Blue mustard or Purple
mustard [Chorispora tenella (Pallas) DC.][COBTE][CDFA list: B]
SYNONYMS:purple mustard, bead-podded mustard, tenella mustard, musk
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.
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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and UNDERGROUND STRUCTURES:Shallow taproot.
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.
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.
CHARACTERISTICS:No information available.
HABITAT:Dry disturbed sites, winter annual crops, especially winter
wheat, roadsides, waste places. Tolerates a broad range of moisture, temperature,
and soil conditions.
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.
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.
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.
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
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.
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
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