Wild radish

Images above: Left: Wild radish seedling (Antonio DiTommaso, Cornell University). Right: Wild radish young plant (Scott Morris, Cornell University).

Images above: Upper left: Wild radish flowering plant (Joseph DiTomaso, University of California, Davis). Upper right: Wild radish mature seed pods (Antonio DiTommaso, Cornell University). Bottom: Wild radish flower, yellow phase (Scott Morris, Cornell University).

Identification

Other common names:  charlock, jointed radish, wild turnip, jointed charlock, white charlock, wild kale, cadlock, runch, jointed wild radish

Family:  mustard family, Brassicaceae

Habit:  Winter or summer annual herb bolting from a rosette.

Description:  Seedling stems below cotyledons are purple and have stiff hairs.  Cotyledon blades are hairless, kidney-shaped to heart shaped, 0.4-0.8” (1-2 cm) long and slightly wider than long, and prominently veined.  Cotyledon stalks are 0.4-1” (1-2.5 cm) long and tapered.  First leaves are oval to oblong, alternate, long stalked and strongly veined with wavy, lobed and irregularly toothed edges.  The largest lobe occurs at the leaf tip, with 2-4 smaller lobes near the base.  Stiff, hairs are scattered on both leaf surfaces and on leaf edges.  Early leaves form a basal rosette.  Mature plants bolt from the rosette, producing a 1-4 ft (0.3-1.2 m) tall branched stem.  Stems are densely hairy at the base but more sparsely hairy toward the top.  Lower leaves are 2-8” (5-20 cm) long by 2” (5 cm) wide, oval to oblong, and long stalked.  Leaf edges are irregularly toothed and lobed like the young leaves.  Upper leaves are stalkless or short stalked, lance-shaped, less than 3” (7.5 cm) long.  Edges are entire to toothed, with 0-5 lobes at base.  All leaves have coarse, stiff hairs scattered on edges and on both surfaces.  The sturdy taproot has a strong radish scent.  Flowers occur in branched clusters at the ends of the stem and branches.  Individual flowers are 0.4-0.5” (1-1.3 cm) wide with 4 petals, and are pale yellow to cream-colored or white.  Petals usually have distinctive purple veins.  Purple-pink flowers have been observed and are speculated to be the result of introgression with cultivated radish (Cheam and Code 1995; Marie Simard, personal communication).  Flower stalks are upright and 0.25-1” (0.6-2.5 cm) long.  Seedpods form below the flowers and are initially cylindrical, green, and fleshy; they are 0.8-3” (1-7.5 cm) long with a 0.4-2” (1-5 cm) long beak and contain 2-10 seeds.  As seedpods ripen, they become brown and corky, ridged lengthwise, and constricted joints develop between the seeds.  Seed pods break into segments at the joints when seeds are mature; individual segments do not open.  Seeds are grooved, red-brown, 0.1-0.25” (0.25-0.6 cm) long by 0.06-0.1” (0.15-0.25 cm) wide, and kidney-shaped. 

Similar species:  Cultivated radish (Raphanus sativus L.) is very similar to wild radish, but has pink to purple flowers and unjointed seedpods with only 2-3 seeds.  Wild mustard (Sinapis arvensis L.) and other mustard species do not have purple-veined petals, and have seedpods that split when mature rather than break into segments.  Seeds are almost perfect spheres compared to wild radish seeds.  Wild radish leaves are hairier, rougher, and more lobed than wild mustard and the latter does not form a basal rosette.  Leaves of yellow rocket (Barbarea vulgaris W. T. Aiton) are glossy, dark green, and are not hairy like those of wild radish. 

Management

If wild radish is a problem, lime to pH 6.8 and avoid applying excess N.  Time applications of soluble N sources to correspond to periods of high crop uptake.   

In grain crops, use a tine weeder with stiff tines to break or bury as many wild radish plants as possible since the tap root and deep emergence makes seedlings resistant to uprooting.  Since the pods often do not shatter until wheat or canola harvest, consider using harvest weed seed control (HWSC) strategies for removing and destroying wild radish seeds.  This will greatly reduce seed return to the soil.  Wild radish genotypes have developed that flower early below harvesting height and potentially could evade seed harvesting strategies, but competition from a densely planted grain crop will offset this response and facilitate HWSC approaches (Sun et al. 2021).

In warm climates where wild radish acts as a winter annual, till very shallowly (1-2”) to stimulate germination and then till again to eliminate seedlings prior to planting grain crops.  A single cycle of tillage and incorporation is likely to be as effective as several (Cheam 1986).   In corn or soybeans, use a guidance system or belly mounted cultivator to get as close as possible to the row with shallow-pitched sweeps running close to the soil surface.  This will cut off the young wild radish with minimum damage to crop roots.  Hill up corn and soybeans before wild radish seedlings get too large for complete burial. 

In vegetable crops, use side-knives to get as close to the row as possible.  In-row weeding machines or hand hoeing will be necessary to obtain good control.  If soil is kept acidic for potato production, wild radish can pose a severe problem.  Mound about 2” of soil over the rows after planting potatoes; then tine weed aggressively when wild radish seedlings appear and, if necessary, repeat until the potato vines emerge.  The aggressive tine weeding will flatten out the field.  Hill potatoes in multiple operations to bury successive flushes of wild radish while they are still short.  Rather than mowing vines before harvest, use a forage harvester to blow the chopped plants and seed pods into a wagon for disposal.    

Where wild radish acts as a summer annual, use a short cultivated fallow in spring to reduce seed density before planting a late spring or summer crop.  Wild radish may not be very competitive in a summer crop, but this will reduce density in the next spring planted crop.  Where wild radish acts as a winter annual, use a late winter to very early spring cultivated fallow to flush seeds out of the soil before spring planted crops.  This will not help the spring crop because it will have few wild radish anyway, but the fallow will reduce wild radish density in later cool season crops.  Because wild radish has a persistent seed bank, suggestions for reducing seed density will likely require a few years to have a major impact.

If an exceptionally severe infestation of wild radish cannot be prevented from dropping seeds, let the seeds weather on the soil surface until the next crop.  Then moldboard plow deeply to 10” (25 cm).  In subsequent years, use direct drilling or shallower tillage of less than 6” (15 cm) to avoid bringing the remaining seeds to the surface (Cheam and Code 1995, Warwick and Francis 2005). 

Inspect grain seed for wild radish pod segments before sowing.  Pay particular attention to rye seed sold for use as a cover crop or forage that has not been certified for quality.

Ecology

Origin and distribution:  Wild radish is native to the Mediterranean regions of Europe, North Africa and the Middle East.  It has been introduced widely in Asia, Australia, Latin America and South Africa, and is a serious weed in grain growing parts of those regions (Warwick and Francis 2005).  It is generally rare or absent in the humid tropics.  It occurs widely in North America, but is rare or absent in much of the center of the continent.  As a weed, it causes the greatest problems in the Canadian Maritime Provinces, the Eastern Seaboard, and the Pacific coast (Warwick and Francis 2005).

Seed weight:  3.9-5.2 mg (Piskackova et al. 2020), 4.6-4.8 mg (Chauhan et al. 2006), 5.3-8.6 mg (Warwick and Francis 2005), 5.8-5.9 mg (Goggin et al. 2019), 8 mg (EFBI).  Seed weight within the same fruit can vary from 1.5 to 12 mg (Stanton 1984a), and seeds are heaviest in pods with few seeds (Stanton 1984b).  Seeds from early emerging cohorts are larger than seeds from later cohorts (Piskackova et al. 2020).  Larger seeds had the highest germination, growth, and reproductive output (Stanton 1984a,b).

Dormancy and germination:  Freshly produced wild radish seeds are usually dormant (Goggin et al. 2019, Malik et al. 2010, Mekenian and Willemsen 1975, Warwick and Francis 2005), although seeds from plants that emerge in fall are more dormant than those that emerge in spring (Cheam 1986).  Dormancy is caused both by a germination inhibitor in the seed coat and by physical restriction from the woody pod segment that usually remains attached to the seed (Cheam 1986, Mekenian and Willemsen 1975).  After-ripening for 6-months or burial in the soil over winter generally breaks dormancy (Mekenian and Willemsen 1975).  Exposure of seeds to high moisture and fluctuating temperatures appears to facilitate germination by breaking down the pod and seed coat (Mekenian and Willemsen 1975, Warwick and Francis 2005).  In some warm climate populations where the species behaves as a winter annual, exposure of seeds on the soil surface during the summer breaks dormancy (Cheam1986) and dormancy is lowest in fall, but progressively increases from winter to summer months (Malik et al. 2010).  In this case, cold stratification increases dormancy (Mekenian and Willemsen 1975).  Germination in fall is higher from buried seeds than from seeds on the soil surface (Malik et al. 2010).  Optimum temperature for wild radish germination is 39-68 °F (4-20 °C) (Kurth 1967, Malik et al. 2010) and improves with alternating temperatures within this range (Cheam and Code 1995, Malik et al. 2010).  Light has minimal effect on germination (Malik et al. 2010), and can be suppressive at low temperatures (Mekenian and Willemsen 1975).

Seed longevity:  Some wild radish seeds remain viable in soil for 15-20 years (Kurth 1967).  In a 5-year experiment in which the top 3” (7.5 cm) of soil was seeded and then stirred twice each year, the number of seeds declined by 29% per year (computed from Roberts and Boddrell 1983).  This was similar to the 33% annual decline in the seed bank during the first two years under a grass sod (Chancellor 1986).  In Australia, the number of viable seeds declined by 32% in one year when buried at 4” (10 cm) (Reeves et al. 1981).

Season of emergence:  In northern areas the species emerges primarily in the spring (Doll 2002).  In the southern parts of the U.S.A., seedlings can emerge all year, with peak emergence in fall and winter (Piskackova et al. 2020, Warwick and Francis 2005).  The base temperature for emergence is 40 °F (4.5 °C) (Piskackova et al. 2020).

Emergence depth:  Most seedlings emerge from the top 1.2” (3 cm) of soil but a few can emerge from as deep as 2.8” (7 cm) (Chancellor 1964).  Twice as many seedlings emerge from 0.4” (1 cm) as from the soil surface (Reeves et al. 1981).  When seeds were sown and tilled into the soil, average depth of seedling emergence was 1.1” (2.9 cm) with a range from 0.3-1.5” (0.8-3.9 cm) (Chauhan et al. 2006).

Photosynthetic pathway:  C3

Sensitivity to frost:  Seedlings are killed by sub-freezing temperatures, but young rosettes are frost hardy (Norsworthy et al. 2010) and the species commonly survives as a winter annual in the southern U.S.A.  Most seedlings that emerged in September in North Carolina survived to reproduce whereas seedlings that emerged in October or November did not (Piskackova et al. 2020).  Mature plants are killed by frost (Warwick and Francis 2005).

Drought tolerance:  The rarity of wild radish in the interior of North America is attributed to a lack of drought tolerance.  In California, moisture-deficit in the spring caused more adverse effects than moisture-deficit in the fall (Warwick and Francis 2005).

Mycorrhiza:  Wild radish is a poor mycorrhizal host (Cheam and Code 1995, Harley and Harley 1987), possibly because of anti-fungal compounds excreted from roots (Warwick and Francis 2005).

Response to fertility:  Wild radish is often associated with nitrogen rich soils.  In high N soils, wild radish will take up more N than it needs for growth, and stores it as nitrate.  If N is less available later in the life cycle, plants will use the previously stored nitrate to make proteins (Warwick and Francis 2005).  Nitrogen fertilizer increased vegetative growth, but not reproductive growth in a growth chamber experiment (Jablonski 1997).  Liming soil to increase the pH from 6.0 to 6.8 was a major factor contributing to decreased abundance of wild radish in an eleven-year study (Chancellor 1976).

Soil physical requirements:  Wild radish can occur on all soil types, including sand, clay, sandy loam, and chalky or saline soil, but it appears to do best on acidic sandy soils (Warwick and Francis 2005).

Response to shade:  Wild radish grows best in high light.  Late emerging plants bypass the rosette stage and bolt early (Madafiglio 1999).  Wild radish height and specific leaf area is greater under a wheat canopy than in the open, but overall biomass and potential seed production is reduced, especially for later emerging cohorts (Cousens et al. 2001).

Sensitivity to disturbance:  Cutting and grazing have minimal effect on wild radish seed production because of its ability to rapidly produce new flowering stems (Cheam and Code 1995).  Plants have a highly branched stem structure which favors recovery from cutting.  Also, multiple stems can form from buds at the base of rosette leaves when resources are adequate (Kelly et al. 2013).

Time from emergence to reproduction:  In Ontario, spring emerging wild radish begins flowering in 3 to 6 weeks, but seeds do not mature until August (Warwick and Francis 2005).  Plants emerging in Wisconsin took 7 weeks to mature (Doll 2002).  Plants mature most rapidly in warm weather (Cheam and Code 1995), and plants emerging in June in South Carolina required 44 days to mature whereas plants emerging in November required 231 days (Norsworthy et al. 2010).  In Western Australia, where the climate is similar to that of California, plants emerging in the fall took 90 days to flower and successively later emerging plants required shorter periods down to 49 days for plants emerging in the spring (Cheam 1986, Reeves et al. 1981).  In North Carolina, plants required a day length longer than 11 hours when in the late vegetative stage to flower (Piskackova et al. 2020).  Under rapid developmental conditions in Australia, viable seeds can form within pods 3 weeks after flowering (Madafiglio 1999).  The flowering period of wild radish in Quebec sufficiently overlaps that of canola for gene flow to potentially occur from herbicide-resistant canola to wild radish (Simard and Légère 2004). 

Pollination:  Wild radish cannot self-pollinate.  It is cross pollinated primarily by bees, butterflies, and syrphid flies (Cheam and Code 1995, Conner and Rush 1996, Warwick and Francis 2005).

Reproduction:  Plants produce from 5 to 10,000 seeds per plant, depending on region, competition, and the time of emergence (Warwick and Francis 2005, Norsworthy et al. 2010).  Plants in spring wheat in Quebec produced 50-150 seeds per plant, with early emerging individuals producing the most seeds.  In northern areas, plants continue to flower and produce seeds until killed by frost (Warwick and Francis 2005).  In South Carolina, fertilized, well watered plants grown with minimal competition produced 8,000-10,000 seeds when emerging in April, October or November, but less than 2,000 when emerging in June or July (Norsworthy et al. 2010).  Plants grown with wheat in Australia produced up to 1,000 seeds per plant (Reeves et al. 1981).  Most seeds are retained on the plant until grain harvest, however genotypes in Australia have the potential to flower 2 to 3 weeks earlier than common genotypes and set seeds below the cutting height of grain combines, thus evading potential seed collecting strategies at grain harvest (Sun et al. 2021).

Dispersal:  Seeds naturally disperse within 1 to 3 ft of the parent plant (Kelly et al. 2013).  Seeds may move greater distances in soil clinging to tires and machinery or in harvesting equipment (Kelly et al. 2013).  Pod segments are similar in size to cereal grain and are sometimes sown with seed grain (Cheam and Code 1995).  Plants are attractive to grazing mammals, and the seeds pass through to disperse in manure (Warwick and Francis 2005).

Common natural enemies:  Wild radish is eaten by grazing mammals and rodents (Warwick and Francis 2005).

Palatability:  Some people in the Mediterranean Region and Pakistan eat the leaves in salads or cooked.  Livestock find young plants palatable, but eating large quantities of wild radish (> 25% of the diet) can cause sickness.  The seeds are especially toxic (Cheam and Code 1995, Warwick and Francis 2005).

Note:  Green manure that included ground-up plants of wild radish suppressed emergence and growth of several crops and weeds in South Carolina (Warwick and Francis 2005, Norsworthy 2003).

References:

• Chancellor, R. J.  1964.  Depth of weed seed germination in the field.  Proceedings of the Seventh British Weed Control Conference, pp. 607-613.
• Chancellor, R. J.  1976.  Weed changes over 11 years in Wrenches, an arable field.  Proceedings 1976 British Crop Protection Conference—Weeds.  Volume 2:681-686.
• Chancellor, R. J.  1986.  Decline of arable weed seeds during 20 years in soil under grass and the periodicity of seedling emergence after cultivation.  Journal of Applied Ecology 23:631-637.
• Chauhan, B. S., G. Gill and C. Preston.  2006.  Seedling recruitment pattern and depth of recruitment of 10 weed species in minimum tillage and no-tillage seeding systems.  Weed Science 54:658-668.
• Cheam, A. H.  1986.  Seed production and seed dormancy in wild radish (Raphanus raphanistrum L.) and some possibilities for improving control.  Weed Research 26:405-413.
• Cheam, A. H., and G. R. Code.  1995.  The biology of Australian weeds. 24. Raphanus raphanistrum L.  Plant Protection Quarterly 10:2-13.
• Conner, J. K., and S. Rush.  1996.  Effects of flower size and number on pollinator visitation to wild radish, Raphanus raphanistrum.  Oecologia 105:509-516.
• Cousens, R. D., J. W. Warringa, J. E. Cameron, and V. Hoy.  2001.  Early growth and development of wild radish (Raphanus raphanistrum L.) in relation to wheat.  Australian Journal of Agricultural Research 52:755-769.
• Doll, J.  2002.  Knowing when to look for what: Weed emergence and flowering sequences in Wisconsin. Weed Science University of Wisconsin. https://extension.soils.wisc.edu/wp-content/uploads/sites/68/2016/07/Doll-2.pdf 
• EFBI.  Ecological Flora of the British Isles.  http://ecoflora.org.uk/ 
• Goggin, D. E., H. J. Beckie, C. Sayer, and S. B. Powles.  2019.  No auxinic herbicide-resistant cost in wild radish (Raphanus raphanistrum).  Weed Science 67:539-545.
• Harley, J. L., and E. L. Harley.  1987.  A check-list of mycorrhiza in the British flora.  New Phytologist 105:1-102.
• Jablonski, L. M.  1997.  Responses of vegetative and reproductive traits to elevated CO2 and nitrogen in Raphanus varieties.  Canadian Journal of Botany 75:533-545.
• Kelly, N., R. D. Cousens, M. S. Taghizadeh, J. S. Hanan, and D. Mouillot.  2013.  Plants as populations of release sites for seed dispersal: a structural-statistical analysis of the effects of competition on Raphanus raphanistrum.  Journal of Ecology 101:878-888.
• Kurth, H.  1967.  The germinative behaviour of seeds.  SYS Reporter 3:6-11.
• Madafiglio, G. P., R. W. Medd, and P. S. Cornish.  1999.  A decimal code for the growth and development stages of wild radish (Raphanus raphanistrum L.).  Plant Protection Quarterly 14:143-146.
• Malik, M. S., J. K. Norsworthy, M. B. Riley, and W. Bridges, Jr.  2010.  Temperature and light requirements for wild radish (Raphanus raphanistrum) germination over a 12-month period following maturation.  Weed Science 58:136-140.
• Mekenian, M. R., and R. W. Willemsen.  1975.  Germination characteristics of Raphanus raphanistrum. I. Laboratory studies.  Bulletin of the Torrey Botanical Club 102:243-252.
• Norsworthy, J. K.  2003.  Allelopathic potential of wild radish (Raphanus raphanistrum).  Weed Technology 17:307-313.
• Norsworthy, J. K., M. S. Malik, M. B. Riley, and W. Bridges, Jr.  2010.  Time of emergence affects survival and development of wild radish (Raphanus raphanistrum) in South Carolina.  Weed Science 58:402-407.
• Piskackova, T. R., S. C. Reberg-Horton, R. J. Richardson, K. M. Jennings, and R. G. Leon. 2020.  Incorporating environmental factors to describe wild radish (Raphanus raphanistrum) seedling emergence and plant phenology.  Weed Science 68:627–638.
• Reeves, T. G., G. R. Code, and C. M. Piggin.  1981.  Seed production and longevity, seasonal emergence, and phenology of wild radish, (Raphanus raphanistrum L.).  Australian Journal of Experimental Agriculture and Animal Husbandry 21:524-530.
• Roberts, H. A., and J. E. Boddrell.  1983.  Seed survival and periodicity of seedling emergence in eight species of Cruciferae.  Annals of Applied Biology 103:301-304.
• Simard, M.-J., and A. Légère.  2004.  Synchrony of flowering between canola and wild radish (Raphanus raphanistrum).  Weed Science 52:905-912.
• Stanton, M. L.  1984a.  Seed variation in wild radish: effect of seed size on components of seedling and adult fitness.  Ecology 65:1105-1112.
• Stanton, M. L.  1984b.  Developmental and genetic sources of seed weight variation in Raphanus raphanistrum L. (Brassicaceae).  American Journal of Botany 71:1090-1098.
• Sun, C., M. B. Ashworth, K. Flower, M. M. Vila-Aiub, R. L. Rocha, and H. J. Beckie.  2021.  The adaptive value of flowering time in wild radish (Raphanus raphanistrum).  Weed Science 69:203–209.
• Warwick, S. I., and A. Francis.  2005.  The biology of Canadian weeds. 132. Raphanus raphanistrum L.  Canadian Journal of Plant Science. 85: 709-733.