Perennial sowthistle

Sonchus arvensis L.

Perennial sowthistle clasping the stem
Perennial sowthistle flowering plant
Young shoots of the perennial sowthistle

Images above: Upper Left: Perennial sowthistle leaves clasping the stem (Randall Prostak, University of Massachusetts). Upper Right: Perennial sowthistle flowering plant (Randall Prostak, University of Massachusetts) Bottom: Young shoots of perennial sowthistle (Antonio DiTommaso, Cornell University).

Identification

Other common names:  corn sow-thistle, field sowthistle, creeping sow thistle, gutweed, milk thistle, field milk thistle, swine-thistle, tree sow-thistle, dindle, marsh sowthistle

Family:  aster family, Asteraceae

Habit:  Erect, mostly unbranched, perennial herb arising from a basal rosette and spreading by shallow, thickened storage roots.

Description:  Seedlings have short-lived, slightly fleshy, 0.2-0.3” (0.5-0.8 cm) long by 0.05-0.2” (0.13-0.5 cm) wide, round or oval cotyledons with a small notch at the tip.  First true leaves are paddle shaped, irregularly toothed along the margins and dull blue-green.  Young leaves form a rosette and are lance shaped, alternate, and hairless, with prickly teeth along the margins and leaf stalks.  Teeth point towards the base of the leaf.  All parts exude a white sap when injured.  Mature plants are 2-5 ft (0.6-1.5 m) tall, with hollow stems that may branch at the top.  Stems are hairless towards the base, with sparse to dense gland-tipped hairs towards the top, or the top is occasionally hairless.  Leaves are lance-shaped, 2-16” (5-40 cm) long by 1-4” (2.5-10 cm) wide, alternate, hairless, and irregularly lobed.  Leaf margins are toothed and prickly.  Leaves are larger and more densely arranged on the lower stem.  Lower leaves have 2-6 triangular to lance shaped lobes or are occasionally unlobed.  Lobes on the upper leaves are reduced or absent.  Leaf bases have a pair of rounded lobes which clasp the stem.  The root system is extensive, and can reach up to 10 ft (3 m) in depth and spread over 9 ft (2.8 m) horizontally.  Roots are yellow-white, thick, brittle, and fleshy, with buds that can produce vegetative shoots from up to 20” (51 cm) below ground.  Small clusters of flower heads develop at the end of upper stems and branches.  Each bright yellow, dandelion-like flower head is 1-2” (2.5-5 cm) wide.  At the base of each flower head are overlapping, narrow bracts.  Each bract is 0.5-1” (1.3-2.5 cm) long, with many short, yellow gland-tipped hairs (occasionally hairless).  The apparent seed includes a thin, tight coat of fruit tissue.  These seeds are red-brown to dark brown, rectangular, 0.1-0.14” (0.25-0.36 cm) long by 0.04-0.06” (0.1-0.15 cm) wide, and have 5-12 longitudinal ridges.  Each seed is attached to a feathery, white 0.4-0.6” (1-1.5 cm) long pappus. 

Similar species:  Prickly lettuce (Lactuca serriola L.), annual sowthistle (Sonchus oleraceus L.) and spiny sowthistle [Sonchus asper (L.) Hill] are similar to perennial sowthistle.  Prickly lettuce seedlings are hairy, and leaves of mature plants have a distinctive row of sharp spines along the underside of the mid-vein.  Annual and spiny sowthistle flower heads are only 0.75” (2 cm) or smaller, and the seeds have fewer ridges than those of perennial sowthistle.  Spiny sowthistle leaves have larger, spinier teeth than perennial sowthistle leaves, while annual sowthistle leaves lack prickles.  Annual sowthistle leaves usually have a large triangular terminal lobe that is not found in the other two sowthistle species.  All three species are annuals and have taproots, rather than the extensive root system of perennial sowthistle. 

Management

Because perennial sowthistle thrives best in wet soils, improving soil drainage can improve control.  In particular, improving soil drainage will improve the ability of crops to competitively suppress this weed.  

As with most wandering perennial weeds, good control involves fragmenting the root system to weaken subsequent regrowth, repeated killing of the shoots, and strong competition from crops.  In Scandinavian studies, weight and carbohydrate storage in the roots reached a minimum in late May and this corresponded to the 5-7 leaf stage of development (Håkansson 1969).  Burial of the plant at that stage reduced the number of shoots produced the rest of the season relative to burial earlier or later (Håkansson 1969).  Subsequently turning new shoots under two to three times when they reached 4-6 leaves killed the storage roots completely (Håkansson 1969, Håkansson and Wallgren 1972a).  Performing the operations at the 4-leaf stage eliminated the plants in 74 days or less but required one to three additional operations, whereas waiting until the 6-leaf stage required up to 84 days but only required one to two additional operations.  The resulting root fragments reached the 4-6 leaf stage in about 2 to 3 weeks and this corresponded to the point at which the root fragments were most depleted (Håkansson and Wallgren 1972a).  Similar to the tillage experiments, cutting the shoots off just below soil level when they reached the 6-leaf stage eliminated the storage roots in three operations, whereas cutting the shoots at 4 leaves required four operations (Håkansson and Wallgren 1972a).  Waiting until the plants had 6 leaves caused shrinkage of the storage roots but not complete death in one experiment, but produced the most rapid elimination of the plants (42 days) in another experiment. 

In general, a well-planned tillage fallow period can eliminate the weed in time to plant a winter grain or late season vegetable crop.  Spring plowing is more effective than autumn plowing for control of perennial sowthistle (Brandsæter et al. 2017).  Fallow tillage in the fall is less effective than tillage in the spring because the buds become dormant and do not sprout readily in the fall (Andersson et al. 2013, Håkansson and Wallgren 1972a, Tørresen et al. 2010, Brandsӕter et al. 2010).  Nevertheless, tillage following grain harvest can be a useful control tactic because it kills topgrowth that is feeding the storage roots and because breaking up the storage roots makes the plants less vigorous in the spring (Vanhala 2006, Anbari et al. 2011).   Two years of hay mowed three times per season also substantially reduces perennial sowthistle density (Vanhala et al. 2006). 

As with most perennial weeds, cutting up the roots with tillage implements greatly decreases the vigor of the subsequent shoots (Håkansson and Wallgren 1972b, Anbari et al. 2011).  Moreover, burying the small fragments 8-12” (20-30 cm) deep also reduces the number and subsequent vigor of the shoots (Håkansson and Wallgren 1972b).  Thus, some European organic growers control the weed by chopping the storage roots into small pieces with a disk or field cultivator and then moldboard plowing to bury the fragments (Anbari et al. 2011).  When the shoots from deeply buried small fragments were allowed to grow unchecked, they produced large storage roots by the end of the season so that chopping up and burying the roots was essentially futile if no further actions were taken (Håkansson and Wallgren 1972b).  When fields were planted with barley, however, the combination of fragmentation, deep burial and crop competition resulted in a substantial decrease in weight of storage roots.  A short tilled fallow period could probably be substituted for the deep tillage in this control strategy. 

Ecology

Origin and distribution:  Perennial sowthistle is native to Europe and western Asia, and is most common in northwestern Europe.  It has been introduced into North and South America, Australia and New Zealand.  It is distributed throughout the northern U.S.A. and southern Canada but only occurs sporadically in the southern and southwestern states.  (Lemna and Messersmith 1990)

Seed weight:  Mean 0.6 mg, range 0.38-0.69 mg (EFBI); 0.38-0.5 mg (Stevens 1932).

Dormancy and germination:  Seeds have little or no innate dormancy and will readily germinate immediately after dispersal (Lemna and Messersmith 1990).  Seeds germinate best at 77-86 °F (25-30 °C).  Few seeds will germinate at constant temperature outside this range, but fluctuating temperatures with the high above 86 °F (30 °C) increase germination (Håkansson and Wallgren 1972a).  Many perennial sowthistle seeds will germinate in the dark, but exposure to light increases the germination (Lemna and Messersmith 1990).  Seeds can tolerate wetting for 5 days and subsequent drying without losing viability (Lemna and Messersmith 1990).

Seed longevity:  Few seeds last in the soil longer than 5 years (Chepil 1946).  Most seeds (80%) germinate within the first year (Lemna and Messersmith 1990).  Seeds apparently survive better in clay soils than in sandy loam (Chepil 1946).  In soil worked three times a year, mortality of seeds was 48-65% per year (Roberts and Neilson 1981).

Season of emergence:  Seedlings emerge primarily in late spring thru mid-summer (Chepil 1946, Håkansson and Wallgren 1972a).  Shoots begin emerging from rootstocks as soon as the soil warms, which is late April in many of the areas where the weed is a major pest (Doll 2002, Håkansson 1969). 

Emergence depth:  Seedlings emerge best from the top 0.2” (0.5 cm) of soil, though a very few can emerge from as deep as 1.2” (3 cm) (Håkansson & Wallgren 1972a).  Root fragments can produce shoots from anywhere in the plowed horizon, but emergence from fragments at the soil surface or deeper than 8” (20 cm) is reduced (Håkansson and Wallgren 1972b).  Shoots from small, deeply buried fragments are weaker and may not emerge at all.

Photosynthetic pathway:  C3 (Lemna and Messersmith 1990)

Sensitivity to frost:  Shoots die back after frost (Håkansson 1969, Lemna and Messersmith 1990, Stevens 1924).  Overwintering roots survive soil temperatures as low as 3 °F (-16 °C) without damage, but cannot survive -4 °F (-20 °C) (Lemna and Messersmith 1990).

Drought tolerance:  Perennial sowthistle seedlings are highly sensitive to drying, and generally only establish in wet spots or in areas where crop residues or cover of other plants keep the soil moist.  Plant growth is best in saturated soil and progressively reduced at field capacity and lower soil moisture levels (Zollinger and Kells 1991).  Well established plants, however, often have deep roots that help the plant survive dry periods.  (Lemna and Messersmith 1990)

Mycorrhiza:  There have been two reports of the presence of mycorrhiza on this species and one report of their absence (Harley and Harley 1987).

Response to fertility:  Nitrogen has little influence on shoot emergence, but increases the mass of thickened roots by fall (Håkansson and Wallgren 1972b).  The species accumulates higher N, P, K, and Mg concentrations than winter wheat and higher K and Ca concentrations than spring barley (Lemna and Messersmith 1990).  It can achieve K tissue concentrations of 5%.  Perennial sowthistle does best on neutral to slightly alkaline soils (Lemna and Messersmith 1990).  Plant growth was optimum at pH 6.2 and 7.2, but 30% lower at pH 5.2 (Zollinger and Kells 1991).

Soil physical requirements:  Perennial sowthistle is most common on loam or clay soils, particularly in areas with high precipitation, and is relatively rare on dry, sandy and gravelly soils.  Compaction reduces its growth and ability to produce new shoots.  The species tolerates moderate salinity, but only in wet soils.  (Lemna and Messersmith 1990)

Response to shade:  Perennial sowthistle is sensitive to shade.  Plant weight and reproduction are reduced in shade, and leaf growth increases at the expense of stems and roots as shade increases.  (Zollinger and Kells 1991)

Sensitivity to disturbance:  Young plants develop the capacity to re-establish if the root is fragmented within a few weeks after emergence.  Basal stems and new roots growing from established plants have the same capacity for vegetative reproduction (Håkansson 1969, Håkansson and Wallgren 1972a).  Most of the thickened roots from which new plants arise lie within the top 8” (20 cm) plow layer where they can be broken up by tillage implements.  This creates more, but weaker, sprouts.  Deep burial of root fragments by inversion tillage reduces the number and vigor of subsequent sprouts.  Thickening of new roots into overwintering storage roots begins when the shoot has 5-7 leaves.  Buds on storage roots become dormant in late summer and fall, so tillage late in the season does not induce a flush of new shoots (Andersson et al. 2013, Brandsæter et al. 2010, Håkansson 1969, Håkansson and Wallgren 1972a).  Bud dormancy is enhanced primarily by shortening daylength, but maximally in combination with temperatures below 62 °F (17 °C) (Liew et al. 2012, Taab et al. 2018).  Bud dormancy is overcome by exposure to 36-40 °F (2-5 °C) for a month or more (Brandsæter et al. 2010, Håkansson and Wallgren 1972a, Taab et al. 2018).

Time from emergence to reproduction:  Most plants do not flower during their first year unless conditions are highly favorable (Lemna and Messersmith 1990).  Flowering begins when the shoot has 12-15 leaves (Håkansson 1969), which is in early July in the northern U.S.A. (Doll 2002).  Flowering continues until late summer (Håkansson 1969).  Initiation of flowering is delayed several weeks by soil moisture below field capacity and by shading (Zollinger and Kells 1991).  Seeds develop about 10 days after the flowers open (Lemna and Messersmith 1990).

Pollination:  Perennial sowthistle is pollinated by bees, flies and blister beetles.  The species does not self pollinate, and thus populations consisting of a single clone do not produce seeds.  (Lemna and Messersmith 1990)

Reproduction:  Perennial sowthistles produce an average of about 30 seeds per head (Lemna and Messersmith 1990).  A particularly large, isolated shoot reportedly produced 62 seed heads and nearly 10,000 seeds (Stevens 1932), but in our experience 5-20 seed heads is more typical of plants growing in agricultural fields.  Seeds can mature on cut stems once the flowers are pollinated (Lemna and Messersmith 1990).  Spreading roots are the primary means of vegetative reproduction and enable plants to spread rapidly (Lemna and Messersmith 1990).  The edges of clones of perennial sowthistle in North Dakota spread outward at a rate of 1.6-9.2 ft per year (0.5-2.8 m per year) (Lemna and Messersmith 1990). 

Dispersal:  Tufts of hairs help wind disperse seeds moderate distances, but seeds probably rarely disperse further than the adjacent field by wind.  Hooked cells on the hairs cause the seeds to cling to fur and clothing.  The species also spreads in contaminated seed and hay, and in combines.  Since storage roots are mostly in the plow layer, root fragments probably disperse in soil clinging to tillage machinery.  (Lemna and Messersmith 1990)

Common natural enemies:  Perennial sowthistle is susceptible to several nematodes including root-knot nematode (Meloidogyne incognita) and cyst nematode (Heterodera sonchophila).  It also is susceptible to Pseudomonas solanacearum wilt, but plants typically recover from wilting symptoms in the evening.  Although several insect species have been explored for biological control of perennial sowthistle, none have demonstrated significant impact on populations of this species.  (Lemna and Messersmith 1990)

Palatability:  The leaves have sometimes been eaten as a salad or pot herb (Lemna and Messersmith 1990).  Perennial sowthistle is acceptable quality forage for most livestock, but not lambs (Lemna and Messersmith 1990). 

References:

  • Andersson, L., U. Boström, J. Forkman, I. Hakman, J. Liew, and E. Magnuski.  2013.  Sprouting capacity from intact root systems of Cirsium arvense and Sonchus arvensis decrease in autumn.  Weed Research 53:183-191.
  • Anbari, S., A. Lundkvist, and T. Verwijst.  2011.  Sprouting and shoot development of Sonchus arvensis in relation to initial root size.  Weed Research 51:142-150.
  • Brandsӕter, L. O., H. Fogelfors, H. Fykse, E. Graglia, R. K. Hensen, B. Melander, J. Salonen, and P. Vanhala.  2010.  Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens.  Weed Research 50:102-109.
  • Brandsæter, L.O., K. Mangerud, M. Helgheim, and T.W. Berge.  2017.  Control of perennial weeds in spring cereals through stubble cultivation and mouldboard ploughing during autumn or spring.  Crop Protection 98:16-23.
  • 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.
  • Doll, J.  2002.  Knowing when to look for what: Weed emergence and flowering sequences in Wisconsin.  http://128.104.239.6/uw_weeds/extension/articles/weedemerge.htm. 
  • EFBI.  Ecological Flora of the British Isles.http://ecoflora.org.uk/.
  • Lemna, W. K. and C. G. Messersmith.  1990.  The biology of Canadian weeds. 94. Sonchus arvensis L.  Canadian Journal of Plant Science 70:509-532.
  • Liew, J., L. Andersson, U. Boström, J. Forkman, I. Hakman, and E. Magnuski.  2012.  Influence of temperature and photoperiod on sprouting capacity of Cirsium arvense and Sonchus arvensis root buds.  Weed Research 52:449-457.
  • Håkansson, S.  1969.  Experiments with Sonchus arvensis L. I. Development and growth, and response to burial and defoliation in different developmental stages.  Lantbrukshögskolans Annaler 35: 989-1030.
  • Håkansson, S. and B. Wallgren.  1972a.  Experiments with Sonchus arvensis L. II. Reproduction, plant development and response to mechanical disturbance.  Swedish Journal of Agricultural Research 2:3-14.
  • Håkansson, S. and B. Wallgren.  1972b.  Experiments with Sonchus arvensis L. III. The development from reproductive roots cut into different lengths and planted at different depths, with and without competition from barley.  Swedish Journal of Agricultural Research 2:15-26.
  • Harley, J. L. and E. L. Harley.  1987.  A check-list of mycorrhiza in the British flora.  New Phytologist 105:1-102.
  • Roberts, H. A., and J. E. Neilson.  1981.  Seed survival and periodicity of seedling emergence in twelve weedy species of Compositae.  Annals of Applied Biology 97:325-334.
  • Stevens, O. A.  1924.  Some effects of the first fall frost.  The American Midland Naturalist 9:14-17.
  • Stevens, O. A.  1932.  The number and weight of seeds produced by weeds.  American Journal of Botany 19:784-794.
  • Taab, A., L. Andersson, and U. Boström.  2018.  Modelling the sprouting capacity from underground buds of the perennial weed Sonchus arvensis.  Weed Research 58:348–356.
  • Tørresen, K. S., H. Fykse, and T. Rafoss.  2010.  Autumn growth of Elytrigia repens, Cirsium arvense and Sonchus arvensis at high latitudes in an outdoor pot experiment.  Weed Research 50:353-363.
  • Vanhala, P., T. Lötjönen, T. Hurme, and J. Salonen.  2006.  Managing Sonchus arvensis using mechanical and cultural methods.  Agriculture and Food Science 15:444-458.
  • Zollinger, R. K., and J. J. Kells.  1991.  Effect of soil pH, soil water, light intensity, and temperature on perennial sowthistle (Sonchus arvensis L.).  Weed Science 39:376-384.