Flixweed

Descurainia sophia (L.) Webb ex Prantl

Flixweed foliage
Flixweed plant in flower
Flixweed seed pods

Images above: Upper left: Flixweed foliage (Joseph DiTomaso, University of California, Davis). Upper right: Flixweed plant in flower (Joseph DiTomaso, University of California, Davis). Bottom: Flixweed seed pods (Joseph DiTomaso, University of California, Davis).

Identification

Other common names:  herb sophia, tansy mustard

Family:  mustard family, Brassicaceae

Habit:  Slender, erect, branching, winter annual or biennial herb.

Description:  Seedlings have light green cotyledons 0.2-0.3” (0.5-0.7 cm) long by 0.04-0.06” (0.1-0.15 cm) wide, oval to club shaped, and rough due to surface hairs.  The seedling stem is short and sparsely hairy.  The first true leaves are opposite on the stem, usually tri-lobed, stalked, and hairy.  All subsequent leaves are alternate and subdivided into leaflets.  Leaflets have many narrow, closely spaced lobes.  Seedling leaves are 0.13-0.3” (0.3-0.8 cm) long, and develop into a basal rosette that withers during flowering.  Stem and leaves have star shaped hairs.  The mature plant bolts from the rosette; stem height ranges from 8-32” (20-81 cm).  The upper half of the hairy stem has branches up to 15” (38 cm) long.  Stem leaves are 0.75-4” (1-10 cm) long by 0.5-2” (1.3-5 cm) wide, narrowly oval, pinnate, covered in star-shaped hairs, and narrower when located higher on the stem.  Leaflets are narrow oval to linear in shape with pointy tipped lobes.  The taproot is large and sometimes branches.  Flowers are green-yellow to yellow, 0.13” (0.3 cm) wide, upward facing, individually stalked, 4 petaled, and clustered into a triangular group at the stem tip.  Flower stalks are 0.5” (1.3 cm) long and are attached perpendicularly to the stem.  The stem continuously lengthens as new flowers develop at the tip and seeds ripen lower on the stem.  Fruit are long, skinny pods divided by papery, translucent, internal membrane into two chambers.  Pods are green, bluntly round tipped, 0.5-1.25” (1.3-3.2 cm) long by 0.04” (0.1 cm) wide, straight or slightly curved; they turn brown at maturity.  Seeds are thumb to egg-shaped, smooth, dull orange, and 0.02-0.05” (0.05-0.13 cm) long by 0.01-0.02” (0.025-0.05 cm) wide.  Each chamber has a row of 10 to 20 seeds. Seeds are sticky when wet.

Similar species:  Pinnate tansymustard [Descurainia pinnata (Walter) Britton] has less finely divided, lacy looking leaves and shorter fruit at maturity; its seeds are in two rows per pod chamber and the seedling stem is maroon.  Smallflowered bittercress (Cardamine parviflora L.) seedlings have similar rosettes, but their leaves are not subdivided into smaller leaf units with central branches.

Management

If feasible, rotate with summer planted crops to reduce flixweed populations.  In grain-fallow rotations, good control of flixweed in the fallow years is essential.  First tillage with a flat bladed implement should occur before flowers drop.  Otherwise, disk lightly to chop up the plants but, in any case, do not let filled pods form.  Following grain-grain rotations, harrow or disk the field shallowly several times between harvest and winter, and then again in the spring (Best 1977, Halvorson and Guertin 2003).  Plow and plant two weeks later.  Tine weed the grain before emergence and again as soon as the crop will tolerate it (Muenscher 1955).  If further flushes of the weed occur, continue tine weeding until grain stalks begin to elongate.  Consider overseeding with a clover at the last tine weeding.  This will not compete with the crop but will compete with newly emerging flixweed in the fall and allow the soil to rest from excessive tillage.   Flixweed pods often do not shatter until grain harvest so consider trapping chaff to prevent seed return.  Alternatively, capture the flixweed seed with the grain in the combine and separate the two later with a grain cleaner. 

Although flixweed tolerates crop competition better than most annual weeds, a vigorous crop is still an essential component of management.  Ensure that planting density is sufficient to compensate for stand losses that may result from aggressive tine weeding.  Except during drought years, the crop is likely to respond to good soil fertility more than flixweed.  

Ecology

Origin and distribution:  Flixweed is native to Europe and occurs from North Africa to Scandinavia and across Asia to northern India and China.  In North America, it occurs throughout the U.S.A., except parts of the Southeast, and northward in Canada and Alaska to the arctic.  It has also been introduced into South America and New Zealand (Best 1977, USDA Plants).

Seed weight:  0.12 mg (Best 1977, Bond et al. 2007)

Dormancy and germination:  Nearly all flixweed seeds are dormant when shed from the parent plant (Baskin et al 2004, Li et al. 2005).  Germination is limited in the first fall and spring after seed shed, but becomes more plentiful in subsequent years (Baskin et al. 2004).  Dormancy is broken by exposure to summer-like soil temperatures, with optimum day/night temperatures of 77/59 °F (25/15 °C).  However, seed will not germinate at these temperatures, but will wait for cooler temperatures of 59/43 to 68/50 °F (15/6 to 20/10 °C) (Baskin et al. 2004).  This ensures that the main peak in germination occurs during cool weather in the fall after the seeds have experienced summer heat.  Light is a primary requirement for germination; few seeds will germinate in dark regardless of temperature (Baskin et al. 2004, Li et al. 2005, Milberg 1997).  Although some research has shown that a few days of cold (39 °F or 4 °C), wet and darkness can break dormancy (Ali et al. 2010), other research shows that extended periods of such conditions for longer than 5 days can induce secondary dormancy to such an extent that spring germination is limited (Baskin et al. 2004, Li et al. 2005).  This ensures that the seeds will not germinate during extended periods of cold in winter or early spring.  Seeds germinate best with alternating day/night temperatures (Best 1977).  Nitrate breaks dormancy (Ali et al. 2010, Milberg 1997).

Seed longevity:  Flixweed forms a persistent seed bank that declines slowly, even with tillage.  Nearly all seeds remained viable after 30.5 months burial in Sweden (Baskin et al. 2004).  Viable seeds in undisturbed soil in Alaska declined by 25% per year (Conn et al., 2006).  Based on the number of seeds surviving after six years in a spring grain-fallow rotation in Saskatchewan, the rate of decline in tilled soil was 23% in clay, 33% in loam and 32% in sandy loam (Chepil 1946).

Season of emergence:  Flixweed emerges primarily in autumn and early spring (Best 1977), with higher emergence in fall than in spring (Baskin et al. 2004). 

Emergence depth:  As would be expected for a species with small seeds, flixweed seeds must be near the soil surface for seedling emergence (Halvorson and Guertin 2003).

Photosynthetic pathway:  C3 (Halvorson and Guertin 2003)

Sensitivity to frost:  Flixweed will survive well at -13 °F (-25 °C) (Halvorson and Guertin 2003).  It commonly overwinters as a rosette of small leaves; snow cover protects it from cold temperatures and drying winds in far northern latitudes (Best 1977). 

Drought tolerance:  Flixweed requires moist soil (PFAF), and inefficiently uses soil moisture (Best 1977, Halvorson and Guertin 2003).  It is probably abundant in dry regions because of its ability to grow during cool, moist periods of the year.

Mycorrhiza:  Flixweed is not mycorrhizal (Pendleton and Smith 1983).

Response to fertility:  Flixweed shoot growth is relatively unresponsive to N, particularly when growing with a competitive crop (Mahn 1988, Blackshaw et al. 2003).  However, roots increase greatly with increasing N fertility (Blackshaw et al. 2003), which may increase its competitiveness for water in high N soils.  It is relatively unresponsive to P (Blackshaw et al. 2004).  The extensive taproot system of flixweed facilitates the extraction of nutrients from deep layers of the soil (Blackshaw 2004).

Soil physical requirements:  The species grows on a wide range of soils from clay to sand (PFAF, Best 1977), but it is considered an indicator of sandy or stony soils (Best 1977, Bond et al. 2007, Halvorson and Guertin 2003).  It tolerates a wide range of pH (PFAF), and can thrive on calcareous sites that are low in humus (Best 1977).

Response to shade:  Flixweed can grow in semi-shade (Halvorson and Guertin 2003).  It responds to shade by reduced allocation to roots and greater allocation to leaf area, which is typical of shade-tolerant plants (Landau et al. 2017).

Sensitivity to disturbance:  Close mowing reduces seed production (Huffman 2003).

Time from emergence to reproduction:  Overwintering seedlings flower about 4 weeks after resuming growth in spring (Best 1977, Halvorson and Guertin 2003).  Plants emerging in late April in Saskatchewan flowered about one month later, but plants that were not exposed to cold temperatures required several months to reach maturity (Best 1977).  Seeds matured in mid-summer, approximately 6 weeks after the beginning of flowering (Best 1977).

Pollination:  Flixweed normally self-pollinates (Halvorson and Guertin 2003).

Reproduction:  Optimum seed production has been estimated to range from 4,000-7,500 (Mahn 1988) to 76,000 seeds per plant (Best 1977), but an exceptionally large plant produced 700,000 seeds (Salisbury 1961).  In a competitive wheat crop, seed production was reduced to 150-250 seeds per plant (Mahn 1988).

Dispersal: The seeds produce a sticky substance that attaches them to bird feathers (Best 1977). Seeds are spread in contaminated feed and forage (Halvorson and Guertin 2003).  Most seeds die in the rumen (Blackshaw and Rode 1991), but some can pass through and are spread in manure (Halvorson and Guertin 2003).  Seeds are also spread as contaminants of grain and forage seed (Best 1977, Dewey et al. 1985, Halvorson and Guertin 2003).  The seeds survive in water for several years (Comes et al.1978) and disperse in irrigation water (Kelley and Bruns 1975).

Common natural enemies:   Flea beetles, cabbage seedpod weevils and beet leaf hoppers use flixweed as an alternative host, but they have little adverse effect on this species (J. Leeson, personal communication).

Palatability:  The seeds have a high oil and protein content.  Native Americans parched seeds and cooked them into a porridge, made them into bread, or used them to thicken soup (Mitich 1996).  Young plants can be eaten raw, but have a strong odor and bitter taste.  Bitter taste and odor can be removed by boiling for 3-4 minutes with two changes of water (Mitich 1996).  Flixweed is low in palatability for most livestock, but it sometimes forms an important part of the diet of cattle in the Intermountain West (Halvorson and Guertin 2003).  Consumption of mature plants by cattle can cause poisoning (Halvorson and Guertin 2003). 

References:

  • Ali, T., P. Hossein, F. Asghar, Z. Salman, Z. Chahooki, and M. Ali.  2010.  The effect of different treatments on improving seed germination characteristics in medicinal species of Descurainia sophia and Plantago ovata.  African Journal of Biotechnology 9:6588-6593.
  • Baskin, C. C., P. Milberg, L. Andersson, and J. M. Baskin.  2004.  Germination ecology of seeds of the annual weeds Capsella bursa-pastoris and Descurainia sophia originating from high northern latitudes.  Weed Research 44:60-68.
  • Best, K.F.  1977.  The biology of Canadian weeds. 22 Descurainia sophia (L.) Webb.  Canadian Journal of Plant Science. 57:499-507.
  • Blackshaw, R.E.  2004.  Application method of nitrogen fertilizer affects weed growth and competition with winter wheat.  Weed Biology and Management 4:103-113.
  • Blackshaw, R. E., R. N. Brandt, H. H. Janzen, T. Entz, C. A. Grant, and D. A. Derksen.  2003.  Differential response of weed species to added nitrogen.  Weed Science 51:532-539.
  • Blackshaw, R. E., R. N. Brandt, H. H. Janzen, and T. Entz.  2004.  Weed species response to phosphorus fertilization.  Weed Science 52:406-412.
  • Blackshaw, R. E., and L. M. Rode.  1991.  Effect of ensiling and rumen digestion by cattle on weed seed viability.  Weed Science 39:104-108.
  • Bond, W., G. Davies, and R. Turner.  2007.  The biology and non-chemical control of flixweed (Descurainia sophia (L.) Webb ex Prantl.). April 17, 2007. https://www.gardenorganic.org.uk/sites/www.gardenorganic.org.uk/files/organic-weeds/descurainia-sophia.pdf
  • Chepil, W. S.  1946.  Germination of weed seeds. I. Longevity, periodicity of germination, and vitality of seeds in cultivated soil.  Scientific Agriculture 26:307-346.
  • Comes, R. D., V. F. Bruns, and A. D. Kelley.  1978.  Longevity of certain weed and crop seeds in fresh water.  Weed Science 26:336-344.
  • Conn, J. S., K. L. Beattie, and A. Blanchard.  2006.  Seed viability and dormancy of 17 weed species after 19.7 years of burial in Alaska.  Weed Science 54:464-470.
  • Dewey, S. A., D. C. Thill, and P. W. Foote.  1985.  Weed seed contamination of cereal grain seedlots – a drill box survey.  University of Idaho, Cooperative Extension Service, Agricultural Experiment Station, Current Information Series No. 767.
  • Halvorson, W. L. and P. Guertin.  2003.  Fact sheet for Descurainia sophia (L.) Webb ex. Prantl.  U.S. Geological Survey/Southwest Biological Science Center, University of Arizona, Tucson AZ.  http://sdrsnet.srnr.Arizona.edu/data/sdrs/ww/docs/descsoph.pdf.
  • Huffman, L.  2003.  Flixweed - a “new” weed to watch for?  Ontario Ministry of Agriculture, Food and Rural Affairs.
  • Kelley, A. D., and V. F. Bruns.  1975.  Dissemination of weed seeds by irrigation water.  Weed Science 23:486-493.
  • Landau, C. A., B. J. Schutte, A. O. Mesbah, and S. V. Angadi.  2017.  Flixweed (Descurainia sophia) shade tolerance and possibilities for flixweed management using rapeseed seeding rate.  Weed Technology 31:477-486.
  • Li, W., X. Liu, M. A. Khan, Y. Kamiya, and S. Yamaguchi.  2005.  Hormonal and environmental regulation of seed germination in flixweed (Descurainia sophia).  Plant Growth Regulation 45:199-207.
  • Mahn, E.-G.  1988.  Changes in the structure of weed communities affected by agrochemicals – what role does nitrogen play?  Ecological Bulletins 39:71-73.
  • Milberg, P.  1997.  Weed seed germination after short-term light exposure: germination rate, photon fluence response and interaction with nitrate.  Weed Research 37:157-164.
  • Mitich, L.W.  1996.  Flixweed (Descurainia sophia).  Weed Technology 10:974-977.
  • Muenscher, W. C.  1955.  Weeds, 2nd edition.  Cornell University Press: Ithaca, NY.
  • Pendleton, R.L., and B.N. Smith.  1983.  Vesicular-arbuscular mycorrhizae of weedy and colonizer plant species at disturbed sites in Utah.  Oecologia 59:296-301.
  • PFAF.  Plants for a Future Database, Descurania sophia.  https://pfaf.org/User/Plant.aspx?LatinName=Descurainia+sophia
  • Salisbury, E. J.  1961.  Weeds and Aliens.  Collins: London. 
  • USDA Plants Database.  Natural Resources Conservation Service.  http://plants.usda.go