Tansy ragwort [Senecio
jacobaea L.][SENJA][CalEPPC: B][CDFA list: B] Photographs
Map of Distribution
Common groundsel [Senecio
vulgaris L.][SENVU] Photographs
Oxford ragwort [Senecio
squalidus L.][Bayer code: none][CDFA list: B] Photographs
Map of Distribution
plants with alternate, pinnately lobed leaves. Many Senecio species
contain pyrrolizidine alkaloids toxic to humans and livestock
when ingested in a single large quantity or in small amounts over time. Cattle,
horses, goats, and young animals are more susceptible to poisoning than sheep.
Introduced from Eurasia.
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SEEDLINGS:Remain as rosettes until maturity. First leaves alternate.
Subsequent leaves variable, margins toothed to deeply pinnate-lobed.
PLANT:Foliage glabrous to lightly covered
with long wavy to cottony hairs, especially along midveins and on lower leaf
surfaces and new growth. Leaves highly variable, +/- evenly spaced on stems.
Lower leaves taper into indistinct petioles. Upper leaves reduced, sessile,
+/- clasp stem.
and UNDERGROUND STRUCTURES:
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FLOWERS:Flower heads yellow, clustered at stem tips. Phyllaries
(flower head bracts) often black-tipped, in 1 equal row,
typically with a few highly reduced phyllaries at the base. Insect-pollinated.
and SEEDS:Achenes cylindric with shallow
ribs, 1.5-3 mm long, light brown, often pubescent. Pappus bristles numerous,
soft, white, about twice the achene length. Pappus +/- deciduous.
CHARACTERISTICS:Dead brown stems can persist
for several months.
HABITAT:Disturbed sites, waste places, roadsides.
PROPAGATION/PHENOLOGY:Seeds (achenes) disperse with wind, water, agricultural machinery,
and by clinging to fur, feathers, and feet of animals and shoes and clothing
SPECIES:Woodland groundsel [Senecio
sylvaticus L.][SENSI] is an introduced European annual of open, disturbed
woodland and rocky areas along the Central and North Coast. It resembles common
groundsel, but unlike common groundsel, woodland groundsel
lacks or has a few inconspicuous reduced phyllaries with green tips.
In addition, it has a few (< 8) ray flowers with corollas that barely extend
beyond the main phyllaries. Purple ragwort [Senecio elegans
L.] is an escaped ornamental annual from South Africa that grows on disturbed
sites along the Central and South Coast. It is easily distinguished from other
ragworts by its purple ray flowers.
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Prevention: Tansy ragwort
is an aggressive biennial in the Asteraceae family. Native to the Mediterannean,
it was introduced into northern California and the Pacific Northwest in the
early 1900's and is now a problem in forest clearings, pastures and disturbed
areas across the region.
Tansy ragwort is highly poisonous to cattle and horses and also toxic to goats.
The responsible compounds are pyrrolizidine alkaloids that are converted to
toxic pyrroles in the liver. Cattle are poisoned after ingesting only 2-8%
of their body weight. The toxic effects are often sublethal or only become
apparent several months after ingestion due to irreparable liver damage. Sheep
are generally not poisoned by tansy ragwort and may be used in control strategies.
Normally, cattle and horses will avoid grazing tansy ragwort due to its bitter
taste. However, in heavily infested areas, or where tansy ragwort occurs in
close association with desirable forage species, consumption is more likely
due to limited selectivity in grazing.
Seed production may exceed 150,000 seeds per plant and seed viability in the
soil can exceed three years. Tansy ragwort seed is primarily dispersed by
wind (generally less than 10 m), water, animal hair or fur, and human related
activities such as hay and straw transport. The spread of tansy ragwort can
be reduced by using certified weed free hay and preventing overgrazing.
Oxford ragwort is an annual or bienniel herb that is not currently known to
be in California. A single population was previously eradicated from the Berkeley
Botanic Garden. However, in England, this species escaped from the Oxford
Botanic Garden in the 19th century and rapidly spread across Southern England.
There is no information available concerning management practices for Oxford
ragwort. Therefore, the following information is based upon management practices
for Senecio jacobaea.
Mechanical: Mowing tansy
ragwort during the early flowering stage can reduce seed production. However,
this generally stimulates new shoot production from the crown and a second
crop of short-stemmed flowers is produced. Additionally, mowed plants may
survive as short-lived perennials into the next year and produce a greater
seed crop than unmowed plants. Repeated mowing of regrowth in the bud stage
will reduce the secondary seed crop. It is critical to clean any mowing equipment
after working in infested areas to prevent spread to new areas.
The toxic alkaloids remain in cut stems for a considerable time period following
mowing and animals should not be allowed to graze recently mowed areas. One
of the most important avenues for livestock poisoning is through ingestion
of contaminated hay. Tansy ragwort patches should be avoided during hay cutting
Hand pulling is effective on small infestations. It is important to remove
the root system to prevent regrowth from the crown and root buds of the plant.
If plants have set seed, they should be carefully removed, bagged, and burned.
Repeated tillage is an effective method for tansy ragwort control, however,
tansy ragwort is generally not a problem in areas where tillage can be used.
Regeneration of plants may occur from severed roots and crowns and tillage
equipment should be cleaned after being used in infested areas.
Biological: Tansy ragwort
is one of the best examples of effective classical biological control. There
are three insects in California that have been approved and released for tansy
ragwort control: the ragwort flea beetle (Longitarsus jacobaeae), ragwort
seed fly (Pegohylemyia seneciella), and cinnabar moth (Tyria jacobaeae). The
damage inflicted by these insects is often complementary. The flea beetle
larvae feed on the roots and crowns and the adult beetles feed on the leaves.
The seed fly larvae feed within the seed heads and the cinnabar moth larvae
feed on the leaves, buds and flowers.
Flea beetles can be collected in the fall on new rosettes. The typical method
of collection is a specialized vacuum apparatus. The adults can be transported
in cool cardboard boxes with ample rosette leaves for food to new sites for
release. A population of 250-500 insects is necessary for establishment. Establishment
of populations may take up to five years. However, once established, these
insects have provided greater than 90% tansy ragwort control in western Oregon
and Washington and northern California.
Cinnabar moth larvae are easily recognized by black and yellowish-orange bands.
They are effectively distributed by collecting several hundred larvae and
transporting them in cool, cardboard boxes to new infestations. The larvae
must be supplied with ample food during the transport process. The seed fly
is already widely distributed in infested areas. When used alone, the seed
flies are ineffective in reducing the tansy ragwort population.
Sheep may also be used for tansy ragwort control. Sheep are normally quite
tolerant to tansy ragwort and will preferentially graze it in the summer.
Continuous sheep grazing may prevent tansy ragwort from setting seed. However,
this may also extend the life of the plants an additional year. Intensive
sheep grazing in tansy ragwort infested areas has also been used as a pasture
preconditioner for cattle.
Fire: There is little information
regarding the use of fire for tansy ragwort control. Burning at the early
flowering stage may reduce seed production. However, resprouts from the crown
and seedling flushes in the following year are highly likely. In addition,
exposed soils are susceptible sites for rapid re-establishment of tansy ragwort
from wind dispersed seed.
Chemical: Tansy ragwort
is susceptible to most auxin type herbicides in the seedling stage. 2,4-D
in the LV ester or amine formulations at 1-2 lb ae/A is most effective when
applied during the rosette stage and control decreases as plants begin to
bolt. Dicamba (1 lb ae/A) is effective when applied from the rosette to bud
stage. Picloram (0.25 lb ae/A) is not commercially available in California,
but is effective up to the flowering stage. Clopyralid has given mixed results
in studies and is not recommended as a stand-alone treatment. Metsulfuron
(0.6 oz ai/A) plus a surfactant is effective on actively growing plants. Triclopyr
plus 2,4-D (0.375 lb ae/A+ 1.0 lb ae/A) can be applied to plants in the rosette
to early bud stages.
These treatments may not provide complete control and regrowth is likely to
occur. Fall applications followed by a second spring application to any regrowth
is more effective. Always consult the herbicide label for specific directions
Integrated Pest Management:
The use of the biocontrol agents is probably the most effective long-term
management strategy. However, occasional flare-ups in the population are likely,
until the biocontrol agents build up enough to provide control. Flare-ups
should be checked for the insects and supplemented if few insects are found.