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Date Published: January 20, 2003
Tansy ragwort is generally a biennial forming a rosette
its first year of growth. These rosettes can range
from 5-30 cm in diameter. In the second year, it produces
a tall flower stem up to one meter in height. The
erect stem is branched from about the middle of the
stalk up to the top, and the top is often 'woolly'.
If damaged or suppressed by competition, this weed
may remain in the rosette stage for several years,
becoming a short-lived perennial.
The leaves of tansy ragwort are deeply lobed into
irregular segments. The rosette and basal leaves of
the plant are stalked, while the leaves which alternate
on the stem are not. It has a short tap-root and slightly
spreading fibrous roots which are whitish in colour.
Numerous flowerheads form in flat-topped clusters
at the top of the stems. These yellow flowers occur
in late July to August. Seeds form later in autumn
and have long silky hairs attached to one end. Although
the seeds are windborne, they often fall close to
the parent plant. The seeds are viable for many years
in the soil.
* * *
Tansy ragwort is a common weed in Great Britain.
It has now spread to New Zealand and Australia, as
well as Canada. It was first found in Canada in the
early 1900's. Other names for this weed are common
ragwort, staggerwort, and stinking willie.
* * *
Life Cycle
Tansy ragwort is a biennial or short-lived perennial
spreading by windborne seeds and root buds. Seed is
a major factor in the rapid spread of ragwort which
can annually produce up to 150,000 seeds per plant.
The roots produce buds that result in many more new
plants. New plants can also start from small root
fragments. This makes ragwort difficult to eradicate,
as you must control the roots as well as above ground
growth.
* * *
Habitat
Tansy ragwort prefers to grow in light, well drained
soils, but can become established in heavier soils,
particularly those broken up by trampling or frequent
cultivation. It is most commonly found in pastures,
hay fields, waste places, along roadsides and forest
edges.
Tansy ragwort is fairly common from Colchester County
east to Cape Breton, with infrequent occurances in
the western part of Nova Scotia.
* * *
Effects
Tansy ragwort contains compounds which are very toxic
to livestock, particularly cattle and horses. It causes
a group of diseases called seneciosis. The toxins
impede the function of the animal's liver which will
eventually degenerate, resulting in the animal's death.
Many weeks or months may pass before symptoms arise
because the animal may only be consuming small amounts,
however, damage is being done. Symptoms of seneciosis
include loss of appetite and condition, paling of
the mucus membranes, and a staggering gait or walking
in circles. Cattle may develop a mania and charge
persons in the vicinity, while horses may become very
sleepy. Critical levels required are not known, but
there is no treatment for the effects of eating tansy
ragwort.
Livestock will graze on this plant if other forage
is not available. Haymaking or ensiling does not destroy
the toxic compounds.
In addition to its toxic effects, tansy ragwort can
reduce crop yields by up to 50% in heavy infestations.
* * *
Control
A close, dense pasture sward discourages establishment
of ragwort. Land should be well plowed and cultivated
before reseeding. Mowing causes ragwort to revert
to its rosette form and produce a flower stalk the
next year, making it a short-lived perennial. Regrowth
may occur from root fragments remaining after pulling
of plants
Dicamba or 2,4-D may be used to control ragwort.
For further information on using these herbicides
or for application rates, consult your weed inspector
or consult the most recent Guide to Weed Control (Publication
75).
Biological control of ragwort can provide some control
for sites that are difficult to cultivate or spray.
The cinnabar moth is widely used because its larvae
feed on the leaves, buds, and flowers. Other insects,
including the ragwort flea beetle, and a root feeding
moth have been released in Nova Scotia.
pibw96-07
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