- Marsh Sowthistle
- Asteraceae: Sonchus
arvensis ssp. uliginosus
- CDFA A rated
 The
Santa Barbara County Agricultural Commissioner's Office reports
that a noxious weed, marsh sowthistle, Sonchus arvensis ssp.
uliginosus, has been newly discovered in the vegetable fields
west of Lompoc. Marsh sowthistle is an aggressive, hard-to-control
weed that can reduce crop yields, increase management costs,
and depreciate land values. It can also be a host to several
economically important plant pests.
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- This is a subspecies
of the noxious weed, perennial sowthistle, Sonchus arvensis.
We are considering this subspecies noxious, as well.
Noxious weeds are specifically designated by regulation as being
detrimental to agriculture, uncommon in California, and subject
to regulatory action by the commissioner. Currently, in California,
perennial sowthistle is only known to occur in Siskiyou and Modoc
Counties, and now, Santa Barbara County.
Perennial sowthistle reproduces by seed and underground roots.
The seeds can be spread by the wind and also by sticking to fur,
feathers, and clothing. Contamination of seed crops is an especially
immediate concern as Lompoc's farmers are an important producer
and exporter of flower and bean seed, worldwide.
The Agricultural Commissioner's Office will be conducting a survey
to look for other infestations of the weed and requests that
growers report any suspect weeds growing in their fields.
Perennial sowthistle looks very similar to the more commonly
found weeds, annual sowthistle, Sonchus oleraceus, and
dandelion, Taraxacum oficinale. A key distinguishing character
is that perennial sowthistle spreads by rhizomes while all other
sowthistles (Sonchus spp.) in California are tap rooted.
Because of the .JPG) rhizomatous
growth, perennial sowthistle typically forms dense stands. Perennial
sowthistle is also larger than annual sowthistle, growing up
to 6 feet tall. We have a subspecies of perennial sowthistle,
Sonchus arvensis ssp. uliginosus, that has glabrous phyllaries
(no hairs on the flower bracts).
While it is adapted to many soil types, perennial sowthistle
thrives in loose, fine, rich, slightly alkaline to neutral soils,
where there is adequate moisture. Seedlings are typically found
in cultivated fields (both grain and row crops), waste areas,
meadows, sloughs, woods, lawns, roadsides, beaches, ditches,
and river and lake shores.
Because of its extensive roots - which can grow as deep as 7
feet - vigorous growth, copious seed production, and relative
resistance to some herbicides, perennial sowthistle is difficult
to control.
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- Tillage can reduce infestations
when root fragments are buried deeply or left on the soil surface
to dry. Till when plants are in the 6-9 leaf rosette stage. Repeated
cultivation will be necessary. Tillage though, may also risk
spreading the plant. Auxin type herbicides such as 2, 4-D, dicamba,
MCPA, and clopyralid have been effective with repeated applications
when plants are in the seedling or late rosette to early bud
stages. Glyphosate may also be applied as an effective spot treatment.
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- For more information
and to report perennial or marsh sowthistle sightings call us
at (805) 681-5600 or our Lompoc field office at (805) 737-7733.
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- For more information
on perennial sowthistle, visit:
- http://www.cdfa.ca.gov/phpps/ipc/weedinfo/sonchus-arvensis.htm
- http://www.co.stevens.wa.us/weedboard/htm_weed/ps.htm
- http://www.nwcb.wa.gov/weed_info/sowthistle.html
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