Blue mustard or Purple mustard [Chorispora tenella (Pallas) DC.][COBTE][CDFA list: B] Photographs Map of Distribution

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SYNONYMS:purple mustard, bead-podded mustard, tenella mustard, musk mustard

GENERAL DESCRIPTION:A competitive noxious winter annual with an unpleasant odor, to 0.5 m tall. Blue mustard infestations are problematic throughout the central U.S. and southern Canada. Infestations in grainfields can significantly reduce yields. Dairy cattle grazing on infested pastures can produce distasteful milk. Introduced from Russia and adjacent regions of Asia.

SEEDLINGS:Cotyledons lanceolate. Rosette leaves oblong to oblanceolate, typically sparsely covered with minute glandular hairs. Subsequent rosette leaf margins entire to wavy to pinnately lobed.

MATURE PLANT:Foliage sparsely to moderately covered with simple, minute glandular hairs that are sticky to touch. Stems leafy, branched mostly from the base. Leaves alternate, elliptic or oblong to lanceolate or oblanceolate. Lower stem leaves petioled, 3-8 cm long, with wavy-toothed to pinnately lobed margins. Upper stem leaves sessile, with entire to wavy-toothed margins.

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FLOWERS:Early spring. Showy. Petals 4, pale purple to bluish-purple, narrowly clawed, 10-13 mm long. Sepals 4, usually purple with narrow membranous margins, separate but form a tube, 6-8 mm long. Stamens 6 (4 long, 2 short), arrowhead-shaped.

FRUITS and SEEDS:Pods linear, +/- smooth, erect to spreading, typically curved upwards, nearly round in cross-section, with a beak 7-20 mm long at the apex, 30-45 mm long including beak, ~ 2-4 mm in diameter, slightly constricted between seeds at maturity. Pods break apart transversely into segments. Seeds reddish to brown, +/- spherical, ~ 1.5 mm in diameter, usually remain within the pod segment.


HABITAT:Dry disturbed sites, winter annual crops, especially winter wheat, roadsides, waste places. Tolerates a broad range of moisture, temperature, and soil conditions.

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DISTRIBUTION:Cascade Ranges, Central Valley, South Coast Ranges, South Coast, Great Basin. To 1300 m (4270 ft).

PROPAGATION/PHENOLOGY:Reproduces by seed. Germination occurs during the cool season, mostly after the first rains. Seedlings exist as basal rosettes until flowering stems are produced in early spring. Viable seed can be produced in as few as 10 days after flowers open.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Infestations can be difficult to control in grainfields because plants are somewhat tolerant to typical 2,4-D use rates. Rotation to spring planted crops produces additional control options, including cultivation or other registered herbicides.

SIMILAR SPECIES:Unlike blue mustard, radish [Raphanus sativus L] is typically sparsely covered with stiff non-glandular hairs and has pods that are grooved below. In addition, the introduced annual Malcolm stock [Malcolmia africana R.Br.][MAMAF] is densely covered with small branched, non-glandular hairs and has beakless pods that open longitudinally to release seeds. Malcolm stock occurs in dry disturbed areas and desert shrublands from the eastern Sierra Nevada to the Rocky Mountains. To 2000 m (6500 ft).


Prevention and control: Blue mustard is a winter annual native to Europe and was introduced to the United States in 1929, in contaminated grain seed. It is primarily a problem in winter annual cereal crops and may cause extensive yield losses at moderate infestations. Densities as low as 3 plants per square foot have reduced wheat yields by over 50%. Blue mustard may also infest roadsides, noncrop areas, and disturbed rangeland. Additionally, dairy animals grazing blue mustard produce milk with a bitter taste and foul odor. Blue mustard is still somewhat limited in its distribution in California and infestations frequently tend to spread along roads and field edges. Populations should be mapped and aggressively controlled to prevent the continued increase of this weed in cereals.
Blue mustard seeds are also frequently spread by contaminated seed and harvest equipment. Planting certified seed and cleaning equipment after working in infested areas help prevent its spread.

Mechanical: Cultivation is very effective for blue mustard control. However, mechanical control is generally limited in winter annual crops. The most effective way to reduce blue mustard infestations is to rotate to a spring-seeded crop. This allows for early spring tillage, which effectively controls blue mustard. Additionally, late spring emerging seedlings can also be controlled by in-crop cultivation and selected herbicides. This strategy will deplete the mustard seedbank over time. However, mustard seed may remain viable for several years.
Another alternative is to delay fall planting until after the initial flush of winter annual weeds. Tillage may then be used effectively for control. This strategy may be difficult to implement due to limited entry into wet fields.
Mowing will reduce, but not eliminate seed production. The optimal time for mowing is during the early flowering period, before viable seed are produced. Mowing should not be done after seed are produced, as this may increase dispersal. Small infestations may also be hand pulled. Most plants have a shallow taproot and can be removed without great difficulty.

Chemical: There are currently no reported cases of herbicide resistance in blue mustard. However, chlorsulfuron resistance has been detected in other members of the mustard family. The low labeled rates of 2,4-D amine are generally ineffective against blue mustard and may select for it by eliminating competition from other broadleaf weeds. Most herbicide treatments work best when blue mustard is in the rosette stage, and control is decreased after bolting occurs. Table 1 provides the basic herbicide information for chemical control of blue mustard in California. Always read the herbicide label for specific instructions before application.

Table 1. Chemical control of blue mustard in California
Herbicide Rate Comments
Chlorsulfuron 0.008-0.015 lb ai/A These herbicides are registered for use in small grains in California including wheat, barley and oats. Refer to herbicide labels for application timing, restrictions, and precautions.
Dicamba 0.06-0.12 lb ae/A  
Bromoxynil 0.25-0.38 lb ai/A  
2,4-D amine 0.5-0.87 lb ae/A  
MCPA amine 0.25-0.5 lb ae/A  
Paraquat 0.4-0.9 lb ai/A Glyphosate and paraquat are nonselective treatments for use in fallow and noncrop
Glyphosate 0.38-0.5 lb ae/A These rates of 2,4-D and dicamba are for fallow, noncrop, or rangeland treatments for broadleaf weed control
2,4-D amine 1-2 lb ae/A  
Dicamba 0.25-2.0 lb ae/A  
Chlorsulfuron 0.015-0.03 lb ai/A Noncrop treatment, with some selectivity in certain grasses
Sulfometuron 0.14-0.23 lb ai/A Noncrop, roadside treatment, with some selectivity in certain grasses

Integrated management strategies: In agricultural settings, an integrated strategy utilizing the following methods will be the most effective for blue mustard control. These practices are also important for general weed management of most winter annual weeds.
1) Use certified seed for planting winter annual crops.
2) Rotate to spring seeded crops to break the cycle of annual seed production
3) Rotate herbicides with different modes of action each year in continuous winter annual cropping systems

Butler, M. D. 1994. Blue mustard (Chorispora tenella (Pall.) DC). Pacific Northwest Cooperative Extension Publication No. 471.
Hickman, J. C. 1993. The Jepson Manual. Higher Plants of California. Berkeley, CA: University of California Press.
Wiese, A. F., Chenault, E. W., and Wood, M. L. 1986. Controlling weeds in wheat with chlorsulfuron. Proceedings, Southern Weed Science Society 39:101
William, R. D., Ball, D., Miller, T. L., Parker, R., Yenish, J. P., Callihan, R. H., Eberlein, C., Lee, G. A., and Morishita, DW. 1997. Pacific Northwest Weed Control Handbook. Corvallis, OR: Oregon State University.

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