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.
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 season,
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 5 or 6 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.
An amateur gardener who loves to watch the garden grow.