Description: Teasel is a biennial,
reproducing from seeds. The first year it forms a rosette.
The second year an erect, stiff, branched stem grows to a
height of 3-9 feet. The leaves are opposite, and the upper
pairs are fused by the bases into a cup. The leaves are oblong-lanceolate
and irregularly toothed, and prickly along the edges. The
pale lavender flowers are in conical heads surrounded by long,
ascending bracts exceeding the head. Teasel flowers in July
and August. The cone shaped head makes identification of this
rapidly spreading weed fairly simple.
Distribution: Teasel was introduced into America as
a horticultural plant and for flower arrangements. Teasel
is often found around cemeteries where the dried seed heads
were used for decoration. Teasel is now found in the southern
½ of Iowa. Johnson County has several populations of
this weed, which appears to be spreading from the lack of
proper control. Teasel grows in open, sunny habitats, ranging
from wet to dry conditions. Teasel sometimes occurs in prairies
and savanna’s, but occurs most frequently on pastures,
roadsides, dumps, waste areas, and near cemeteries.
What’s The Problem?: Teasel produces abundant
seed and spreads easily and quickly. This large plant crowds
and shades out more desirable native plants. Teasel can also
be difficult to control when infestation levels are reached,
as large seed banks can stay dormant in the soil for many
years. Chapter 317, section 25 of the Code of Iowa states,
"A person shall not sell, offer for sale, or distribute
teasel (Dipsacus) biennial, ...or the seeds of them in any
form in this state. Any person violating the provisions of
this section is subject to a fine not exceeding one hundred
dollars." Greenhouses, flower shops, etc., may not sell
teasel in arrangements. This is to prevent the spread of this
invasive and noxious weed.
Management Methods: Cutting of plants, prescribed
burning, and careful use of herbicides offer the best methods
for control. A single seed head can produce 2000 seeds, so
teasel can build up a large seed bank quickly. In small infestations,
digging up the rosettes can prevent seed spread. Plants which
have flowered may be cut, but the seed head must be removed,
as these can still produce viable seed. Cutting of teasel
must be carried out over several years to achieve control.
In large infestations, foliar applications of broadleaf herbicides
can provide adequate control. Satisfactory control of teasel
can be achieved by treating rosettes in the spring with herbicides.
Be sure to read and fully understand chemical labels before
usage. Another control method that can be valuable is late
spring controlled burns. This method can be used in areas
where the rosettes are not too dense to carry a fire. Use
of all of these methods in conjunction will provide the best
control. As in any weed management program, control is accomplished
more easily if implemented before infestation.
Photo courtesy of K.R. Robertson, Illinois Natural History Survey
Above photos courtesy of Iowa Noxious Weeds published by Iowa Department of Agriculture & Land Stewardship
Photo courtesy of K.R. Robertson, Illinois Natural History Survey