Lens-podded whitetop or Lens-podded hoarycress [Lepidium chalepense L.][CADDC][CalEPPC: B][CDFA list: B] Photographs
Map of Distribution
Hoary cress or Heart-podded
draba L.][CADDR][CalEPPC: A-2][CDFA
list: B] Photographs Map
Hairy whitetop or Globe-podded
hoarycress [Lepidium appelianum Al-Shehbaz][CADPU][CDFA
list: B] Photographs Map
to 0.4(0.5) m tall, with creeping horizontal roots that
vigorously produce new plants. Cardaria species
are problematic in natural areas and many crops, especially irrigated
crops such as alfalfa and sugar beets. Not until 1933 were 3 distinct
Cardaria species known to exist in North America. Consequently,
taxonomic references to Cardaria species in articles published
prior to 1933 are unclear. Although similar, each species differs
in chromosome number and herbicide resistance. All are self-incompatible.
Lens-podded (2n = 80) and hoary cress (2n = 62,
64) can hybridize, but only first generation hybrids survive under
natural conditions. Lens-podded and hairy whitetop were
introduced from Central Asia. Hoary cress (2n = 16) was
introduced from Eurasia.
roots to a depth of 25 cm and lateral roots with shoot buds within
1 month.Hoary cress: Cotyledons oval to elliptic, 7-9 mm
long, ~ 2.5 mm wide, unequal, pale gray-green, with peppery taste.
First leaves ovate to oblong, dull, scaly, somewhat larger than
the cotyledons, often with slightly wavy margins. Subsequent leaves
resemble first leaves, but sometimes have short fine hairs along
the margins. First and subsequent leaves have bases tapered
to petioles equal to or longer than the length of the blades.
No descriptions are available for lens-podded and hairy
whitetop. However, seedlings of these species likely resemble
those of hoary cress.
+/- erect, sparse to densely covered with simple short hairs.
Leaves alternate, gray-green, variable, obovate, (ob)lanceolate,
oblong to elliptic. Surfaces, especially lower, sparsely to densely
covered with simple, short white hairs. Margins irregularly
toothed to entire. Basal leaves short-stalked. Upper leaves sessile,
with rounded-acute- to acute-lobed bases that clasp the stem.
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and UNDERGROUND STRUCTURES:Plants develop extensive systems of persistent,
deep, vertical and horizontal roots that vigorously produce new
shoots at irregular intervals. Root fragments can generate
new plants. Vertical roots can penetrate the soil to depths
of 2 m or more. Roots can account for 75% of the total plant biomass
and, as a result, store considerable amounts of carbohydrates.
Carbohydrate reserves typically accumulate to maximum levels by
mid-summer and are minimal in early to mid-spring. Roots survive
cold winter climates and periods of drought. Mycorrhizal associations
do not develop.
often +/- flat-topped (compound corymbs). Flowers fragrant, numerous,
4-petaled, white. Insect-pollinated.
and SEEDS:Pods (silicles) 2-chambered, variable, inflated,
with a persistent style 1-2 mm long at the apex, do
not open (or open slowly) to release seeds. Seeds (0)1-2 per
chamber, ovoid, slightly flattened, reddish-brown,1.5-2 mm long,
1-1.5 mm wide, with minutely granular surfaces.
CHARACTERISTICS:Foliage dies back during extended periods of freezing
temperatures or drought.
sites, fields, grain and vegetable crops, especially irrigated
crops such as alfalfa and sugar beets, orchards, vineyards, roadsides,
ditches. Often grows on moderately moist, alkaline to saline soils,
but tolerates a wide range of soil types and moisture conditions.
DISTRIBUTION: All species are scattered throughout California
and uncommon in the desert regions.
vegetatively from creeping roots and
less importantly by seed. Root fragments generate new plants,
but regeneration is poor in dry soils. Under favorable conditions,
plants often increase vegetatively by more than a 61 cm (2 ft)
radius per year. Light stimulates seed germination but is not
required. Seed germinates in the fall after the first rains. Plants
typically do not flower the first year. One flowering stem of
lens-podded whitetop or hoary cress can produce
up to 850 mature pods. Lens-podded and hairy whitetop
(and probably hoary cress) compete poorly with shrubs in
FAVORING/DISCOURAGING SURVIVAL:Colonies are difficult to eliminate because of deep,
persistent roots. Cultivation can facilitate spread of plants
by dispersing root fragments. However, repeated cultivation (bimonthly
to monthly) can destroy colonies in 2-4 years. Flooding an area
with 15-25 cm of water for 2 months can eliminate troublesome
Cardaria species, perennial pepperweed [Lepidium
latifolium L.] has glabrous foliage, smaller pods (~
2 mm long) that are +/- flattened and not inflated, with
sessile stigmas less than 1 mm long at the apex, and stem
leaves that lack clasping lobed bases. In addition, perennial
pepperweed is typically taller (> 0.5 m), and its pods
open at maturity to release seed.
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Biology and prevention:
These Cardaria species are aggressive perennials native to southwest Asia.
They were likely introduced in multiple shipments of contaminated alfalfa
seed from Turkestan into North America over a period of 40-50 years. Cardaria
draba was first found in Yreka California in 1876, C. chalepensis was first
collected in Chino, California in 1918, and C. pubescens was first collected
in Alberta Canada and Michigan in 1919. All three species now occur primarily
throughout the Western United States, and are found throughout California.
They persist under a wide range of environmental conditions and are found
in irrigated croplands, roadsides, rangelands, and wildland areas. They are
also found in riparian-upland ecotones and are somewhat salt and alkaline
tolerant, but generally not shade tolerant. All three species readily establish
in disturbed areas in range and wildlands and are favored during years of
above average precipitation. Invasion potential is greater under heavily grazed
conditions or other disturbances. Infestations rapidly establish dense stands
and may exclude native species, reduce biodiversity and decrease rangeland
productivity and forage quality. In agricultural areas, they are most aggressive
in irrigated fields and in areas where cultivation is infrequent. They can
cause considerable yield losses in alfalfa, cereal crops, and orchards. Seed
production is important for establishment in new areas. Seed production is
greater in C. draba and C. chalepensis than C. pubescens. Seed viability may
be less than three years for C. draba, is likely longer for C. chalepensis
and is unknown for C. pubescens. Seed viability through animals is unknown.
However, seed do not persist for more than a month in manure. Seeds are dispersed
by water, vehicles, farm machinery, and contaminated hay and crop seeds. New
populations along roadsides and field edges and irrigation ditches should
be aggressively controlled to prevent seed spread to new areas. Plant only
certified seed to avoid spreading the problem to other fields. Although seed
production is somewhat important, the aggressive nature and stubborn persistence
of these weeds is due to an extensive system of vertical and lateral roots.
New shoots arise from buds on creeping laterals and may form many independent,
clonal plants if severed. Vertical roots may penetrate the soil to a depth
of 1.5-6 m, and allow the plant to withstand extensive drought. Approximately
75% of the total biomass of C. draba is belowground. C. chalepensis seems
to be more robust than the others to both mechanical injury and certain herbicides.
Mechanical: Mechanical control is extremely variable with these deeply-rooted
species. Rapid replenishment of depleted energy reserves in the roots is likely
for all three species. Therefore, any mechanical control must be aggressively
maintained for several years. Hoeing or hand pulling will require considerable
effort and may reduce other competitive species due to increased disturbance.
Infrequent tillage may also increase stem densities by severing rootstocks
that form numerous, independent plants. The extremely intensive tillage necessary
to eradicate these weeds may require repeated cultivation every 10 days during
the growing season for 2-5 years. Research from Australia has indicated repeated
cultivation even before new shoots emerge is critical. Mowing alone is generally
ineffective for control, as rapid regrowth occurs. However research on a similar
species, perennial pepperweed (Lepidium latifolium) has shown that mowing
followed by certain herbicides such as glyphosate has dramatically improved
control. The most effective timing for mowing is when plants are in the late
bud to early flowering stage. This will also reduce seed production, but may
also decrease competitive vegetation.
Biological: There are no biological control agents for use on these
species. Cattle and sheep will graze them; however, dairy animals grazing
Cardaria spp. may produce milk with objectionable taste and odor.
Fire: It is unlikely that prescribed burning will control Cardaria
spp. Numerous observations indicate that Cardaria spp. populations expand
following fire. This is likely due to emergence of new shoots from root buds
on lateral roots. In Australia, C. draba seedlings have been reported to rapidly
appear after grassland fires.
Chemical: Chemical control can be effective for all three species,
but must be maintained for several years to obtain long term control. Table
1 provides herbicide information for control of Cardaria spp. in California.
There are certain differences and problems that may arise with herbicide applications.
The most effective timing of application for all three species appears to
be in the bud to early flower stage. However, in California, the timing of
flowering is later for C. chalepensis than C. draba. Additionally, C. chalepensis
is very tolerant of 2,4-D compared to C. draba and C. pubescens. When these
species are growing together, herbicide applications may select for the species
not at the proper growth stage, and control will appear poor.
Table 1. Herbicides labeled for control of Cardaria spp.
Integrated management strategies: One of the prime areas for invasion
in irrigated crops is thinning stands of alfalfa. If possible, rotation to
a winter annual grain would increase early season competition and allow for
intensive cultivation and herbicide applications during the fallow season.
2,4-D and MCPA may also be used in cereals during the growing season, at rates
that will provide some Cardaria suppression. In heavily infested range and
wildland areas, mowing followed by an herbicide application to regrowth at
the bud stage may be the most effective treatment. Established perennial grasses
will provide additional suppression of Cardaria spp. However, heavy grazing
may reduce suppression. Where possible, shrub establishment may provide the
most effective long-term suppression. This is an intensive management process
that may be very difficult in heavily infested areas.
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