invasive, and I very tactfully informed the property owner of the existence of the plants and provided information about how to get rid of them. Unfortunately my warning and advice were ignored and last year there was an explosion of teasel for two miles in each direction from these two plants. Here is an example of where one homeowner could have made a positive difference, but because of laziness or indifference has launched a major invasive plant problem. And I have no illusions that the invasion will stop at two miles.
Teasel is an invasive plant of major concern in Wisconsin. It is a (get ready for a big science word) monocarpic perennial which means it flowers once and then dies. But before dying, each plant can produce 2,000 seeds, 30% to 80% of which germinate. The seeds typically do not disperse far from the parent plant, but mowing equipment and flooding can spread them. Dried teasel is commonly used in dried flower arrangements and careless disposal of the arrangements also spreads the seeds.
There are two types of teasel, common and cut-leaved, both of which are found in Wisconsin. Both types grow best in open, sunny spots and are most commonly seen along roadsides in heavily disturbed areas.
Cut-leaved teasel’s leaves have deep lobes and are broader than those of common teasel. The first year, a ground-level rosette is formed. The rosettes have oblong, wrinkled, lettuce-like leaves with a whitish mid-rib. The next year a rigid, spiny 4 to 7 foot stalk shoots up. The large flowerhead is spiny and oval-shaped. Common teasel’s flowers are purple while cut-leaved teasel has white flowers. They blossom July through September.
In recent years, teasel colonies have spread rapidly especially along highways where seeds are dispersed by mowing equipment. Teasel can form extensive (another big science word ahead) monocultures and prefers open, sunny habitats including prairies, seeps and sedge meadows where it can become a severe threat to native plants.
There are several control methods. Small infestations can be dug using a dandelion digger, since the plants form a taproot similar to that of a dandelion, although it can be much longer, up to two feet, and larger in diameter, up to an inch. The taproot can be cut through below the ground with a sharp shovel, but the area must be checked later for re-sprouts. Otherwise, cut the stalks just before they flower. They are unlikely to re-flower and will die at the end of the growing season. If the flowers have already opened, they should be cut and removed from the area, since seeds can mature on the stems after cutting. Cutting too early, before full bud stage, doesn’t do any good because the plants will send up new flowering stalks. Seeds are apparently viable for only two years, so the flower-cutting method should produce results quite quickly.
If the teasel infestation has not become too dense and there are still dried grasses or sedges present, a controlled burn in late spring can be helpful. After the burn, rosettes can easily be seen and dug up.
For thick infestations where digging, cutting or burning are not practical, the rosettes can be chemically treated in late spring or early fall when temperatures are above 50 degrees. The herbicides clopyralid and triclopyr formulated for use with water are effective.
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