Common and Cut-Leaved Teasel Control
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 stage teasel develops a large tap root. The tap root may be more than 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. Cut-leaved teasel can also be distinguished from common teasel by its irregularly pinnately-lobed upper stem leaves. Upper stem leaves of common teasel have smooth margins. Flowering stems may reach 6 to 7 feet (1.8 to 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 1700s. Common teasel was introduced for use in raising the nap of cloth. Possibly, cut-leaved teasel was introduced with common teasel or introduced accidentally with other plant material from Europe. Teasel has spread rapidly in the last 20 to 30 years, spreading from Quebec and Maine to Ontario and Michigan, then south to North Carolina, Tennessee and Missouri. 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 grows in open sunny habitats, ranging from wet to dry conditions. Optimal conditions seem to be mesic habitats. In Illinois, teasel sometimes occurs in high quality prairies, savannas, seeps, and sedge meadows, though roadsides, railroads, dumps and other heavily disturbed areas are the most common habitats of teasel. Missouri locations are predominately highway rights-of-way at present, but the potential is great for eventual spread into a variety of other natural and disturbed sites.
A single teasel plant can produce more than 2,000 seeds. Depending on conditions, up to 30 to 80 percent of the seeds will germinate, so each plant can produce many offspring. Seeds also can remain viable for at least two 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. Common teasel may also have this capability.
Effects Upon Natural Areas
Teasels are aggressive exotic species that have the capacity to take over prairies and savannas if 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 natural communities of high quality
For small populations or if large, cheap labor pools (volunteers) are available, mechanical methods work quite well. Young rosettes can be dug up using a dandelion digger. Just as in digging up dandelions, as much of the teasel root needs to be dug up as possible. Once the rosettes get large, it is difficult to dig the roots up without doing damage to the natural area around the plant. Very small seedlings can be pulled up by hand when the soil is moist. Flowering plants can be cut before seed set. At the initiation of flowering, the flowering heads should be cut off and removed from the natural area. Removed immature seed heads left in place can still develop some viable seeds. Once the flowering heads have been removed, the flowering stalk should be cut off at or slightly below ground level. A machete is useful in cutting off the flowering stalks. Cutting off the flowering stalks just at flowering time will usually prevent re-sprouting from the root crown. Cutting flowering stalks prior to flowering should be avoided since the plants will re-sprout and flower again. A later inspection should be performed to catch any root crowns that do re-sprout.
Probably the most cost effective method of control is the use of foliar applied herbicides. Any of the herbicides recommended below for buffer or disturbed sites can be used, but with greater care to prevent damaging native plants. Spot treatment with backpack sprayers is probably the preferred method in high quality areas as opposed to high volume units. Triclopyr is a good choice during the growing season since it usually does not harm the monocots. Some grass species will be burned back by Triclopyr, but will usually come back. During the dormant season Glyphosate has worked in controlling teasel in some situations. Triclopyr may also work during the dormant season, but has yet to be tested.
Prescribed burning as suggested below in conjunction with herbicide treatment is probably the best strategy to insure complete coverage.
Recommended Practices on lands other than high-quality natural areas
The most cost effective control method for heavily infested sites is the use of foliar applied herbicides. Glyphosate (under trade name Roundup), 2,4-D amine (under various trade names), and Triclopyr (under trade name of Garlon 3A) have all been used successfully. Triclopyr and 2,4-D amine are dicot specific and should not harm monocots. Both herbicides should be applied during the growing season, preferably before the plant has bolted (sent up a flowering stalk). Triclopyr appears to be slightly better at controlling teasel than 2,4-D amine. Application can be made after bolting, but there is a risk of the seeds still developing, depending upon the date of application. Neither of these herbicides have been tried during the dormant season, but they may be effective. The rosettes of teasel stay green late into fall or even into winter when most other plants have died back. Application at this time would allow treatment without harming other dicots.
Glyphosate will kill any green plant. To avoid killing monocots, Glyphosate should be used sparingly during the growing season. If harming other plants in the immediate vicinity is not a problem, Glyphosate is quite effective. Glyphosate should be applied before the plant bolts. Glyphosate can also be applied after bolting, but again there is a risk of the seeds still maturing. Glyphosate can also be applied during the dormant season. The results of dormant season treatment are mixed, some individuals have reported success and others failures. The condition of the rosettes and daytime temperature are probably important factors. Rosettes in good condition on warm days are probably photosynthesizing and Glyphosate would be effective. Stressed plants and plants on very cold days may not be photosynthesizing and Glyphosate may not be effective under these conditions. More research is needed on the use of Glyphosate during the dormant season.
These herbicides can be used as a spot treatment method with a backpack sprayer. A 1.5- to 2-percent solution of Glyphosate is effective. A 2-percent solution of Triclopyr has proven successful. Triclopyr needs the addition of an agricultural non-ionic surfactant. Herbicide coverage should be thorough to wet all the leaves and stems. Use of high volume equipment (booms, etc.) may be possible in highly disturbed areas where there is little likelihood of damaging wanted vegetation. By law, herbicides may only be applied according to label directions. Prescribed burns may make detection of teasel rosettes easier. Small rosettes can be hidden in the litter, while dried grass and forb stems can make complete spray coverage with a herbicide difficult. Either fall or spring burns would open up the area for detection. Fall burns would allow detection of rosettes during the dormant season. There is some evidence that singed rosettes may not be as active during the dormant season, and not as susceptible to herbicides. Fires will not carry well through dense stands of rosettes, so singed rosettes may only be a problem around the periphery of an infestation, or with isolated plants.
Additional suggestion on control of teasel
Several years treatment may be necessary to totally eradicate teasel from a natural community. It is important to prevent all seed production so that there is no addition to the seed bank in the soil. It may take several years (even up to five or six years) of repeated treatment before the seed bank is depleted. It is useful to map locations of infestations and treatment so that they can be readily located in future years.
If treated in the early stages of infestation it is possible to cheaply and quickly control teasel. If teasel is noticed outside, but near a natural community, get control of the teasel before it gets into the natural community. As with all exotics, start control before they become a serious problem.
Failed or Ineffective Practices
Mowing is ineffective because the root crown will re-sprout and flower after being cut. Even repeated mowing is ineffective. Repeated mowing will stop some plants from flowering, but others will produce short flowering stems that may be short enough to be below the height of the mower. Plants that have been knocked over by a mower and not cut off will lie horizontally and produce short flowering stalks below the height of the mower.
Cutting off the flower stalks at flowering time and leaving the flowering heads has been shown to be ineffective. Viable seeds can still develop from the cut stems. The flowering heads should be removed.
Prescribed burning alone is ineffective. Prescribed burning may kill some of the isolated small seedlings, but is ineffective against dense seedlings or large rosettes. Many seedlings germinate around the parent plant where shade from the parent plant has created a bare soil area. Fire will not carry through these bare soil, low fuel areas. Teasel remains green late in the fall and into winter, and also greens up early in the spring. The green teasel plants in areas of large infestations stop the fire from carrying into the interior of the population.
No biological controls are known that are feasible in natural areas.