Shepherd's-purse

Images above: Upper Left: Shepherd’s-purse seedling (Scott Morris, Cornell University). Upper Right: Shepherd’s-purse young rosette (Scott Morris, Cornell University). Bottom Left: Shepherd’s-purse plants in flower (Antonio DiTommaso, Cornell University). Bottom Right: Shepherd’s-purse flowers and fruit (Scott Morris, Cornell University).

Identification 

Other common names:  pick-pocket, shepherds-purse, shepherds-bag, pepper plant, case weed, pick-purse, shepherd's bag, shepherd's-pouch, mother's-heart, St. James weed, witches'-pouches, toothwort, shovel-plant

Family:  mustard family, Brassicaceae

Habit:  Erect, winter or summer annual herb arising from a basal rosette.

Description:  The seedling stem is light green to purple.  Cotyledons are oval to spatula-shaped, 0.1-0.25” (0.25-0.6 cm) long by 0.06” (0.15 cm) wide, hairless, and long-stalked.  The first two to four leaves are opposite, round to oval, without teeth or slightly toothed, and densely hairy.  Hairs are short and spreading, with branching star-shaped tips.  Some hairs may be unbranched.  All subsequent leaves are alternate, oval to club-shaped, toothed to deeply lobed (occasionally entire), and form a basal rosette.  The rosette leaves have hairs along the underside of the midvein and are hairless to sparsely hairy above.  Mature plants bolt from the rosette to form a 4-30” (25-76 cm) tall, occasionally branching flowering stem.  The stem is green to purple, hairy towards the base and smooth to sparsely hairy above, and has leaves only on the lower portions.  Rosette leaves are 1.25-6” (3-15 cm) long by up to 1.5” (4 cm) wide, and tapered towards the base.  Leaf shape and hairs are similar to those of the seedling.  Stem leaves are lance-shaped, 0.4-2.2” (1-5 cm) long by up to 0.6” (1.5 cm) wide, alternate, without lobes, stalkless, and may clasp the stem at the base.  The taproot is thin and branching, with fibrous secondary roots.  White, four-petaled flowers continually develop at the tips of the stem and branches.  Each flower is up to 0.25” (0.6 cm) wide, with a 0.3-0.6” (0.8-1.5 cm) long, hairless to sparsely hairy stalk.  Stalks are initially upright, becoming spreading and nearly perpendicular to the stem as old flowers are replaced by flattened, heart-shaped seedpods.  The seedpods are notched at the tip, two-segmented, and 0.2-0.4” (0.5-1 cm) long by 0.1-0.3” (0.25-0.8 cm) wide.  Each seedpod contains 10-20 seeds.  The seeds are oblong, shiny, pale orange to red-brown, and 0.03-0.04” (0.08-0.1 cm) long by 0.01-0.02” (0.025-0.05 cm) wide.

Similar species:  Spreading, star-shaped hairs and heart-shaped seedpods distinguish shepherd’s purse from similar species in the mustard family.  Field pennycress (Thlaspi arvense L.), Virginia pepperweed (Lepidium virginicum L.), and field pepperweed [Lepidium campestre (L.) W.T. Aiton] are all rosette-forming annuals with flattened seed pods.  Field pennycress leaves are hairless with wavy margins, while shepherd’s purse leaves are toothed or lobed.  The flowering stems of Virginia pepperweed and field pepperweed have leaves throughout, while shepherd’s purse has leaves only on the lower parts of the stem.

Management

Shepherd's-purse germinates primarily in the spring and early fall.  A lag between tillage and seedbed preparation at these times of year depletes the seed bank near the soil surface.  Since the seedlings are tiny, tine weeding and other in-row and near row cultivation tools easily kills them.  Since shepherd’s-purse is primarily a cool season species, so rotation with warm season crops like squash and tomato break the life cycle of this weed.  Rapid clean-up of the field after short early-season crops like lettuce and radish will prevent seed set.

Shepherd's-purse is a common weed in winter grain crops.  Since the seedlings are small and fragile early in the plant's life cycle and remain very short until spring, they are highly susceptible to fall harrowing.  Pre-emergence harrowing will break or dry out white thread stage seedlings, and post-emergence harrowing can bury many of the established seedlings. 

Dense planting helps control this weed in crops that will tolerate high density, particularly if the crops are tall since the weed is always short.  A fall forage radish cover crop effectively suppressed establishment of shepherd's-purse in fall and early spring (Lawley et al. 2011).  Emergence and growth may be suppressed by incorporated white mustard (Didon et al. 2014) or buckwheat (Kumar et al. 2008) cover crops.  Organic mulch materials are highly effective for suppressing shepherd’s-purse since the seedlings are small and the leaves remain flat on the ground until flowering.   

Ecology

Origin and distribution:  Shepherd’s-purse originated in the eastern Mediterranean but today it is a cosmopolitan weed found in most temperate regions of the world and at temperate elevations in the tropics and subtropics (Defelice 2001).  The species occurs throughout the U.S.A. and Canada, including the far north (USDA Plants).  Three genetic clusters have been identified, the first occurring in the Middle East, a second in Europe, and the most recent in eastern Asia (Orsucci et al. 2019).  An accession from the U.S.A. was aligned with the Middle Eastern cluster.

Seed weight:  0.087-0.097 mg (Orsucci et al. 2019), 0.10 mg (Doisy et al. 2014, Stevens 1932, Storkey et al. 2010), 0.11 mg (Gardarin et al. 2010, Werle et al. 2014), 0.14 mg (Terpstra 1986).  Heavier seeds tend to have higher germination rates (Orsucci et al. 2019).

Dormancy and germination:  Seeds of shepherd’s-purse are dormant when they ripen and require cold treatment before they can germinate (Baskin and Baskin 1989, Baskin et al. 2004, Hill et al. 2014, Popay and Roberts 1970a, 1970b).  Nitrate may enhance germination (Kumar et al. 2008), particularly in combination with fluctuating temperatures that include chilling (Popay and Roberts 1970a).  Once they are non-dormant, a high percentage of seeds will sprout at day/night temperatures ranging from 59/43 to 86/59 °F (15/6 to 30/15 °C) (Baskin and Baskin 1989, Popay and Roberts 1970a).  Different populations of this species have variable temperature requirements, with some populations having a pronounced temperature optimum and others germinating equally over a wide range of temperatures (Neuffer and Hurka 1988).  Seeds generally require brief exposure to light for germination (Baskin et al. 2004, Popay and Roberts 1970a), except in early spring when some seeds may germinate in the dark (Baskin and Baskin 1989).  Warm soil temperatures greater than 95/68 °F (35/20 °C) will induce complete dormancy, but lower summer temperatures will induce dormancy in only a percentage of the seeds (Baskin and Baskin 1989).  Fall tillage can expose to light seeds that were chilled the previous winter but not exposed to dormancy-inducing summer temperatures.  This allows prolific germination following tillage in late summer or fall (Popay and Roberts 1970b).  Stimulation of germination by tillage may also be explained by release of seeds from high carbon dioxide and low oxygen levels, as occurs beneath the soil surface (Popay and Roberts 1970a).  However, at high latitudes, chilling fall temperatures maintain dormancy of seeds shed in summer and prevent germination during their first fall (Baskin et al. 2004). 

Seed longevity:  Seeds can survive up to 35 years in undisturbed soils (Kivilaan and Bandurski 1981).  Nearly 100% of seeds survived 30.5 months of burial in Sweden (Baskin et al. 2004). Seed survival is longer in undisturbed soil (Defelice 2001).  In a 5-year study, the number of seeds declined by an average of 43% per year in soil stirred four times each year and 24% per year in uncultivated soil (Mohler 2001, calculated from Roberts and Feast 1972).  Likewise, annual mortality was 35-52% in cultivated soil and 11-22% in undisturbed soil over 6 years in England (Roberts and Feast 1973).  Annual mortality rates of 19% in Alaska (Conn et al. 2006) and 21% in France (Gardarin et al. 2010) also have been reported for seeds in undisturbed soil.

Season of emergence:  Seedlings emerge in the fall and overwinter as rosettes close to the ground or emerge in the early spring (Baskin and Baskin 1989, Popay and Roberts 1970b, Werle et al. 2014).  When emerging is spring, it is among the earliest emerging species (Doll 2002).  A few seedlings also come up during the warmer parts of the growing season and are notably more common during relatively cool summers (Baskin and Baskin 1989).  In Michigan with relatively cool summers, shephard’s-purse emerged primarily in late summer and only a small fraction emerged in fall and spring (Hill et al. 2014).

Emergence depth:  Optimum emergence occurs approximately at the soil surface, most seedlings emerge from within the top 0.5” (1.3 cm) of soil, and very few emerge from deeper than 1” (2.5 cm) (Froud-Williams et al. 1984, Popay and Roberts 1970b). 

Photosynthetic pathway:  C3

Sensitivity to frost:  Shepherd’s-purse is very frost hardy, with acclimated plants surviving temperatures of 10 °F (-12 °C) with little damage (Cici and Van Acker 2011).  Individuals that germinate in the fall commonly persist through the winter.

Drought tolerance:  Shepherd's-purse is relatively drought tolerant.  For example, it grew better with alternating 4 days of watering and 10 days of drying than with regimes including more days of watering and fewer days of drying (Aksoy et al. 1998).

Mycorrhiza:  Most reports indicate the absence of mycorrhiza on this species in England (Harley and Harley 1987) and Utah (Pendleton and Smith 1983), but some samples from England had mycorrhizal infections (Harley and Harley 1987).

Response to fertility:  Shepherd’s-purse is most common on fertile soils.  Compared with many other weeds, however, it is only moderately responsive to balanced fertilization with N-P-K, but it does show a growth response to fertility rates beyond typical recommendations.  At low P, its growth increases linearly with N fertilization up to and probably beyond 133 lb N/A (150 kg N/ha) (Andreasen et al. 2006).  At low N, it increased slightly but linearly to increasing P up to 54 lb P/A (60 kg P/ha) (Andreasen et al. 2006).  The species prefers neutral soils but tolerates soil with a pH of 5 (Aksoy et al. 1998).

Soil physical requirements:  Shepherd’s-purse is common on a wide range of soil textures and drainage classes, but is intolerant of flooding.  It is highly tolerant of soil compaction.

Response to shade:  Shepherd’s-purse is relatively shade tolerant and will set seed in 80-92% shade (Aksoy et al.1998, Yasin et al. 2019).  It can grow at light levels similar to those at soil level in a grassland (Fenner 1978) or barley crop (Yasin et al. 2019) with a closed leaf canopy.

Sensitivity to disturbance:  Seedlings are tiny, fragile, and easily broken.  Even small rosettes readily retain soil on the root system, however, and will subsequently re-root after cultivation.  Plants survive and regrow well after one cutting at 2” (5 cm), but die after three cuts (Meiss et al. 2008).  The species is moderately tolerant of trampling (Aksoy et al. 1998).

Time from emergence to reproduction:  Flowering can occur in less than 4 weeks for spring emerging plants (Doll 2002).  Flowering time varies greatly both between and within populations (Neuffer and Hurka 1986).  Flowering varied from 6 to 16 weeks for the majority of European populations (Neuffer and Hurka 1986).  California populations showed a similar range with populations from hot, dry summer climates flowering earlier than those from cool, moist summer climates (Neuffer and Hurka 1999).  Time to first flowering ranged from 23 days for populations from Asia to 44 days for populations from Europe and early flowering was suggested as a mechanism for avoiding competition (Orsucci et al. 2019).  Flowering can be delayed up to 30 days by increasing levels of shade (Yasin et al. 2019).  Plants that begin flowering in early May begin producing ripe seeds by late May (Aksoy et al. 1998).

Pollination:  Shepherd’s-purse is primarily self-pollinated (Neuffer and Hurka 1986), but is also insect pollinated.

Reproduction:  Shepherd’s-purse reproduces only by seed.  The flowers open first at the base of the inflorescence and continue to form at the top even as the capsules lower on the plant mature and shed seeds (Aksoy 1998).  Consequently, an individual plant produces seeds for many weeks (Hurka and Haase 1982).  Seeds are viable when green fruit are full-sized (Gill 1938).  An average plant produces around 3,000 seeds but large plants may produce 30,000 to 60,000 seeds (Defelice 2001, Hurka and Haase 1982, Stevens 1932).  Immature capsules will continue to ripen and shed seeds even after the plant has been uprooted and killed.

Dispersal:  Because the seeds often reach high densities in soil, they are easily spread from one site to another in soil clinging to shoes, tillage machinery, and tires.  Seed dispersal is facilitated by the mucilaginous seed surface that allows them to cling to animals or machinery (Hurka and Haase 1982).  The seeds survive well in the digestive tracts of cows, sheep, horses, and deer (Myers et al. 2004) and manure is commonly contaminated with shepherd’s-purse seeds (Mt. Pleasant and Schlather 1994).  Germination is minimally affected by digestion and dispersal by earthworms (Hurka and Haase 1982), which can facilitate deep burial and long-term survival in soils.  Shepherd's-purse also can be dispersed in irrigation water (Kelley and Bruns 1975).

Common natural enemies:   Many species of insects attack shepherd's purse.  The aphids (Aphis euonymi) and (Myzus certus) cause leaf rolling.  Several curculio beetles in the genus Ceutorhynchus form galls on the leaves or stem.  The fly larvae Dasineura brassicae gall the shoots and Liriomyza strigara and Phytomyza horticola mine the leaves.  Shepherd's purse is acceptable to all mollusks on which it has been tested including the slug Agriolimax caruanae (Dirzo and Harper 1980).

Palatability:  Shepherd's-purse has lower protein and digestible matter than alfalfa (Temme et al. 1979).  The young foliage can be used as a pot herb or to provide a peppery taste in salads.  The seeds are edible, but are tiny and do not develop synchronously, which makes them hard to collect in quantity.  The plant has a wide variety of medicinal uses and these have contributed to its worldwide spread.  (Defelice 2001)

References:

• Aksoy, A., J. M. Dixon, and W. H. G. Hale.  1998.  Biological flora of the British Isles No. 199: Capsella bursa-pastoris (L.) Medikus (Thlaspi bursa-pastoris L., Bursa bursa-pastoris (L.) Shull, Bursa pastoris (L.) Weber).  Journal of Ecology 86:171-186.
• Andreasen, C., A.-S. Litz, and J. C. Streibig.  2006.  Growth response of six weed species and spring barley (Hordum vulgare) to increasing levels of nitrogen and phosphorus.  Weed Research 46:503-512.
• 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.
• Baskin, J. M., and C. C. Baskin.  1989.  Germination responses of buried seeds of Capsella bursa-pastoris exposed to seasonal temperature changes.  Weed Research 29:205-212.
• Cici, S. Z. H., and R. C. Van Acker.  2011.  Relative freezing tolerance of facultative winter annual weeds.  Canadian Journal of Plant Science 91:759-763.
• 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.
• Defelice, M. S.  2001.  Shepherd's-purse, Capsella bursa-pastoris (L.) Medic.  Weed Technology 15:892-895.
• Didon, U. M. E., A.-K. Kolseth, D. Widmark, and P. Persson.  2014.  Cover crop residues—effects on germination and early growth of annual weeds.  Weed Science 62:294-302.
• Dirzo, R., and J. L. Harper.  1980.  Experimental studies on slug-plant interactions: II. The effect of grazing by slugs on high density monocultures of Capsella bursa-pastoris and Poa annua.  Journal of Ecology 68:999-1011.
• Doisy, D., N. Colbach, J. Roger-Estrade, and S. Médiène.  2014.  Weed seed rain interception by grass cover depends on seed traits.  Weed Research 54:593-602.
• Doll, J.  2002.  Knowing when to look for what: Weed emergence and flowering sequences in Wisconsin.  https://extension.soils.wisc.edu/wp-content/uploads/sites/68/2016/07/Doll-2.pdf
• Fenner, M.  1978.  Susceptibility to shade in seedlings of colonizing and closed turf species.  New Phytologist 81:739-744.
• Froud-Williams, R. J., R. J. Chancellor, and D. S. H. Drennan.  1984.  The effects of seed burial and soil disturbance on emergence and survival of arable weeds in relation to minimal cultivation.  Journal of Applied Ecology 21:629-641.
• Gardarin, A., C. Dürr, M. R. Mannino, H. Busset, and N. Colbach.  2010.  Seed mortality in the soil is related to seed coat thickness.  Seed Science Research 20:243-256.
• Gill, N. T.  1938.  The viability of weed seeds at various stages of maturity.  Annals of Applied Biology 25:447-456.
• Harley, J. L., and E. L. Harley.  1987.  A check-list of mycorrhiza in the British flora.  New Phytologist 105:1-102.
• Hill, E. C., K. A. Renner, and C. L. Sprague.  2014.  Henbit (Lamium amplexicaule), common chickweed (Stellaria media), shepherd’s-purse (Capsella bursa-pastoris), and field pennycress (Thlaspi arvense): fecundity, seed dispersal, dormancy, and emergence.  Weed Science 62:97-106.
• Hurka, H., and R. Haase.  1982.  Seed ecology of Capsella bursa-pastoris (Cruciferae): dispersal mechanism and the soil seed bank.  Flora 172:35-46.
• Kelley, A. D., and V. F. Bruns.  1975.  Dissemination of weed seeds by irrigation water.  Weed Science 6:486-493.
• Kivilaan, A., and R. S. Bandurski.  1981.  The one-hundred-year period for Dr. Beal's seed viability experiment.  American Journal of Botany 68:1290-1292.
• Kumar, V., D. C. Brainard, and R. R. Bellinder.  2008.  Suppression of Powell amaranth (Amaranthus powellii), shepherd's-purse (Capsella bursa-pastoris), and corn chamomile (Anthemis arvensis) by buckwheat residues: role of nitrogen and fungal pathogens.  Weed Science 56:271-280.
• Lawley, Y. E., R. R. Weil, and J. R. Teasdale.  2011.  Forage radish cover crop suppresses winter annual weeds in fall and before corn planting.  Agronomy Journal 103:137-144.
• Meiss, H., N. Munier-Jolain, F. Henriot, and J. Caneill.  2008.  Effects of biomass, age and functional traits on regrowth of arable weeds after cutting.  Journal of Plant Diseases and Protection, Special Issue XXI:493-500.
• Mohler, C. L.  2001.  Weed life histories: identifying vulnerabilities.  In, Ecological Management of Agricultural Weeds, M. Liebman, C. L. Mohler, and C. P. Staver eds., pp.40-98.  Cambridge University Press: Cambridge, U.K.
• Mt. Pleasant, J., and K. J. Schlather.  1994.  Incidence of weed seed in cow (Bos sp.) manure and its importance as a weed source for cropland.  Weed Technology 8:304-310.
• Myers, J. A., M. Vellend, S. Gardescu, and P. L. Marks.  2004.  Seed dispersal by white-tailed deer: implications for long-distance dispersal, invasion, and migration of plants in eastern North America.  Oecologia 139:35-44.
• Neuffer, B., and H. Hurka.  1986.  Variation of development time until flowering in natural populations of Capsella bursa-pastoris (Cruciferae).  Plant Systematics and Evolution 152:277-296.
• Neuffer, B., and H. Hurka.  1988.  Germination behaviour in populations of Capsella bursa-pastoris (Cruciferae).  Plant Systematics and Evolution 161:35-47.
• Neuffer, B., and H. Hurka.  1999.  Colonization history and introduction dynamics of Capsella bursa-pastoris (Brassicaceae) in North America: isozymes and quantitative traits.  Molecular Ecology 8:1667-1681.
• Orsucci, M., P. Milesi, J. Hansen, J. Girodolle, S. Glémin, and M. Lascoux.  2019.  Ecological strategy and genetic load in the shepherd's purse (Capsella bursa-pastoris) from the core and the limit of its natural range.  https://www.biorxiv.org/content/biorxiv/early/2019/02/28/563569.full.pdf
• 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.
• Popay, A. I., and E. H. Roberts.  1970a.  Factors involved in the dormancy and germination of Capsella bursa-pastoris (L.) Medik. and Senecio vulgaris L.  Journal of Ecology 58:103-122.
• Popay, A. I., and E. H. Roberts.  1970b.  Ecology of Capsella bursa-pastoris (L.) Medik. and Senecio vulgaris L. in relation to germination behaviour.  Journal of Ecology 58:123-139.
• Roberts, H. A., and P. M. Feast.  1972.  Changes in the numbers of viable weed seeds in soil under different regimes.  Weed Research 13:298-303.
• Roberts, H. A., and P. M. Feast.  1973.  Emergence and longevity of seeds of annual weeds in cultivated and undisturbed soil.  Journal of Applied Ecology 10:133-143.
• Stevens, O. A.  1932.  The number and weight of seeds produced by weeds.  American Journal of Botany 19:784-794.
• Storkey, J., S. R. Moss, and J. W. Cussans.  2010.  Using assembly theory to explain changes in a weed flora response to agricultural intensification.  Weed Science 58:39-46.
• Temme, D. G., R. G. Harvey, R. S. Fawcett, and A. W. Young.  1979.  Effects of annual weed control on alfalfa forage quality.  Agronomy Journal 71:51-54.
• Terpstra, R.  1986.  Behavior of weed seed in soil clods.  Weed Science 34:889-895.
• USDA Plants.  USDA Agricultural Research Service Plants Data Base.  https://plants.usda.gov
• Werle, R., M. L. Bernards, T. J. Arkebauer, and J. L. Lindquist.  2014.  Environmental triggers of winter annual weed emergence in the midwestern United States.  Weed Science 62:83-96.
• Yasin, M., E. Rosenqvist, S. M. Jensen, and C. Andreasen.  2019.  The importance of reduced light intensity on the growth and development of six weed species.  Weed Research 59:130-144.