Wild mustard
Sinapis arvensis L. = Brassica kaber (DC.) L.C. Wheeler



Images above: Upper left: Wild mustard plant (Scott Morris, Cornell University). Upper right: Wild mustard seed pods (Scott Morris, Cornell University). Bottom: Wild mustard seedling (Antonio DiTommaso, Cornell University).
Identification
Other common names: charlock, field mustard, field kale, kedlock, common mustard, crunchweed, kraut-weed, water cress, yellow-flower, herrick, yellow mustard
Family: mustard family, Brassicaceae
Habit: Highly branched, summer annual herb.
Description: Seedlings have cotyledons that are kidney- or heart-shaped to round, 0.25-0.5” (0.6-1.3 cm) long by 0.25-0.75” (0.6-2 cm) wide. The cotyledons are hairless and have 0.4” (1 cm) long stalks. Young seedling leaves are alternate, egg- to club-shaped, and 0.4-0.8” (1-2 cm) long. Leaf edges are wavy with wide, irregular teeth. The upper surface of the leaves has scattered stiff hairs, a somewhat wrinkled appearance, and conspicuous sunken veins. Leaf stalks are 0.1-0.25” (0.25-0.6 cm) long and hairy. Early leaves form a basal rosette. Mature plants have hairy stems and are 16-40” (40-100 cm) tall. The stem hairs are stiff, sparse, point towards the base, and are denser lower on the stem. Leaves are alternate, hairy, 2-10” (5-25 cm) long by 0.5-2.75” (1.3-7 cm) wide, and larger towards the base of the plant. Lower leaves have long stalks, are oval- to egg-shaped, deeply lobed, and broadest at the tip. Upper leaves are smaller, lance-shaped, and have short stalks or are stalkless. The root system is a thin and branched taproot with many fibrous secondary roots. Clusters of yellow, 4-petaled flowers develop at branch tips on 0.1-0.3” (0.25-0.8 cm) long stalks. The flowers are 0.5-1.25” (1.3-3.2 cm) wide. Flowers and seedpods are often present simultaneously. Seedpods are upright, cylindrical, 1-1.75” (2.5-4.4 cm) long by 0.08-0.12” (0.2-0.3 cm) wide, with 0.2-0.3” (0.5-0.8 cm) long stalks and a tapering, 2- or 4-sided, flat tipped beak. The seeds are reddish brown or dark brown to black, round, and 0.06” (0.15 cm) wide.
Similar species: White mustard (Sinapis alba L.) has stalked upper leaves and hairy seedpods, while the upper leaves of wild mustard are often without stalks and the seedpods are hairless. Wild radish (Raphanus raphanistrum L.) has hairier, rougher leaves than those of wild mustard. Wild radish flowers have dark-veined petals, while the flowers of wild mustard lack distinct veins. Wild radish seedpods are larger than those of wild mustard; they appear “beaded” instead of entire or smooth, and break into segments rather than splitting open when ripe.
Management
This species establishes very quickly and consequently, it is among the hardest weeds to control with cultivation. If you expect wild mustard to be a problem based on past years, plant large seeded crops a little deeper than usual and blind cultivate aggressively before crop emergence. This practice will be most effective if the crop is planted near its optimum season for establishment. Frequent early cultivations will pay off, especially if your equipment will allow you to get close to the crop row. Throw soil into the crop row as soon as the crop will tolerate it to bury wild mustard seedlings.
Wild mustard reaches its peak emergence following tillage in early to mid-spring, particularly when tillage is preceded by fertilization with inorganic nitrogen. If an area is particularly thick with this species, consider rotating to a late planted crop, and use a spring cultivated fallow period to flush out and destroy part of the seed bank.
The growth rate and competitive ability of wild mustard increases greatly with increasing nitrogen fertility so if this weed is a problem, avoid over fertilizing with nitrogen rich inputs. Wild mustard grows best and is more competitive when nitrogen is side-dressed earlier rather than later (Paolini et al. 1999), so apply nitrogen as late after the crop is established as possible. This species is sensitive to shading so plant highly competitive crops in fields where this weed is abundant. High density plantings of cereal grains also are effective for suppressing this weed since it usually is shorter than the grain.
In cereal grains, most pods generally remain closed and seeds are retained on the plant until harvest (Mulligan and Bailey 1975). Consequently, weed seed collection during combining could substantially reduce population density (Burton et al. 2016, 2017).
Ecology
Origin and distribution: Wild mustard is native to temperate regions of Europe, Asia and North Africa. It has been introduced into North and South America, Australia and South Africa. It occurs throughout the agricultural regions of North America (Holm et al. 1997, Mulligan and Bailey 1975, Warwick et al. 2000).
Seed weight: Seed mass ranges from 1.0 to 2.3 mg (Lutman et al. 2002, Mennan and Ngouajio 2006, Paolini et al. 2001). Light brown colored seeds averaged 1.2 mg, whereas dark brown colored seeds averaged 1.5 mg (Paolini et al. 2001).
Dormancy and germination: Some seeds can germinate immediately following seed shed (21% in one experiment), but most freshly shed seeds are dormant with typically about 5% germination (Donald and Hoerauf 1985, Goudey et al. 1987, Luzuriaga et al. 2006, Mennan and Ngouajio 2006). Smaller plants with fewer fruit produced black seeds that had higher dormancy than red seeds produced on larger plants with more fruit (Luzuriaga et al. 2006). The higher mass and dormancy of dark compared to light colored seeds may be accounted for by the thicker seed coat of dark seeds (Paolini et al. 2001). Exposure to freezing temperatures over winter can relieve some dormancy, increasing germination from 5% to 28% (Donald and Hoerauf 1985). When buried deeply in soil, dormancy is induced in seeds (Benvenuti 2001), but burial over winter can increase germination and emergence if seeds are brought to the surface the following spring (Warwick et al. 2000). The degree of light sensitivity apparently varies between populations and environmental conditions, but generally germination is only weakly stimulated by exposure to light alone (Singh et al. 2022, Warwick et al. 2000). More germination is stimulated by a combination of exposure to light and inorganic nitrogen (Goudey et al. 1987, Warwick et al. 2000). Under these conditions, optimum temperatures for germination are 50-68 °F (10-20 °C), with daily alternating temperatures giving maximum response (Goudey et al. 1987). The optimum day/night temperature for germination of populations from Australia was 86/68 °F (30/20 °C) (Singh et al. 2022). In favorable conditions, seed germination occurs in 2 to 4 days, and emergence in the field occurs 5 to 7 days after initiation of germination (Mulligan and Bailey 1975).
Seed longevity: When left undisturbed, a few seeds can remain viable in the soil for 60 years, especially if they are deeply buried. However, mortality of seeds buried in packets in the surface 1” (2.5 cm) of soil was 22-45% per year (Donald 1993). Similarly, mortality of wild mustard seeds in tilled agricultural soils was 20-52% annually (Roberts and Boddrell 1983, Lutman et al. 2002).
Season of emergence: Wild mustard emerges primarily during the spring, beginning when soil temperature exceeds 40 °F (4 °C) and recent rainfall has occurred (Edwards 1980). It continues to emerge sporadically throughout the growing season with a secondary peak of emergence in the fall (Holm et al. 1997).
Emergence depth: Emergence is best from near the soil surface (Benvenuti et al 2001, Donald and Hoerauf 1985, Singh et al. 2022), is moderate from 2” (5 cm), and is negligible from 4” (10 cm) or deeper (Benvenuti et al 2001, Mennan and Ngouajio 2006, Singh et al. 2022).
Photosynthetic pathway: C3
Sensitivity to frost: Wild mustard can survive temperatures down to 18° F (-8° C) but suffers some damage (Cici and Van Acker 2011). Late germinating plants are commonly winter-killed before they can set seed (Mohler, personal observation).
Drought tolerance: Wild mustard has an exceptionally high density of stomates on the leaves (Mulligan and Bailey 1975), which facilitates rapid growth with optimum soil moisture, but could make it relatively drought sensitive under low soil moisture conditions. Wild mustard establishes an extensive root system. For example, the total length of all roots added together can reach 2.9 ft (87 cm) in length by the fifth day and 394 ft (12 m) by 21 days after emergence (Mulligan and Bailey 1975), which would facilitate water uptake during droughts. In one experiment, drought stress reduced plant height by 90% and seed production by 97% (Edwards 1980), but in another experiment, wild mustard plant height, seed production, seed dormancy, and competitive ability were only moderately decreased by drought (Wright et al. 1999).
Mycorrhiza: Wild mustard does not form symbiotic relationships with mycorrhizal fungi (Mulligan and Bailey 1975, Warwick et al. 2000).
Response to fertility: Wild mustard is highly responsive to N fertility, with plant size increasing in response to application rates up to 480 lb N/A (540 kg/ha) (Blackshaw et al. 2003). Increasing nitrogen fertility can enhance the competitiveness of wild mustard relative to selected crops (Liebman and Robichaux 1990), but barley can outcompete wild mustard even at high N application rates (Andreasen et al. 2006). Delaying N side-dressing from 28 to 56 days after emergence reduced wild mustard biomass and seed production by approximately 50% (Paolini et al. 1999). This species was highly responsive to P in one experiment (Hoveland et al. 1976) but was relatively unresponsive in two other experiments (Blackshaw et al. 2004, Andreasen et al. 2000). Plants grew twice as large on soil with high versus low K (Hoveland et al. 1976). Wild mustard plants have a high S content and may respond to S. Growth is reduced substantially at a pH of 4.7-4.8 compared to a pH of 5.7-6.5 (Buchanan et al. 1975).
Soil physical requirements: Wild mustard grows on a variety of soil types but it grows best and is most competitive on clay soils (Mulligan and Bailey 1975). Emergence is impaired in soils that dry and become crusted (Donald and Hoerauf 1985).
Response to shade: Shade reduces growth rate and seed production of wild mustard, while time to flowering lengthens (Steinger et al. 2003).
Sensitivity to disturbance: Because of the rapidly developing root system of wild mustard (Mulligan and Bailey 1975, see Drought tolerance section), plants very quickly become resistant to rotary hoeing or tine weeding so these operations should target the weed in the white thread stage. Small plants are susceptible to manual hoeing or cultivation, but plants nearing the flowering stage are prone to re-rooting in moist weather.
Time from emergence to reproduction: Wild mustard is a long-day plant that flowers and produces seed when daylength exceeds 16 hours (Huanga et al. 2001). In the northern parts of its range, wild mustard flowers 3-6 weeks after emergence, with late emerging plants flowering most quickly. Seeds mature 5-6 weeks later (Huanga et al. 2001, Shrestha and Swanton 2007, Mulligan and Bailey 1975). Time to flowering can be highly variable depending on drought and crop competition, both of which can delay flowering (Edwards 1980). In warmer parts of the U.S.A. fall emerging plants overwinter, flower in the spring and set seeds in early summer.
Pollination: Unlike most annual weeds, wild mustard is self-incompatible. Although it is an introduced species, plants are cross-pollinated by a wide variety of native insects (Mulligan and Bailey 1975). It provides nectar and pollen that attract beneficial insects that prey on crop pests (Warwick et al. 2000).
Reproduction: Plants in agricultural fields produce from 10-18 seeds per pod and 200 to 3,500 seeds per plant when competing with crops under normal moisture conditions (Blackshaw et al. 1987, Edwards 1980, Lutman 2002, Mulligan and Bailey 1975). Plants growing without competition are larger and produce more seeds (Mulligan and Bailey 1975). Reproduction is reduced substantially when plant density is low and plants are isolated from pollinator habitats (Steffan-Dewenter and Tscharntke 1999, Warwick et al. 2000). Wild mustard may die back during seed formation or it may continue to produce mature pods until frost depending on conditions, but seeds are generally not released until the plant is dead. In most trials in Saskatchewan fields, 98% of wild mustard seeds were retained at field pea, spring wheat, and canola harvests, suggesting that this species would be suitable for harvest weed seed control systems (Burton et al. 2016, 2017).
Dispersal: Since the pods are slow to open, wild mustard pods growing in grain fields are often collected and the seeds can be dispersed by combining and also can become contaminants in grain and forage seed (Mulligan and Bailey 1975, Warwick et al. 2000). Seeds are also dispersed in manure (Mt. Pleasant and Schlather 1994), and in soil clinging to shoes, tires and tillage machinery.
Common natural enemies: Wild mustard frequently shows substantial leaf damage from imported cabbageworm (Pieris rapae) and flea beatles (Phyllotreta soo). Despite substantial foliar and root damage from cabbageworms and wireworms, respectively, wild mustard plants can compensate and produce similar numbers and mass of seeds as plants without herbivory (Poveda et al. 2003).
Palatability: The young plants are palatable to livestock, and marginally palatable to humans when cooked (Mulligan and Bailey 1975). The seeds contain toxins, and animals should not be allowed to eat more than small amounts of maturing plants (Kingsbury 1964).
References:
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