VEGETATION MANAGEMENT GUIDELINE
|Although usually called a biennial, teasel is better described as a monocarpic perennial. The plant grows as a basal rosette for a minimum of one year (this rosette period frequently is longer) then sends up a tall flowering stalk and dies after flowering. The period of time in the rosette stage apparently varies depending on the amount of time needed to acquire enough resources for flowering to occur.
During the rosette stage leaves vary from somewhat ovoid in young plants to large and oblong leaves that are quite hairy in older rosettes. During the rosette phase teasel develops a large tap root. The tap root may be over 2 feet (0.6 meter) in length and 1 inch (2.5 cm) in diameter at the crown.
Cut-leaved teasel blooms from July through September, and common teasel blooms from June through October. Flowering plants have large, oblong, opposite, sessile leaves that form cups (the cups may hold water) and are prickly, especially on the lower midrib. Stems also are prickly. Teasel's unique inflorescence makes the plant readily identifiable when blooming. Flowers are small and packed into dense oval-shaped heads. The heads (inflorescences) are subtended by upcurved bracts and are located terminally on the flowering stems. Cut-leaved teasel usually has white flowers, while common teasel usually has purple flowers. Flowering stems may reach 6-7 feet (1.8-2.1 meters) in height.
Cut-leaved and common teasel should be accurately identified before attempting any control measures. If identification of the species is in doubt, the plant's identity should be confirmed by a knowledgeable individual and/or by consulting appropriate books.
Teasel is endemic to Europe. It was introduced to North America possibly as early as the 1700's. Another species, Dipsacus fullonum, was introduced for use in raising the nap of cloth. Possibly, cut-leaved and common teasel were introduced with D. fullonum or introduced accidentally with other plant material from Europe. Teasel has spread rapidly in the last 20-30 years. This rapid range expansion probably was aided by construction of the interstate highway system. Teasel has colonized many areas along interstates. Common teasel sometimes is used as a horticultural plant, which has aided in expansion of its North American range. In particular, the use of teasel in flower arrangements has aided its dispersal, especially to cemeteries. Teasel ocurs widely in northern and central Illinois.
Teasel grows in open sunny habitats, ranging from wet to dry conditions. Optimal conditions seem to be mesic habitats. Teasel sometimes occurs in high quality prairies, savannas, seeps, and sedge meadows, though roadsides, dumps, and heavily disturbed areas are the most common habitats of teasel.
A single teasel plant can produce over 2,000 seeds. Depending on conditions, up to 30-80% of the seeds will germinate, so each plant can produce many offspring. Seeds also can remain viable for at least 2 years. Seeds typically don't disperse far; most seedlings will be located around the parent plant. Parent plants often provide an optimal nursery site for new teasel plants after the adult dies. Dead adult plants leave a relatively large area of bare ground, formerly occupied by their own basal leaves, that new plants readily occupy. Seeds may 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 capable of producing viable seed.
Effects Upon Natural Areas
Teasel is an aggressive exotic species that has the capacity to take over prairies and savannas if it is allowed to become established. Lack of natural enemies allows teasel to proliferate. If left unchecked, teasel quickly can form large monocultures excluding all native vegetation. Cut-leaved teasel is more aggressive than common teasel and has severely threatened several northern and central Illinois natural areas.
RECOMMENDED PRACTICES IN HIGH-QUALITY NATURAL AREAS, BUFFER, AND SEVERELY DISTURBED SITES
Cutting, removal, burning and herbicides offer the best solutions for control. Research is ongoing into these control methods.
Initial effort in areas of heavy infestation
In small natural areas, rosettes can be dug up using a dandelion digger. As much of the root as possible must be removed to prevent resprouting, just as with dandelions. As an alternative, flowering stalks of flowering plants can be cut once flowering has initiated. The plant should not re-flower but die at the end of the growing season. Cut flowering stalks should be removed from the natural area, because seeds still can mature on the stem even after cutting. Cutting the flowering stalk before flowering should be avoided because the plant will usually send up new flowering stalk(s). Cutting flowering stems may need to be repeated for several years to control teasel. Teasel in nearby areas should also be eliminated to prevent introduction of new seed.
Foliar application of glyphosate or 2,4-D amine herbicide is recommended where cutting (and removal) or digging-up is not feasible. Glyphosate is available under the trade name Roundup; 2,4-D amine is available under a number of trade names.
Glyphosate is non-selective, so care should be taken not to let it come in contact with nontarget species. Although glyphosate is most effective during the summer when the plant is actively growing, it is also effective in late fall or early spring. Teasel rosettes remain green and active after most prairie plants have died back in the fall, and green up and start growing in the spring before many prairie plants do. Application at these times will result in less potential harm to non-target species. Roundup should not be used to control teasel in natural areas during the active growing season of most native plants. This will result in unnecessary injury to native species.
Roundup should be applied carefully by hand sprayer to individual teasel rosettes at a 1 1/2% solution (2 oz. Roundup/gallon of clean water) during late fall or early spring. Application should be made on a spray-to-wet basis. Spray coverage should be uniform and complete. Do not spray so heavily that herbicide drips off the target species.
Application of 2,4-D amine is selective to broadleaf plants; it will not harm most grasses. The herbicide 2,4-D amine should be applied in early spring when the rosettes are young. 2,4-D amine should be applied by hand sprayer at the recommended application rate on the label for spot-spraying weeds. Application should be uniform with the entire leaf being wet. Do not spray so heavily that herbicide drips off the target species. The amine formulation of 2,4-D should be used rather than the ester formulation to reduce vapor drift.
Either herbicide should be applied while backing away from the treated area to avoid contacting the wet herbicide. By law, herbicides only may be applied as per label instructions and by licensed herbicide applicators or operators when working on public properties.
Using Roundup or 2,4-D amine on the rosettes may have to be followed with cutting of any flowering stalks that survive spraying.
Initial effort in areas of light infestation
Late spring burns may be useful for controlling teasel before it becomes dense. Once an area is densely covered with teasel rosettes, fire does not carry well through the teasel-infested area. Prescribed burns probably work best in conjunction with other methods indicated above.
In addition, teasel plants can be dug up or flowering stems can be cut and removed as described above.
The area should be monitored periodically for teasel invasion. New plants should either be dug up or flowering stems should be cut and removed as described above. Periodic fall or late spring prescribed burns should help control teasel.
FAILED OR INEFFECTIVE PRACTICES
No biological controls are known that are feasible in natural areas. Cutting flowering stems without subsequently removing the cut flower heads from the area leaves viable seed on the site. Cut flower heads can contain viable seed and the seeds must be removed from the site.
Solecki, M. K. 1989. The viability of cut-leaved teasel (Dipsacus laciniatus L.) seed harvested from flowering stems: management implications. Natural Areas Journal 9:102-105.
United States Department of Agriculture, Agricultural Research Service. 1970. Selected Weeds of the United States. Agricutural Handbook No. 366. U.S. Government Printing Office, Washington D.C.
Werner, P. A. 1975. The biology of Canadian weeds. 12. Dipsacus sylvestris Huds. Canadian Journal of Plant Science 55:783-794. (This is a good source on the life history of Dipsacus.)
Packard, Steve. 1989. The Nature Conservancy, Chicago, Illinois.
Solecki, Mary Kay. 1988. Illinois Nature Preserves Commission, Sidney, Illinois.
Written for the Illinois Nature Preserves Commission by:
Illinois Department of Conservation
Division of Natural Heritage
100 First National Bank Plaza, Suite 205
Chicago Heights, Illinois 60411