 Texas
Blueweed (Helianthus ciliaris DC)
Family: Asteraceae (Compositae)
UPDATED AUGUST 1999
Description and Variation: A member of the sunflower
family, Texas blueweed (Helianthus ciliaris) is distinctive because of its bluish
or grayish green foliage. Lance-shaped or narrow linear leaves are sessile (attached
directly to the stem, without stalks) and may be alternate or oppositely arranged on the
stem. The margins are wavy and bear short, stiff hairs. This plant is a
rhizomatous perennial usually growing 1 to 2 feet tall with roots that reach as deep as 5
feet into the soil. The composite flower heads are 1 to 1-1/2" wide with yellow
ray or marginal flowers (less than ½ inch long) and central reddish or purplish-brown
disk flowers. Each plant may have 1 to 50 seed heads, with each of those containing
100 to 150 seeds.
Economic Importance: Detrimental: Texas
blueweed is a potential pest in any cultivated field it invades. It is unpalatable
to livestock and severely reduces crop yield in some regions. Because of its
competitive nature and persistent growth it poses the threat of becoming the dominant
plant in cultivated fields it has invaded.
Habitat: Saline or alkaline soils, sand loam ditch banks,
drainage areas, dry lakes, roadsides and cultivated fields.
Geographic Distribution: Native to the American Southwest,
it is one of the very few native plants in Texas that is also considered a noxious weed
there due to its tendency to invade disturbed areas. It has become established in
Kansas, New Mexico, Arizona and California and is also known from two sites in Twin Falls
County, Idaho. In Washington, one small infestation exists in a vineyard in Yakima
County approximately 4-1/2 miles northeast of Sunnyside.
History: Texas blueweed is native to the grasslands
of the south-central and southwestern United States and northern Mexico, and was once
considered to be the worst weed pest in West Texas, causing a greater annual loss of yield
in crops than any other weed. It is thought that its introduction to California was
due to the shipment of contaminated seed oats or alfalfa seed from Texas probably during
the 1920's. In the early 1970's it appeared in a Yakima Co, Washington vineyard and
has since not been observed anywhere else in the state. It is not known how the
plant was introduced to Washington.
Growth and Development: Strongly rhizomatous perennial
that forms dense patches in disturbed areas. Flower heads appear in mid summer and mature
in late summer. The tops of the plants then die off with the first killing frosts of
fall.
Reproduction: Plants reproduce by seed and rhizomes.
Although germination tests of seeds showed low seed viability (as low as 1%), this method
of reproduction is important in long distance dispersal. The main reproductive strategy is
through the production of rhizomes. Because rhizome fragments are capable of sprouting new
plants, cultivation in some cases may actually aid its spread by distributing fragments
throughout the soil.
Response to Herbicide: Dicamba, 2,4-D, Roundup, imazapyr,
MCPA, picloram and clopyralid are all reported to control this plant, though data are
lacking in the Pacific Northwest. Follow the label instructions for site specific
information and refer to the annually updated Pacific Northwest Weed Control Handbook.
Response to Cultural Methods: In its natural environment
Texas blueweed grows as a component of native perennial grasslands without becoming the
dominant species. The establishment of perennial grasses around an infestation may help to
control this weed.
Response to Mechanical Methods: Depleting the plant's
energy reserves by persistent pulling, digging and cultivation in combination with the use
of herbicides and the establishment of perennial grasses may be the best strategy for
control. Covering small infestations to prevent exposure to sunlight may also be a
feasible method of control and/or eradication.
Biocontrol Potentials: Texas blueweed is resistant to the
sunflower beetle and the carrot beetle.
References:
Bellue, M. 1937. Blueweed, Helianthus ciliaris, DC. is
Established in Five Counties. The Bulletin, Department of Agriculture, State of
California. Vol.26, No. 2, pp247-252.
Munz, P. and Keck, D. 1968. A California Flora. University of
California Press. Berkeley, Los Angeles and London. p.1089.
Parker, K. F. 1972. An Illustrated Guide to Arizona Weeds. The
University of Arizona Press, Tucson. pp.300-301.
Roche’, C. 1991. Texas Blueweed (Helianthus ciliaris).
Pacific Northwest Extension Bulletin PNW364. WA, ID and OR.
Schoenhals, M. G and Wiese, A. F. 1988. Control of Blueweed and
Silverleaf Nightshade. Proceedings of the Southern Weed Science Society. Texas
Agricultural Experiment Station. Bushland, Texas. Vol.41.
Texas Agricultural Experiment Station: The Blueweed and its
Eradication. 1922. B. Youngblood, Director. Agricultural and Mechanical College of Texas,
College Station, Brazos County, Texas. No. 292. pp.1-18
Rationale for Listing:
Texas blueweed establishes in disturbed and cultivated areas resulting
in dense stands that displace forage for livestock and significantly lower crop yield in
some regions. Because of this weed's limited distribution in Washington state, its
ability to out-compete desirable plants and its reputation of severely reducing land
productivity, Helianthus ciliaris meets the requirements of a Class A Noxious Weed
on the Washington State Noxious Weed List.
This page was last updated 03/31/07
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