Common sunflower [Helianthus
annuus L.][HELAN] Photographs
Texas blueweed [Helianthus
ciliaris DC.][HELCI][CDFA list: A] Photographs
Map of Distribution
SYNONYMS:common sunflower: annual sunflower, wild sunflower,
H. a. ssp. jaegeri (Heiser) Heiser, ssp. lenticularis
(Douglas) Cockerell, H. a. var. macrocarpus (D.C.) Cockerell
SEEDLINGS:common sunflower: Cotyledons oblong, 15-40 mm long,
joined at the bases, smooth. First few true leaves opposite, dull green, covered
with short bristly hairs that are rough to touch. Margins weakly round-toothed.
Subsequent leaves alternate. No description available for Texas blueweed.
PLANT:Boths species have a strong pungent
odor, especially when crushed.
to top of page
and UNDERGROUND STRUCTURES:
FLOWERS:Showy composite flower heads solitary on long peduncles. Ray
and SEEDS:Similar to those of commercial
sunflower. Pappus scales 2(4), deciduous.
(to a depth of 20 cm at least every 2 months for Texas blueweed) reduces survival.
SPECIES:Unlike common sunflower,
prairie sunflower [Helianthus petiolaris Nutt. ssp. petiolaris][HELPE],
an introduced annual, has phyllaries typically less than 4 mm wide that
are not conspicuously ciliate and truncate to wedge-shaped leaf bases.
Disturbed sites in the San Francisco Bay region and Southern California, excluding
deserts. To 450 m (1475 ft). Maximilian sunflower [Helianthus maximilianii
Schrader][HELMA] is an introduced ornamental that has occasionally escaped
cultivation. It has short rhizome-like roots. Unlike Texas blueweed,
Maximilian sunflower lacks blue-green glaucous foliage
and has alternate entire leaves 10-30 cm long, usually folded along the midribs,
and without wavy margins. In addition, disk flower corolla lobes are yellow.
Disturbed sites in southern San Joaquin Valley (Fresno Co.) To 100 m (330
back to top of page
Prevention: Texas blueweed
is an aggressive perennial sunflower that is native to the grasslands of the
south central United States. It naturally persists in low densities in native
grasslands, but thrives in cultivated or heavily disturbed areas. Its reproductive
strategy is primarily vegetative, from root buds on lateral roots. Seed studies
from Texas have shown less than 1% of the total seed produced are viable.
However, blueweed seed may have reached California in contaminated alfalfa
or oats grown in Texas. Blueweed is highly competitive in several crops and
cropping systems including cotton, wheat, and sorghum. Texas blueweed is a
class A noxious weed in California. In agricultural fields, prevent new blueweed
infestations by planting certified crop seed and cleaning equipment after
working in infested fields.
Mechanical: The root system
of Texas blueweed is composed of two distinct parts: an extensive network
of shallow lateral roots with numerous root buds, and deeply penetrating feeder
roots. New shoots arise from root buds on the laterals and form dense semi-circular
patches. Hoeing, grubbing, or hand pulling small patches may be effective,
if continually repeated for several years. Intensive cultivation repeated
throughout the growing season for at least two years has been effective in
eradicating blueweed. This requires plowing to a minimum depth of seven inches
at monthly or bimonthly intervals. Infrequent cultivation will likely spread
the weed, as rootstocks may be severed and dragged by tillage equipment. Tillage
implements should be thoroughly cleaned after working in infested areas, to
prevent spread of root pieces to new fields.
There is no information available regarding mowing as a control strategy.
Mowing plants may prevent seed production, but should not be done after seed
Grazing: Livestock may graze
young, newly emerged shoots, but tend to avoid plants as they mature. Maintaining
a healthy, competitive range may prevent blueweed from becoming established.
However, it will persist in native grasslands and may increase if overgrazing
Chemical: Certain herbicides
have provided control of blueweed in the south central United States. However,
repeated applications may be necessary, and control may vary depending upon
the year. Dicamba, 2,4-D, MCPA, and picloram have been reported to control
blueweed. Clopyralid, which is now labeled for use in California rangelands,
is very effective on common sunflowers and may also control or suppress blueweed.
Imazapyr and glyphosate may also be effective for blueweed control. Refer
to the herbicide label for rates and timings.
to top of page