Common sunflower

Helianthus annuus L.

Common sunflower vegetative plant
Common sunflower plants in flower
Common sunflower seedlings

Images above: Upper left: Common sunflower vegetative plant (Anita Dille, Kansas State University). Upper right: Common sunflower plants in flower (Anita Dille, Kansas State University). Bottom: Common sunflower seedlings (Anita Dille, Kansas State University).

Identification

Other common names:  sunflower, wild sunflower

Family:  aster family, Asteraceae

Habit:  Tall, upright, branched summer annual herb.

Taxonomic note:  The species Helianthus annuus has been classified into a cultivated subspecies (ssp. macrocarpus), a wild subspecies (ssp. lenticularis), and a weedy subspecies (ssp. annuus) (Duke 2001).  Since weedy populations are often more genetically related to nearby wild populations than to each other, the validity of the weedy forms as a taxonomic entity is in doubt (Kane and Rieseberg 2008).

Description:  Seedling stems below the cotyledons are green to purplish.   Cotyledons are oblong, hairless, 0.5-1.5” (1.3-3.8 cm) long by 0.25-0.5” (0.6-1.3 cm) wide, and fused at the base.  The first one to three pairs of true leaves are opposite, and all subsequent leaves are alternate.  Early leaves are dull green above, light green below, toothed on edges, and coated with rough, stiff hairs on both surfaces.  Leaves are oval to lance-shaped with a tapered and rounded tip.  Mature plants are typically 2-10 ft (0.6-3 m) tall.  The stems are erect, branch occasionally towards the top, and are densely covered in coarse, spreading white hairs.  The leaves are 4-12” (10-30 cm) long, egg-shaped to triangular or heart-shaped, stalked, toothed, and conspicuously 3-veined.  Both surfaces of the leaves are covered with stiff white hairs.  Upper leaves have shorter stalks than lower leaves, and may be lance-shaped.  The root system is a taproot with branching and spreading fibrous roots.  From 1 to 12 flowerheads occur at the end of stems and branches.  The flowerheads are long-stalked, 3-15” (7.6-38 cm) wide, and consist of 20 to 40 yellow petal-like ray flowers surrounding numerous red- to purple-brown disk flowers.  The yellow ray flowers are 0.6-1.6” (1.5-4 cm) long, whereas the disk flowers are 0.2-0.3” (0.5-0.8 cm) long.   Beneath the flowerhead are 2 to 3 rows of overlapping hairy, green, tapered oval bracts.  Seeds are encased in a hard, dry fruit known as an achene.  These units (hereafter called seeds) are 0.13-1” (0.3-2.5 cm) long by 0.1-0.6” (0.25-1.5 cm) wide, oval, flattened, and are tipped with 2 to 4 bracts which detach at maturity.  The seeds are white, gray, brown or black and are often mottled or streaked.

Similar species:  Several species of Helianthus are similar to common sunflower.  Prairie sunflower (H. petiolaris Nutt.) is an annual species with smaller, 1-2” (2.5-5 cm) wide flowers, and narrower, 2-6” (5-15 cm) long by 0.5-3” (1.3-7.6 cm) wide triangular to lance-shaped leaves.  The rhizomatous perennial Texas blueweed (H. ciliaris DC.) is shorter than common sunflower, 28” (71 cm) tall and has lance-shaped, blue-green leaves.  Jerusalem artichoke (H. tuberosus L.) is a rhizomatous perennial that produces knobby, irregular tubers at the rhizome tips.  Jerusalem artichoke leaves are narrower, 1.6-4.7” (4-12 cm) wide, than common sunflower, and the flowerheads are smaller, 2.5-3.5” (6-9 cm) across.

Management 

Common sunflower is a very early emerging spring species, so under a winter wheat crop, for example, few seedlings will successfully emerge or be a problem (A. Dille, personal communication).  The dense canopy of winter wheat and spring canola during the period when common sunflower usually emerges suppresses emergence (Anderson 2007).  Also, winter grains are harvested before most common sunflower seeds are mature, so these crops will tend to reduce the population.  On the other hand, in no-till summer crops, sunflower will emerge before corn, soybean, or grain sorghum are planted, so it needs to be managed at that time, or it will become a serious problem in those crops (A. Dille, personal communication). 

For bad infestations, capture the seeds in the combine and separate them from the crop afterward.  Common sunflower seeds have a high oil content (Seiler 1983) and captured seeds could be a potential fuel source.  Alternatively, the seeds could be ground to destroy viablility and fed to livestock.  Grazing cattle on infested grain stubble can reduce seed production.  Avoiding fall tillage is critical for managing common sunflower since incorporating seeds in soil protects them from seed predators.  The relatively large, oily seeds are highly favored by quail and small mammals and these animals frequently destroy most surface seeds over the winter.  This greatly reduces the density of seedlings emerging the next spring (Cummings and Alexander 2002).  Although seeds can potentially survive for many years in the soil, few actually do so.  Consequently, using the methods above to reduce input to the seed bank for even a single year can bring a severe infestation down to manageable levels.  Hand roguing escaped sunflowers is effective for preventing increase of low level infestations in row crops (Burnside et al. 1981).

The seedlings are large, fast growing and can emerge from deep in the soil.  Consequently, rotary hoes are relatively ineffective against this weed.  Tine weeding should be aimed at breaking or burying the seedlings.  If common sunflower plants between rows get large, avoid using shovels on flexible S-shanks.  These will tend to walk around the strong tap roots and leave the plants in place.  Instead, use sharp sweeps fixed at a shallow angle and run about 1.5-2” deep to sever the shoot from the root.  New shoots cannot sprout from root tissue alone.  The large nutrient storage in the seeds allows seedlings to penetrate even thick layers of mulch.

Common sunflower hybridizes freely with the domesticated sunflower, allowing potential introduction of genes for disease and insect resistance from cultivars.  This may increase survival, reproduction and competitive ability of the weed (Snow et al. 2000).

Ecology

Origin and distribution:  Common sunflower is native to western North America (Heiser 1969).  It now occurs throughout the U.S.A., including Hawaii and Alaska, and in much of Canada and Mexico (Stevens, no date).  It has been introduced into the Carribean (USDA Plants), South America, the Middle East and parts of southern Asia (Holm et al. 1979).   

Seed weight:  6.6 mg (Stevens 1932), 7-9 mg (Teo-Sherrell et al. 1996), 7.1 mg (Alexander et al. 2001), 6.5-7.6 mg (Snow et al. 1998).  Seeds produced from many populations grown in Kansas averaged 7.8-8.7 mg per seed from early July to mid-August and then declined to 4.3 mg in early October (Seiler 1983).  Seeds of an Argentine weedy agricultural biotype averaged 27.1 mg whereas an agrestal biotype averaged 11.3 mg (Casquero and Cantamutto 2016).

Dormancy and germination:  Viability of common sunflower seeds is sometimes as low as 72% (Burnside et al. 1981), but can be as high as 94-99% (Cummings et al. 2002).  Seeds are dormant when mature (Teo-Sherrell et al. 1996, Oracz et al. 2007).  After a few months of dry after-ripening or overwinter burial in cold, moist soil, most seeds become capable of germination (Teo-Sherrell et al. 1996, Mercer et al. 2006, Oracz 2007), but 26 to 42% may still remain dormant (Teo-Sherrell et al. 1996, Mercer et al. 2006).  Shallow burial of the seeds over the winter greatly increases germination the following spring (Burton et al. 2004).  Some seeds will germinate at 39 °F (4 °C), (Putnam et al. 1990), but germination is faster and more complete at 68-77 °F (20-25 °C) (Oracz et al. 2007).  Light is not required for germination (Oracz et al. 2007).  Germination is not reduced by pH as low as 4 or as high as 10, and some seeds will germinate in water containing 10,000 ppm salt (Evetts and Burnside 1972).

Seed longevity:  A few seeds survived at least 17 years when buried at 8” (20 cm) and left undisturbed (Burnside et al. 1996).  Soil burial in the autumn after seed dispersal greatly facilitated formation of a persistent seed bank (Moody-Weis and Alexander 2007).  Seed mortality rates can vary greatly from year to year (Alexander and Schrag 2003).  Average mortality rates for seeds buried for two to four years range from 26 to 47% per year (Teo-Sherrel et al. 1996, Alexander and Schrag 2003).  Mortality of seeds in the soil is low through the first winter (Teo-Sherrell et al. 1996, Burton et al. 2004), but most seeds on the soil surface do not survive the winter (Robel and Slade 1965, Moody-Weis and Alexander 2007) and very few seeds persist on the soil surface for more than two years (Alexander and Schrag 2003).  

Season of emergence:  In the northern Great Plains, seedlings emerge from late April to early June, with most emerging in May (Anderson 2007, Robinson 1978, Teo-Sherrell 1996).  In Kansas they emerge from late March through early May (Mercer et al. 2011).  Seeds from a Kansas population tested at sites across the Midwest showed most emergence occurred during a roughly two-week period with peak emergence from late March to early May.  The timing of emergence depended on soil temperature and moisture and varied substantially between years at a given site (Clay et al 2014).  Warmer winters prolong the period over which seedlings emerge relative to cooler winters (Clay et al. 2014).

Emergence depth:  Seedlings can emerge from depths of at least 4” (10 cm) (CDFA). 

Photosynthetic pathway:  C3 (Bremner et al. 1986) 

Sensitivity to frost:  Seedlings in the cotyledon stage can survive temperatures as low as 23 °F (-5 °C) and mature plants can survive down to 28 °F (-2 °C) (Putnam et al. 2000).

Drought tolerance:  Common sunflower is moderately drought tolerant (USDA Plants).  The main taproot can reach a depth of 10 ft (3 m), which allows established plants to extract water from deep in the soil where few other plant roots can reach (Duke 2001, Bremner et al. 1986, Nielsen 1998).

Mycorrhizae:  Common sunflower has a high mycorrhizal infection rate (Dhillion and Friese 1994).  In domestic sunflower, high mycorrhizal infection improve P uptake and growth.  Production of domestic sunflower can be lower following non-mycorrhizal crops such as canola (Blamey et al. 1997), and the weed may respond similarly.

Response to fertility:  USDA classifies common sunflower as having a low fertility requirement (USDA Plants), but in Argentina it is found only on fertile soils that are high in organic matter and available phosphorus (Cantamutto et al 2008).  It grows on soils with a pH between 5.5 and 7.8 (USDA Plants).  Domesticated sunflower is highly responsive to N, with yields often continuing to increase with application rates in excess of 161 lb N/A (180 kg/ha) (Blamey 1997).

Soil physical requirements:  Common sunflower can grow on soil of fine, medium, and coarse textures (USDA Plants).  It can survive in poor soil, shallow soil over limestone, and mild waterlogging (Duke 2001).  It has medium tolerance to salinity (USDA Plants).

Response to shade:  Common sunflower is intolerant of shade (Stevens, no date).

Sensitivity to disturbance:  No information available.   

Time from emergence to reproduction:  Flowering begins 9 to 17 weeks after emergence (Snow et al. 1998), and continues for 4 to 13 weeks, depending on the population (Seiler 1983).  In the central Great Plains, common sunflower flowers from July to October, and seeds mostly disperse from September through October (Robel and Slade 1965) though some may continue to disperse through the winter (Moody-Weis and Alexander 2007).

Pollination:  Sunflowers are self-incompatible (Kane and Rieseberg 2008), and insect pollinated (Duke 2001).

Reproduction:  Three populations growing without crop competition averaged 38 heads per plant, 136 viable seeds per head and 5,300 seeds per plant (Cummings et al. 2002).  In another study, a typical plant growing with minimal competition produced 7,200 seeds, but some of these were immature whereas others had already shattered (Stevens 1932).  An Argentine biotype grown in competition with domestic sunflower averaged 34 heads/plant, 190 seeds/head, and 6,500 seeds/plant (Casquero and Cantamutto 2016).   

Dispersal:  The seeds are dispersed locally by birds and small mammals (Heiser et al. 1969).  They also disperse in surface irrigation water (Wilson 1980).  Combine harvesters contribute to expansion of patches of common sunflower (Humston et al. 2005) and may also occasionally move seeds to previously uncolonized fields.  The species is common along roadsides and seeds are probably moved to new locations when soil is removed from road ditches.  Seeds probably also move in soil clinging to tires and machinery.

Common natural enemies:  Insects, birds, and small mammals eat many sunflower seeds (Duke 2001).  In one study, 42% of seeds left on the soil surface were eaten in the first 10 days (Alexander et al. 2001).  Red sunflower seed weevil (Smicronyx fuivus), gray sunflower seed weevil (S. sordidus), sunflower moth (Homeosoma electellum), banded sunflower moth (Cochylis hospes), and sunflower budworm (Sulemia helianthana) damaged 44 to 58% of heads, but less than 2% of seeds in some common sunflower populations in Kansas (Cummings et al. 1999).  Many of the diseases and insects of domestic sunflower (Putnam et al. 2000) probably also attack common sunflower.  

Palatability:   Seeds are edible for humans and livestock.  Common sunflower is acceptable forage at all stages of development, but should not be used as the sole feed due to a high Ca/P ratio (Seiler 1986).    

References:

  • Alexander, H. M., C. L. Cummings, L. Kahn, and A. A. Snow.  2001.  Seed size variation and predation of seeds produced by wild and crop-wild sunflowers.  American Journal of Botany 88:623-627.
  • Alexander, H. M., and A. M. Scharg.  2003.  Role of seed banks, and newly dispersed seeds in population dynamics of the annual sunflower, Helianthus annuus.  Journal of Ecology 91:987-998.
  • Anderson, R. L.  2007.  Crop sequence and no-till reduce seedling emergence of common sunflower (Helianthus annuus) in following years.  Weed Science 21:355-358.
  • Blamey, F. P. C., R. K. Zollinger, and A. A. Schneiter.  1997.  Sunflower production and culture.  In Sunflower Technology and Production, A. A. Schneiter, ed., pp. 595-670.  American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America: Madison, Wisconsin.
  • Bremner, P. M., G. K. Preston, and C. F. de St. Grath.  1986.  A field comparison of sunflower (Helianthus annuus) and sorghum (Sorghum bicolor) in a long drying cycle. I. Water extraction.  Austalian Journal of Agricultural Research 37:483-493. 
  • Burnside, O. C., C. R. Fenster, L. L. Evetts, and R. F. Mumm.  1981.  Germination of exhumed weed seed in Nebraska.  Weed Science 29:577-586.
  • Burnside, O. C., R. G. Wilson, S. Weisberg, and K. G. Hubbard.  1996.  Seed longevity of 41 weed species buried 17 years in eastern and western Nebraska.  Weed Science 44:74-86.
  • Burton, M. G., D. A. Mortensen, D. B. Marx, and J. L. Lindquist.  2004.  Factors affecting the realized niche of common sunflower (Helianthus annuus) in ridge-tillage corn.  Weed Science 52:779-787.
  • Cantamutto, M., M. Poverene, and N. Peinemann.  2008.  Multi-scale analysis of two annual Helianthus species naturalized in Argentina.  Agriculture, Ecosystems and Environment 123:69-74.
  • Casquero, M., amd M. Cantamutto.  2016.  Interference of the agrestal Helianthus annuus biotype with sunflower growth.  Weed Research 56:229–236.
  • Clay, S. A., A. Davis, A. Dille, J. Lindquist, A. H.M. Ramirez, C. Sprague, G. Reicks, and F. Forcella.  2014.  Common sunflower seedling emergence across the U.S. Midwest.   Weed Science 62:63-70.
  • Cummings, C. L., and H. M. Alexander.  2002.  Population ecology of wild sunflowers: effects of seed density and post-dispersal seed predators.  Oecologia 130:274-280.
  • Cummings, C. L., H. M. Alexander, and A. A. Snow.  1999.  Increased pre-dispersal seed predation in sunflower crop-wild hybrids.  Oecologia 121:330-338.
  • Cummings, C. L., H. M. Alexander, A. A. Snow, L. H. Riesberg, M. J. Kim, and T. M. Culley.  2002.  Fecundity selection in a sunflower crop-wild study: can ecological data predict crop allele changes?  Ecological Applications 12:1661-1667.
  • CDFA.  Common sunflower, Helianthus annuus.  Encycloweedia: Data Sheets, California Department of Food and Agriculture. http://www.cdfa.ca.gov/PHPPS/IPC/weedinfo/helianthus.htm
  • Dhillion, S. S., and C. F. Friese.  1994.  The occurrence of mycorrhizas in prairies: Applications to ecological restoration.  Thirteenth North American Prairie Conference 13:103-114.
  • Duke, J. A.  2001.  Handbook of Nuts.  CRC Press: Boca Raton, FL. 
  • Evetts, L. L., and O. C. Burnside.  1972.  Germination and seedling development of common milkweed and other species.  Weed Science 20:371-378.
  • Heiser, C. B., Jr., D. M. Smith, S. B. Clevenger, and W. C. Martin, Jr.  1969.  The North American sunflowers (Helianthus).  Memoirs of the Torrey Botanical Club 22:1-218.
  • Holm, L., J. V. Pancho, J. P. Herberger, and D. Plucknett.  1979.  A Geographical Atlas of World Weeds.  Wiley: New York.
  • Humston, R., D. A. Mortensen, and O. N. Bjørnstad.  2005.  Anthropogenic forcing on the spatial dynamics of an agricultural weed: the case of the common sunflower.  Journal of Applied Ecology 42:863–872.
  • Kane, N. C., and L. H. Rieseberg.  2008.  Genetics and evolution of weedy Heliahnthus annuus populations: adaptation of an agricultural weed.  Molecular Ecology 17:384-394.
  • Mercer, K. L., R. G. Shaw , and D. L. Wyse.  2006.  Increased germination of diverse crop – wild hybrid sunflower seeds.  Ecological Applications 16:845-854.
  • Mercer, K. L., H. M. Alexander, and A. A. Snow.  2011.  Selection on seedling emergence timing and size in an annual plant, Helianthus annuus (common sunflower, Asteraceae).  American Journal of Botany 98:075-985.
  • Moody-Weis, J., and H. M. Alexander.  2007.  The mechanisms and consequences of seed bank formation in wild sunflowers (Helianthus annuus).  Journal of Ecology 95:851-864. 
  • Nielsen, D. C.  1998.  Sunflower water use relationships.  Conservation Tillage Fact Sheet #1-98.  USDA-NRCS, USDA-ARS, and Colorado Conservation Tillage Association:Akron, Colorado.  http://www.ars.usda.gov/SP2UserFiles/Place/54070000/1990-1999documents/342%201998%20Nielsen%20FS.pdf
  • Oracz, K., H. E-M. Bouteau, J. M. Farrant, K. Cooper, M. Belghazi, C. Job, D. Job, F. Corbineau, and M. Bailly.  2007.  ROS production and protein oxidation as a novel mechanism for seed dormancy alleviation.  The Plant Journal 50:452-465.
  • Putnam, D.H., E.S. Olinger, D. R. Hicks, B. R. Durgan, D. M. Noetzel, R. A. Meronuck, J. D. Doll, and E. E. Schulte.  1990.  Sunflower.  Alternative Field Crops Manual.  University of Wisconsin-Extension, Cooperative Extension, University of Minnesota: Center for Alternative Plant & Animal Products and the Minnesota Extension Service.  http://www.hort.purdue.edu/newcrop/afcm/sunflower.html.
  • Robel, R. J., and N. A. Slade.  1965.  The availability of sunflower and ragweed seeds during fall and winter.  The Journal of Wildlife Management 29:202-206.
  • Robinson, R. G.  1978.  Control by tillage and persistence of volunteer sunflower and annual weeds.  Agronomy Journal 70:1053-1056.
  • Seiler, G. J.  1983.  Effect of genotype, flowering date, and environment on oil content and oil quality of wild sunflower seed.  Crop Science 23:1063-1068.
  • Seiler, G. J.  1986.  Forage quality of selected wild sunflower species.  Agronomy Journal 78:1059-1064.
  • Snow, A. A., L. H. Riesberg, H. M. Alexander, C. L. Cummings, and D. Pilson.  2000.  Assessment of gene flow and potential effects of genetically engineered sunflowers on wild relatives.  The Biosafety Results of Field Tests of Genetically Modified Plants and Microorganisms, 5th International Symposium, Braunsweig, Germany, 6-10 Sep. 1998., J. Schiemann ed., pp 19-25.  Parey: Berlin.
  • Snow, A. A., P. Moran-Palma, L. H. Riesberg, A. Wszelaki, and G. J. Seiler.  1998.  Fecundity, phenology, and seed dormancy of F1 wild-crop hybrids in sunflower (Helianthus annuus, Asteraceae).  American Journal of Botany  85:794-801.
  • Stevens, M.  No date.  Annual sunflower, Helianthus annuus L.  Plant Guide. USDA NRCS National Plant Data Center.  Download. In USDA Plants. Database.  Natural Resources Conservation Service. http://plants.usda.gov
  • Stevens, O. A.  1932.  The number and weight of seeds produced by weeds.  American Journal of Botany 19:784-794.
  • Teo-Sherrell, C. P. A.  1996.  The fates of weed seeds.  PhD dissertation.  University of Nebraska: Lincoln NE.
  • Teo-Sherrell, C. P. A., D. A. Mortensen, and M. E. Keaton.  1996.  Fates of seeds in soil: a seeded core method of study.  Journal of Applied Ecology 33:1107-1113.
  • USDA Plants Database.  Natural Resources Conservation Service.  http://plants.usda.gov.
  • Wilson, R. G., Jr.  1980.  Dissemination of weed seeds by surface irrigation water in western Nebraska.  Weed Science 28:87-92.