Lepidium draba (hoary cress)

Pictures

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Picture	Title	Caption	Copyright
Title Vegetative stages Caption L. draba vegetative growth stages. Copyright Jamal R.S. Qasem	Vegetative stages	L. draba vegetative growth stages.	Jamal R.S. Qasem
Title L. draba growing among fruit trees Caption L. draba in fruit plantation (around trunk). Copyright Jamal R.S. Qasem	L. draba growing among fruit trees	L. draba in fruit plantation (around trunk).	Jamal R.S. Qasem
Title L. draba general view Caption L. draba in flower. Copyright Jamal R.S. Qasem	L. draba general view	L. draba in flower.	Jamal R.S. Qasem
Title L. draba in wheat field Caption L. draba in wheat field, showing allelopathic effects. Copyright Jamal R.S. Qasem	L. draba in wheat field	L. draba in wheat field, showing allelopathic effects.	Jamal R.S. Qasem

Identity

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Preferred Scientific Name

• Lepidium draba L. (1753)

Preferred Common Name

• hoary cress

Other Scientific Names

• Cardaria draba (L.) Desv.

International Common Names

• English: heart-podded hoary cress; perennial peppergrass; thanet cress; white top; white weed
• Spanish: capellans (Argentina); coclearia falsa (Argentina); descamisada (Argentina); lepidio; wancy (Argentina)
• Arabic: qinnaibrah
• Portuguese: erva fome

Local Common Names

• Canada: cranson dravier; perennial peppergrass
• Chile: cardaria
• Denmark: hjerteskulpet karse
• Egypt: lislis; nafal
• Finland: kynsimokrassi
• France: cranson dravier; lepidier; pain blanc; passerage; passerage drave
• Germany: Gemeine Pfeilkresse; Pfeilkresse; Stengelumfassende
• Iran: ozmak
• Iraq: hoary cress; jinnaibrah
• Italy: cocola
• Lebanon: kunaybrah
• Netherlands: pijlkruidkers
• Norway: honningkarse
• Saudi Arabia: gana barri; harf mashrigi; lislis; nafal
• South Africa: hoary cardaria; peperbos cardaria
• Spain: babol; berro; capellanes; falsa coclearia; floreta; mastuerzo; mastuerzo oriental; papolas
• Sweden: valsk krasse
• Turkey: cok senelik yabani tere; kir teresi

EPPO code

• CADDR (Cardaria draba)

Summary of Invasiveness

Top of page L. draba is found in a wide range of habitats ranging from roadsides (highly disturbed sites) to rangelands, meadows and pastures, cultivated fields, home gardens, national parks and wasteland. It exists at high and low latitudes, above and below sea level. It is found under irrigation and in soils of high moisture content and also exists in arid regions. It invades all soil types, although it prefers alkaline conditions and can germinate in saline soils. All of these characteristics and adaptations provide exceptional advantages for this noxious weed and reflect its high potential to invade different agricultural systems. The absence of L. draba plants from plantations or sites where it has not been reported may not be due to the species' ability to invade, survive, grow or develop in these sites but rather to the absence of initial infestation. The weed can invade both agricultural and natural ecosystems (Larson et al., 2000). In summary, L. draba is a serious threat to agriculture and the environment. It is of a high ecological tolerance and is potentially harmful to human and animal health. Its ability to invade and reproduce by different means and to host plant pathogenic agents make this weed invasive with significant problems to man and natural resources.

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Capparidales
•                         Family: Brassicaceae
•                             Genus: Lepidium
•                                 Species: Lepidium draba

Notes on Taxonomy and Nomenclature

Top of page Lepidium draba was previously considered to be in the genus Cardaria, but was placed into the genus Lepidium on the basis of recent molecular evidence which showed that all Cardaria species nested within Lepidium (Al-Shehbaz et al., 2002). Cardaria species have historically been placed in and out of Lepidium, but it appears that they have now found a stable phylogenetic and taxonomic position (http://www.sidney.ars.usda.gov/hoarycress/taxonomyandsys.html).

Two subspecies of L. draba are recognized: L. draba subsp. draba, previously known as Cardaria draba (heart-podded hoary cress); and L. draba subsp. chalepense, previously known as Cardaria chalepensis and C. draba var. repens (lens-podded hoary cress). Cardaria pubescens (globe-podded hoarycress) is now named Lepidium appelianum Al-Shehbaz as the name Lepidium pubescens is already in use for a different species in South America.

Description

Top of page L. draba is an annual or perennial herb (Zohary, 1966), sprouting and regenerating by adventitious buds on the extensive root system. It is often wrongly described as being rhizomatous, but it does not have true rhizomes in the sense of underground stems.

Stems are erect, subglabrous or grey-pubescent. Height approximately 10-50 cm, with a deep tap root or branched woody rootstock. Stems simple or branched above, covered with shallowly-toothed ovoid leaves clasping the stem with arrow-shaped bases, erect, arising from branching, woody stock. Basal leaves petioled, spatulate to narrowly-obovate, dentate-repand. The upper part of the stem branches into several many-flowered, long-stalked racemes of white flowers.

Leaves up to 10 x 4.5 cm, the radial ones more or less petiolate, spatulate or obovate-oblong, entire or dentate-repand, sometimes lyrately-lobed; stem leaves sessile, lanceolate to ovate with downward-pointed lobes at base, usually acute, dentate or entire, spreading to erect, oblong-lanceolate to broadly elliptical or ovate, sagittate-amplexicaul, acute or obtuse, entire or dentate.

The inflorescence is a dense flat-tapped corymbose panicle, terminal, pedicels 2-10 mm long (Zohary, 1966). Flowers are white and measure 3-4 mm. Sepals 1.5-2 x 1 mm, spreading, glabrous, scarious-white-margined. Petals twice as long as sepals, white; anthers yellow. Fruiting racemes elongated with pedicels 8-12 mm long; about 2-3 times as long as fruit, more or less horizontal ascending or spreading, teretefiliform. Fruits are pale brown, cordate-silicate, up to 5 mm, unwinged, transversely ovoid-cordate or heart-shaped, tipped by about 1 mm long persistent style and capitate stigma, sometimes one of the two cells rudimentary, valves reticulate, glabrescent, somewhat turgid, netted when dry, do not break open but break up into one-seeded portions which are then dispersed two-valved. Seeds solitary, ovoid, 2 mm long, 1.5 mm wide, slightly compressed, ellipsoidal, reddish-brown (Boulos, 1988).

Korsmo (1954) provides detailed anatomical information of this weed, and Delorit (1970) contains illustrations and photographs of its seed.

Plant Type

Top of page Annual
Broadleaved
Herbaceous
Perennial
Seed propagated
Vegetatively propagated

Distribution

Top of page L. draba has been reported in many Asian and European countries of moderate climate, and has also spread as a noxious weed in relatively cold regions of Canada and USA. In addition, it has been reported in several African countries, such as South Africa.

Although native to Mediterranean and western and central Asia, L. draba has become widely naturalized in many parts of the world, probably as a contaminant of seed supplies. It is one of the worst weeds in all European countries (Clay, 1987) and is also widespread in arid and semi-arid regions of certain parts of the world, such as Africa (Al-Ahmad, 1982; Qasem, 1995). This wide distribution reflects the phenotypic plasticity of the weed, its adaptability and ability to grow and proliferate under different environmental conditions.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/Region	Distribution	Last Reported	Origin	First Reported	Invasive	Reference	Notes
Asia
Afghanistan	Restricted distribution		Native		Invasive	Holm et al., 1991; EPPO, 2014
Iran	Restricted distribution		Native		Invasive	Boluri, 1977; Ghadiri, 1994; EPPO, 2014
Iraq	Restricted distribution		Native		Invasive	EPPO, 2014
Israel	Restricted distribution		Native		Invasive	EPPO, 2014
Jordan	Widespread		Native		Invasive	Qasem, 1995
Lebanon	Restricted distribution		Native		Invasive	Holm et al., 1991; EPPO, 2014
Pakistan	Present
Saudi Arabia	Widespread		Native		Invasive	Chaudhary et al., 1981
Syria	Widespread		Native		Invasive
Turkey	Restricted distribution		Native		Invasive	Holm et al., 1991; EPPO, 2014
Africa
Egypt	Widespread		Native		Invasive	El-Naggar, 1993
Morocco	Present					Mazih, 2015
South Africa	Restricted distribution				Invasive	Wells et al., 1986; Holm et al., 1991; EPPO, 2014
Tunisia	Widespread				Invasive	Holm et al., 1991
Zimbabwe	Present, few occurrences				Invasive	Holm et al., 1991
North America
Canada	Restricted distribution		Introduced		Invasive	Mulligan and Findlay, 1974; EPPO, 2014
Mexico	Widespread		Introduced		Invasive	Geronimo, 1978
USA	Widespread					EPPO, 2014
-Alaska	Present		Introduced			Lorenzi and Jeffery, 1987
-Arizona	Present		Introduced			Lorenzi and Jeffery, 1987
-Arkansas	Present		Introduced			Lorenzi and Jeffery, 1987
-California	Present		Introduced			Lorenzi and Jeffery, 1987
-Colorado	Present		Introduced			Lorenzi and Jeffery, 1987
-Connecticut	Present		Introduced			Lorenzi and Jeffery, 1987
-Delaware	Present		Introduced			Lorenzi and Jeffery, 1987
-Hawaii	Present		Introduced			Lorenzi and Jeffery, 1987
-Idaho	Present		Introduced			Lorenzi and Jeffery, 1987
-Illinois	Present		Introduced			Lorenzi and Jeffery, 1987
-Indiana	Present		Introduced			Lorenzi and Jeffery, 1987
-Iowa	Present		Introduced			Lorenzi and Jeffery, 1987
-Kansas	Present		Introduced			Lorenzi and Jeffery, 1987
-Kentucky	Present		Introduced			Lorenzi and Jeffery, 1987
-Maine	Present		Introduced			Lorenzi and Jeffery, 1987
-Maryland	Present		Introduced			Lorenzi and Jeffery, 1987
-Massachusetts	Present		Introduced			Lorenzi and Jeffery, 1987
-Michigan	Present		Introduced			Lorenzi and Jeffery, 1987
-Minnesota	Present		Introduced			Lorenzi and Jeffery, 1987
-Missouri	Present		Introduced			Lorenzi and Jeffery, 1987
-Montana	Widespread		Introduced		Invasive	Brattain and Fay, 1980; Lorenzi and Jeffery, 1987
-Nebraska	Present		Introduced			Lorenzi and Jeffery, 1987
-Nevada	Present		Introduced			Lorenzi and Jeffery, 1987
-New Hampshire	Present		Introduced			Lorenzi and Jeffery, 1987
-New Jersey	Present		Introduced			Lorenzi and Jeffery, 1987
-New Mexico	Present		Introduced			Lorenzi and Jeffery, 1987
-New York	Present		Introduced			Lorenzi and Jeffery, 1987
-North Dakota	Present		Introduced			Lorenzi and Jeffery, 1987
-Ohio	Present		Introduced			Lorenzi and Jeffery, 1987
-Oklahoma	Present		Introduced			Lorenzi and Jeffery, 1987
-Oregon	Widespread		Introduced		Invasive	Lorenzi and Jeffery, 1987; Miller et al., 1994; Larson et al., 2000
-Pennsylvania	Present		Introduced			Lorenzi and Jeffery, 1987
-Rhode Island	Present		Introduced			Lorenzi and Jeffery, 1987
-South Dakota	Present		Introduced			Lorenzi and Jeffery, 1987
-Texas	Present		Introduced			Lorenzi and Jeffery, 1987
-Utah	Present		Introduced			Lorenzi and Jeffery, 1987
-Vermont	Present		Introduced			Lorenzi and Jeffery, 1987
-Virginia	Present		Introduced			Lorenzi and Jeffery, 1987
-Washington	Widespread		Introduced		Invasive	Tamaki et al., 1982; Lorenzi and Jeffery, 1987
-West Virginia	Present		Introduced			Lorenzi and Jeffery, 1987
-Wisconsin	Present		Introduced			Lorenzi and Jeffery, 1987
-Wyoming	Present		Introduced			Lorenzi and Jeffery, 1987
Central America and Caribbean
Guatemala	Present, few occurrences				Invasive	Holm et al., 1991
South America
Argentina	Restricted distribution				Invasive	Rouquaud and Videla, 1996; EPPO, 2014
Chile	Present, few occurrences					Holm et al., 1991
Europe
Bulgaria	Widespread		Native		Invasive	Radev and Stefanov, 1974
Czech Republic	Absent, intercepted only		Native		Invasive	Stanzel, 1993
Czechoslovakia (former)	Widespread		Native		Invasive	Polak and Majkova, 1992
Former USSR	Widespread				Invasive	Holm et al., 1991
France	Widespread				Invasive	Pichot, 1991
Germany	Widespread				Invasive	Hetzel, 1985
Greece	Restricted distribution					EPPO, 2014
Hungary	Widespread				Invasive	Olah, 1979
Italy	Widespread				Invasive	Holm et al., 1991
Netherlands	Present, few occurrences					Holm et al., 1991
Poland	Widespread				Invasive	Lipa, 1983
Portugal	Restricted distribution					EPPO, 2014
Romania	Widespread				Invasive	Sarpe et al., 1989
Russian Federation	Restricted distribution					EPPO, 2014
Spain	Restricted distribution		Native		Invasive	Guil et al., 1997; EPPO, 2014
UK	Widespread		Native		Invasive	Morris, 1982
Yugoslavia (former)	Widespread				Invasive
Oceania
Australia	Widespread		Native		Invasive	Heap and Mitchell, 1992
-New South Wales	Present				Invasive	Lazarides et al., 1997
-South Australia	Present				Invasive	Lazarides et al., 1997
-Tasmania	Present, few occurrences				Invasive	Holm et al., 1991; Lazarides et al., 1997
-Victoria	Present				Invasive	Lazarides et al., 1997
-Western Australia	Present				Invasive	Lazarides et al., 1997
New Zealand	Present, few occurrences					Holm et al., 1991

History of Introduction and Spread

Top of page L. draba is native to the Mediterranean and western and central Asia including the Balkans, Georgia, Armenia, Azerbaijan, Irkutskaya Oblast, Turkey, Jordan, Syria, Iraq and Iran (http://www.nwcb.wa.gov/weed_info/hoarycress.html; http://www.fs.fed.us/database/feis/plants/forb/cardra/all.html). It has been widely introduced and naturalized throughout Europe and all other continents.

Seeds of L. draba were probably brought to the USA with contaminated lucerne seed. The weed is also thought to have been introduced as an impurity in mattress material in 1809 (http://www.co.steveday.clara.net/cress/guide.htm). It was first collected in California, USA, in 1876 (Groh, 1940). It has invaded over 100,000 ha in Oregon (Kiemnce and McInnis, 2002). It was first identified in Gallatin County, Montana, USA, in 1916 and has now invaded about 32,000 acres across the state (Elpel, 2000). It started to invade along the East Coast in the late 1990s, before gradually spreading to cover almost all parts of the continental USA except the south-east (Kiemnec and McInnis, 2002).

Habitat

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L. draba is a ruderal perennial weed (Simova-Tosic et al., 1996), widely reported from coastal, maritime and montane habitats. It is widespread on arable land, waste ground and roadsides (Morris, 1982; Qasem, 1993). Cropping systems such as limited tillage systems may favour its spread (Fernandez-Quintanilla et al., 1984) and it is especially vigorous under irrigation. It is found on a variety of loamy soils, from light to heavy, and prefers neutral to alkaline soils (Olah, 1979). It favours disturbed soils (turned and/or cultivated) with moderate moisture, especially roadsides, ditch banks, sub-irrigated pastures and rangeland (Elpel, 2000), or overgrazed and other areas where native plants face growth problems (http://mtwow.org/whitetop.html). It grows under open conditions, without shade, in different economically important crops and is found along roadsides. It is also reported in 6- to 9.6-year-old communities of saltcedar (Tamarix ramosissima) with 25% coverage (Brothrson et al., 1984) and occurs in Purshia tridentate/Festuca scabrella and Pseudoroegneria spicata habitats (Guenther et al., 1993). In other parts of the USA, it is associated with Artemesia tridentata ssp. tridentata and A. tridentata ssp. wyomingensis communities (McInnis et al., 1993). In Jordan, it is widely spread from the north of the country (1600 m above sea level; annual rainfall of 500-600 ml) to the drier regions of the centre and north-east, which receive less than 150-200 ml annual rainfall. Thick populations of low, vigorous plants, receiving the lowest annual rainfall, have been found close to the desert and sporadic plants or small patches have been recorded in lucerne in the Jordan Valley at 355 m below sea level (Qasem, unpublished data). L. draba has been observed at altitudes as high as 2100 m in the Alps and up to 1600 m in Iran (Holm et al., 1997); at 1700-2400 m in Baha plateau, Saudi Arabia; and at 200 m above sea level in Argentina (Conticello and Gandullo, 1991).

Habitat List

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Category	Habitat	Presence	Status
Littoral
	Coastal areas	Present, no further details
Terrestrial-managed
	Cultivated / agricultural land	Present, no further details	Harmful (pest or invasive)
	Disturbed areas	Present, no further details	Harmful (pest or invasive)
	Managed forests, plantations and orchards	Present, no further details	Harmful (pest or invasive)
	Managed grasslands (grazing systems)	Present, no further details	Harmful (pest or invasive)
	Protected agriculture (e.g. glasshouse production)	Present, no further details	Harmful (pest or invasive)
	Rail / roadsides	Present, no further details	Harmful (pest or invasive)
	Urban / peri-urban areas	Present, no further details	Harmful (pest or invasive)
Terrestrial-natural/semi-natural
	Deserts	Present, no further details	Harmful (pest or invasive)
	High altitudes, uplands	Present, no further details	Harmful (pest or invasive)
	Natural forests	Present, no further details	Harmful (pest or invasive)
	Natural grasslands	Present, no further details	Harmful (pest or invasive)
	Riverbanks	Present, no further details	Harmful (pest or invasive)
	Wetlands	Present, no further details	Harmful (pest or invasive)

Hosts/Species Affected

Top of page Although L. draba has been reported in more than 38 countries, only a limited number of host crops have been mentioned. As it is a perennial weed, it prefers non- or less-disturbed habitats and thus is commonly found as a weed of fruit trees and rangelands. However, it also has a strong ability to invade field crops and to cause great yield losses through competition or allelopathy, or both.

Host Plants and Other Plants Affected

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Plant name	Family	Context
Avena sativa (oats)	Poaceae	Main
Beta vulgaris var. saccharifera (sugarbeet)	Chenopodiaceae	Main
Citrus	Rutaceae	Main
Crocus sativus (saffron)	Iridaceae	Main
Fragaria ananassa (strawberry)	Rosaceae	Other
fruit trees		Main
Gossypium hirsutum (Bourbon cotton)	Malvaceae	Other
Helianthus annuus (sunflower)	Asteraceae	Main
Hordeum vulgare (barley)	Poaceae	Main
Lens culinaris subsp. culinaris (lentil)	Fabaceae	Other
Malus domestica (apple)	Rosaceae	Main
Medicago sativa (lucerne)	Fabaceae	Main
Nicotiana tabacum (tobacco)	Solanaceae	Main
pastures		Main
Pistacia vera (pistachio)	Anacardiaceae	Main
Pyrus communis (European pear)	Rosaceae	Main
Secale cereale (rye)	Poaceae	Other
Solanum tuberosum (potato)	Solanaceae	Main
Triticum aestivum (wheat)	Poaceae	Main
Triticum turgidum (durum wheat)	Poaceae	Main
Vitis vinifera (grapevine)	Vitaceae	Main
Zea mays (maize)	Poaceae	Main

Growth Stages

Top of page Flowering stage, Post-harvest, Pre-emergence, Seedling stage, Vegetative growing stage

Biology and Ecology

Top of page Genetics

L. draba is self-incompatible and is pollinated by insects (Lacey and Lacey, 1985).

Physiology and Phenology

L. draba produces large amounts of seed, some 2300 seeds per stem or 1200-4800 seeds per plant have beed recorded (Elpel, 2000). In temperate zones such as Canada, the flowering period is from May to July, with mature seed produced 1 month later. The minimum temperature for germination reported by Brown and Porter (1942) was 0.5°C, the maximum was 40°C, and the optimum was between 20 and 30°C. Light was not required for germination but enhanced germination rates, whereas oxygen levels below 10% and above 55% were unfavourable to germination. Seeds buried at a depth of 10-15 cm for 3 years rapidly decreased in viability; however, they were reported to retain viability in the soil for about 2 years (Elpel, 2000). Kiemnec and Larson (1991) observed that germination of L. draba decreased with lower osmotic potential. Increases in salinity up to an electrical conductivity (EC) of 12 ds/m had no effect on germination, but root growth was reduced by decreases in osmotic potential.

L. draba perennates by rootstocks that have abundant resources, and can overwinter and produce vigorous new shoots in the spring. Miller et al. (1994) reported similar phenology of the weed in different locations, despite differences in drought occurrence between the study sites. They reported 13C translocation to below-ground tissues occurring within 1 hour of labelling, which reached a peak within 24 hours. However, the greatest enrichment of roots occurred during the flowering stage. The peak in below-ground carbon allocation occurred at a stage when leaf conductance was declining rapidly. The same authors concluded that the short period of maximum carbon allocation below ground, the large proportion of subterranean tissue, and the wide variation of phenology among plants at a given time may account for the difficulty in chemically controlling L. draba.

Neururer (1986) concluded that undiversified rotations, minimal tillage, chemical selection and inappropriate control timing within a rotation are factors that have contributed to an increasing proliferation of perennial weeds in sugarbeet, including L. draba. The weed competes highly for soil moisture in arid regions, and its growth increases with increasing water consumption (Al-Ahmad, 1982).

Reproductive Biology

L. draba reproduces by seeds, root stock, and creeping roots or rhizomes (http:mtwow.org/whitetop.html). It can spread vegetatively at a rate of 2 m/year (Prach, 1988); a single plant can spread over an area of 3.6 m in diameter in 1 year (Miller, 1986) and fragments can give rise to new shoots throughout the season (Miller et al., 1994). The majority (approximately 76%) of the weed biomass is located below the ground and the deeply penetrating, creeping roots make it difficult to eradicate. If the weed is left unchecked, it soon colonizes large areas, choking the other plants present.

Branching patterns generally start with development of the first roots from the radicle in the initial 2-3 weeks of growth; first-order lateral roots grow outwards and then downwards to become vertical roots. Secondary lateral roots and shoot buds usually develop just below where the lateral roots turn downwards. Buds at or below the soil surface may become subterranean roots that are able to produce shoot buds later, whereas buds higher up the plant become rosettes. New crowns form rapidly from adventitious buds on upper roots if the crown is damaged. In this way, dense colonies of the weed can easily exclude other vegetation (Holm et al., 1997).

Air Temperature

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Parameter	Lower limit	Upper limit
Mean annual temperature (ºC)	1	40
Mean maximum temperature of hottest month (ºC)	25	36
Mean minimum temperature of coldest month (ºC)	10	15

Rainfall

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Parameter	Lower limit	Upper limit	Description
Dry season duration	4	5	number of consecutive months with <40 mm rainfall
Mean annual rainfall	150	700	mm; lower/upper limits

Rainfall Regime

Top of page Winter

Soil Tolerances

Top of page

Soil drainage

• free

Soil reaction

• alkaline
• neutral

Soil texture

• heavy
• light
• medium

Special soil tolerances

• infertile
• saline
• shallow

Natural enemies

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Natural enemy	Type	Life stages	Specificity	References	Biological control in	Biological control on
Aceria drabae	Herbivore	Inflorescence/Seeds
Ceutorhynchus turbatus	Herbivore	Stems
Phoma macrostoma	Pathogen			Caesar et al., 2012

Notes on Natural Enemies

Top of page L. draba is a host of Beet western yellows virus and Tobacco mosaic virus, and is attacked by different species of insects and mites. These viruses are economically important and can cause severe crop losses. Only one or two of the herbivores reported are host specific, whereas the rest, such as Pieris brassicae (Mushtaque and Mohyuddin, 1984), can attack many other plant species including some important crops. L. draba can therefore serve as an alternative host for all of these agricultural pests, except Aceria drabae, which is monophagous and therefore highly recommended for biological control of this noxious weed, and probably the shoot-eating beetle, Ceutorhynchus turbatus.

Means of Movement and Dispersal

Top of page Natural dispersal (non-biotic)

L. draba is a very difficult weed to control because its roots penetrate deep into the soil, store food reserves and can regenerate quickly after being fragmented during tillage. Irrigation facilitates the dispersal and invasion of L. draba by transporting root material from neglected ditch banks (Mulligan and Findlay, 1974). Wind currents may play a role in its seed or root dissemination.

Vector transmission

L. draba produces large numbers of seeds which can pass through the digestive tract of livestock unharmed, and which are also difficult to separate from crop seeds of similar size, such as lucerne.

Agricultural practices

Seeds or fragments can be mechanically transmitted from infested to clean areas through seed-contaminated agricultural machines and other vehicles which pass through the patches of this weed in roadsides, waste areas, national parks or range lands (http://mtwow.org/whitetop.html). Tillage is an important practice responsible on transmitting root segments from infested to clean fields (www.nwcb.wa.gov/weed_info/hoarycress.html).

Accidental introduction

Packed agricultural materials contaminated with seeds or root fragments of L. draba is another possible means of introduction (http://mtwow.org/whitetop.html) and contaminated crop seeds such as lucerne may have a significant role in its introduction or dispersal (Elpel, 2000).

Intentional introduction

L. draba may be introduced intentionally to new regions in the world either as seeds for human consumption in the form of flavouring agent or food additives (http://www.fs.fed.us/database/feis/plants/forb/cardra/aa.html) or as an ornamental plant for use in home or public gardens, or national parks. The whole plant may be introduced as a green vegetable to certain parts of the world because of its high nutritional value (Guil et al., 1997).

Pathway Vectors

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Vector	Notes	Long Distance	Local	References
Containers and packaging - wood		Yes
Land vehicles	All including agricultural machines, undercarriage	Yes
Plants or parts of plants	Mattress materials	Yes
Soil, sand and gravel		Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transport	Pest stages	Borne internally	Borne externally	Visibility of pest or symptoms
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx	flowers
Roots	roots
Stems (above ground)/Shoots/Trunks/Branches	stems
True seeds (inc. grain)	seeds

Plant parts not known to carry the pest in trade/transport
Growing medium accompanying plants
Leaves

Impact Summary

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Category	Impact
Animal/plant collections	Negative
Animal/plant products	Negative
Biodiversity (generally)	Negative
Crop production	Negative
Environment (generally)	Negative
Fisheries / aquaculture	None
Forestry production	Negative
Human health	Negative
Livestock production	Negative
Native fauna	None
Native flora	Negative
Rare/protected species	Negative
Tourism	Negative
Trade/international relations	Negative
Transport/travel	Negative

Impact

Top of page L. draba is a serious weed of maize, cereals, potatoes, sugarbeet, sunflower, tobacco, vegetables and vineyards in Europe. It is a principal weed of barley in the former Soviet Union, cereals in Australia and Jordan, orchards in Jordan, Spain and Switzerland, sugarbeet in Iran, and pastures and rangelands of South Africa and USA. It is also a common weed of barley in Canada and Greece; cereals in Iran, Tunisia and Turkey; citrus in Australia; lucerne in the Czech Republic; oats in Canada and Greece; rye in Greece; and vineyards in Iran, Greece and Turkey (Holm et al., 1997). It has the potential to reduce the value of high-value wheat lands in the USA (http://www.nwcb.wa.gov/weed_info/hoarycress.html), is host to various agricultural pests and serves as a reservoir host for different viruses including sugarbeet and rape infection by Beet western yellows virus in former Czechoslovakia (Polak and Majkova, 1992).

Although L. draba can be found growing under different cropping systems of field crops and orchards, its toxicity and unpalatability to cattle make it difficult to control through grazing. The limited number of possible biocontrol agents effectively attacking this species, its phenotypic plasticity and geographical tolerance also contribute to its significant success as an agricultural pest.

Environmental Impact

Top of page L. draba has been reported as a weed of high allelopathic activity against different crop species, including many wheat and barley cultivars (Qasem, 1993a, b, 1994, 1995), several vegetable crops (Obaid, 1996; Qasem, 2001; Obaid and Qasem, 2002) and wheat, lucerne, crested wheatgrass, bluebunch wheatgrass and hoary cress (Kiemnec and McInnis, 2002). Shoot and root extracts, water leachates and dried residues of L. draba added to the soil all inhibited germination, growth and development of different crop species. L. draba has been known to replace fields of lucerne if left uncontrolled (Mulligan and Findlay, 1974; Pacific Northwest Extention Service, 1974). Seedlings are capable of extracting significant amounts of moisture from the soil and Brattain and Fay (1980) observed that for each 2-week delay in controlling L. draba, loss of soil moisture increased substantially. It increases soil erosion and decreases desirable plants and pushes out the native plants (http://mtwow.org/whitetop.html).

Impact: Biodiversity

Top of page L. draba invades rangelands and arid regions in different parts of the world. It is self-incompatible and pollinated by insects (Lacey and Lacey, 1985). It is a very aggressive weed species, which competes strongly with native plants and can eventually eliminate desirable plants completely (http://www.colostate.edu/Depts/CoopExt/TRA/whtop.html).

Threatened Species

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Threatened Species	Conservation Status	Where Threatened	Mechanism	References	Notes
Grindelia fraxinipratensis (ash meadows gumplant)	NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened species	California; Nevada	Competition - monopolizing resources	US Fish and Wildlife Service, 2007a
Holocarpha macradenia (Santa Cruz tarplant)	NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened species	California	Competition - monopolizing resources; Ecosystem change / habitat alteration	US Fish and Wildlife Service, 2014
Silene spaldingii (Spalding's catchfly)	USA ESA listing as threatened species USA ESA listing as threatened species	Idaho; Montana; Oregon; Washington	Competition - monopolizing resources	US Fish and Wildlife Service, 2007b
Thysanocarpus conchuliferus (Santa Cruz Island fringepod)	USA ESA listing as endangered species USA ESA listing as endangered species	California	Competition - monopolizing resources	US Fish and Wildlife Service, 2009b
Zeltnera namophila	No Details	California; Nevada	Competition - monopolizing resources	US Fish and Wildlife Service, 2009a

Social Impact

Top of page L. draba is a perennial weed which is difficult to control. Control methods therefore add appreciably to the cost of farm operations. The abundance and spread of L. draba as a ruderal and segetal weed species creates other problems in outcompeting useful plants and causing a potential fire hazard. Its allelopathic activity impacts negatively on the environment and species biodiversity, and its toxic properties impose hazards to humans and animal welfare. In general, the widespread growth habit of the weed, tolerance to environmental conditions and high regenerative potential by seeds and rhizomes make L. draba a significant threat to humans and their activities. L. draba has been reported as one of the exotic weed species invading Yellowstone National Park, USA, causing substantial impact on the park's natural and cultural resources and receiving a high management priority (Olliff et al., 2001).

Risk and Impact Factors

Top of page Invasiveness

• Invasive in its native range
• Proved invasive outside its native range
• Highly adaptable to different environments
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Highly mobile locally
• Has high reproductive potential
• Has propagules that can remain viable for more than one year

Impact outcomes

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Negatively impacts agriculture
• Negatively impacts human health
• Negatively impacts animal health
• Negatively impacts tourism
• Reduced amenity values
• Reduced native biodiversity

Impact mechanisms

• Competition - monopolizing resources
• Pest and disease transmission

Likelihood of entry/control

• Highly likely to be transported internationally accidentally
• Highly likely to be transported internationally deliberately
• Difficult to identify/detect as a commodity contaminant
• Difficult/costly to control

Uses

Top of page L. draba has been reported as an edible wild species in Spain, with a crude protein content higher than leaves of spinach and cabbage (Guil-Guerrero et al., 1997). Crude protein levels between 7.7 and 28.8% have been reported (Szabo et al., 1974; McInnis et al., 1993), with the stems containing more protein than the leaves. L. draba is reported to contain 1.23% of erucic acid (Guil et al., 1997). At one time, the seeds of L. draba were ground and used as a substitute for pepper (Mulligan and Findlay, 1974) and the whole plant collected in certain parts of the world and cooked for human consumption. The flowers of L. draba serve as pollen and nectar sources for many insects (http://www.nwcb.wa.gov/weed_info/hoarycress.html).

McInnis et al. (1993) reported L. draba to be unpalatable to livestock and to contain potentially toxic glucosinolates, although sheep consumed it during the early growth stages and cattle ingested large quantities of seed heads. As sulfur levels can range from 0.73 to 2.69% and high levels of this element are probably due to the presence of glucosinolates and their hydrolysis products, sheep and cattle grazing in weed-infested rangelands should be given supplemental iodine. Mature and non-lactating animals should be utilized or access to the plant restricted because, if sufficient amounts are ingested, milk flavour can be affected.

Dornberger and Lich (1982) reported that extracts from aerial parts of L. draba had cytotoxic activity and interfered with the nucleic acid metabolism of bacteria during screening for antimicrobial substances.

Uses List

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Human food and beverage

• Spices and culinary herbs
• Vegetable

Similarities to Other Species/Conditions

Top of page L. draba subsp. draba has been previously confused with the other hoary cresses, L. draba subsp. chalepense (formerly Cardaria chalepensis and C. draba var. repens) and L. appelianum (formerly Cardaria pubescens) in North America. These are primarily weeds of arable land.

Distinctions between the hoary cresses are based on a few fruit characters: L. draba subsp. draba has a fruit shaped like an inverted heart, with a persistent style, hairless and deflating at maturity, usually containing two seeds; in L. draba subsp. chalepense, the fruit is oval- to lens-shaped, has a slightly longer style than in subsp. draba, and it stays inflated at maturity, usually containing four seeds; the fruit of L. appelianum is globose, hairy and remains inflated when mature, usually containing four seeds.

Lepidium sativum, L. latifolium, L. spinescens, L. spinosum and L. aucheri have a racemose inflorescence, simple or paniculate, and ebracteate. Their petals are equal, longer or sometimes shorter than sepals, or extremely reduced. L. draba and L. appelianum have corymbose, flowering racemes, whereas L. draba subsp. draba has white petals twice as long as the sepals and its leaves are not clasping.

Prevention and Control

Top of page Cultural Control

Soil cultivation can prevent reproduction of L. draba by creeping roots (Lipa, 1983), whereas direct drilling of cereals encourages growth (Fernandez-Quintanilla et al., 1984). Rouquand and Videla (1996) found that a combination of hoeing and glyphosate or weed removal when above-ground biomass was at a maximum in August and September, followed by glyphosate application in February, was the most effective strategy for control of L. draba. In Canada, L. draba was eliminated in 3 years following intensive tillage (24 operations at 2-week intervals) with disc or sub-surface cultivators (Holm et al., 1997). The seeds were killed after being buried in moist compacted manure for 1 month (http://www.nwcb.wa.gov/weed_info/hoarycress.html). Early spring blowing and planting to a cereal crops can control L. draba (Mulligan and Findlay, 1974) and out-compete the weed through dense stands of perennial grasses and legumes such as lucerne (Elpel, 2000). Grazing by sheep and goats is effective when the weed is the most abundant food source, or at the bud stage. Cattle eat L. draba more in the spring and grazing may be effective, but only at early growth or seed pod stages. Although the weed is nutritious, it is generally unpalatable and not attractive when other sources of food are available. In addition, it can cause a lot of health complications to grazing animals due to its content of glucosinolate glycosides. In general, the best management of L. draba is probably through a combination of competitive crops, tillage and herbicides.

Mechanical Control

Mechanical control seems an ineffective method of control because hand-weeding is impractical for perennial weed control, where weeds regenerate from below-ground vegetative parts. The weed must be tall enough to pull out from the soil, but hidden rhizomes or creeping roots below the soil surface can re-establish the weed. Mowing with a lawn mower or weed whacker can reduce the competitive ability of the weed and its ability to produce seeds if practised on time, but it is confined to small area and is ineffective against buried seeds and creeping roots or rhizomes. Cultivation may be a time- and energy-consuming method of control for perennial weed infestation unless it is repeated many times at the proper time and under the proper conditions, short intervals and during re-budding stage of L. draba, but may also enhance rhizome dissemination and increase infestation in wet soil.

Chemical Control

The herbicide 2,4-D has been widely used for control, but must be applied for 3 years or more at the early bud stage before flowering or in the late autumn rosette stage (Holm et al., 1997). Herbicides that have been found to be useful include chlorsulfuron (Swinnerton et al., 1984; Chirita and Henegar, 1985), 2,4-D + dicamba, bromoxynil + MCPA or 2,4-D at emergence in winter wheat. Effective control of L. draba in oats was obtained with chlorsulfuron, trisulfuron and fluroxypyr (Heap and Mitchell, 1992) and with glyphosate, atrazine + nopon 11E oil or a mixture of atrazine + sun 11E oil at the two-leaf stage in maize (Dobrovodski, 1975). In maize, a combination of eradicance, atrazine and 2,4-D was most effective and gave good control (Naederi and Khajehpour, 1997). In lucerne, Hernado et al. (1987) and Kontsiotou (1982) found that secbumeton gave good results, whereas in lentil, prometryn provided the best control of different broadleaved weeds including L. draba, and gave the highest crop yields.

In fruit tree orchards, norflurazon (Monserrat-Delgado, 1995), simazine at pre-emergence followed by glyphosate (Sarpe et al., 1989), simazine + paraquat, aminotriazole + diuron + bromacil + glyphosate, or terbumeton have all been used (Budoi et al., 1981). Glyphosate (Kafadaroff, 1977; Brattain and Fay, 1980) has been used successfully in vineyards and in oak plantations (Wallis, 1978; Waterhouse and Mahoney, 1983). Combination treatment of 24% urea and 6% yolk gave excellent control in pistachio fields (Davarynejad and Ak, 2001). Other effective herbicides reported were chlorsulfuron or metsulfuron applied during the budding or early bloom stages; picloram, but with little effect (Elpel, 2000); and imazethapyr, which provided >90% control in lucerne/Dactylis glomerata pastures only during the year of application (Stougaard et al., 1999).

Problems in the chemical control of L. draba have been reported by Julliard and Ancel (1973) in France, by MAFF (1977) in the UK and by the Tasmanian Department of Agriculture (1978) regarding aminotriazole, glyphosate and metribuzin. However, the short period of maximum C allocation to the below-ground tissues, the large proportion of below-ground tissues, and the wide variation of phenology among plants at a given time may account for the difficulty in chemical control of L. draba (Miller et al., 1994).

Biological Control

Lipa (1981) studied the monophagous silver mite, Aceria drabae, as a suitable species for biological control of L. draba. It did not attack any other crucifer growing in the vicinity of the weed, and was able to colonize it successfully. The mite first attacks the flowers, penetrating the seeds; flower heads become completely damaged and infested plants do not set seed (Lipa, 1976; Lipa et al., 1977). The shoot-eating beetle, Ceuthorhynchus turbatus, has also been found to attack L. draba, feeding on stems, killing or weakening the plant (Lipa, 1974). Sobhian (1976) observed the chrysomelid Colaphellus hoeftii feeding on L. draba in Iran. The adults and larvae were capable of denuding young plants of vegetation and preventing them from flowering. Larvae fed on groups of immature plants. Volatile materials from leaves of Artemisia absinthium have been reported to inhibit growth of L. draba seedlings and aqueous extracts of its leaves can prevent weed germination (Chirca and Fabian, 1973).

Integrated Control

Integrated control of L. draba includes prevention, education, early detection and eradication. Prevention is integrated with cultural, physical, mechanical, biological, chemical and monitoring methods of control and includes banning hay, grinding seeds with lucerne hay or barley grain, thus reducing weed emergence by 98-100%. Rigorous processing during manufacturing of hay/grain pellets can reduce the risk of disseminating weed seeds from pelleted feed (Cash et al., 1998). Only certified weed-seed-free hay should be used, equipment should be pressure-cleaned before entering national parks and common gardens (Olliff et al., 2001), new infestations should be surveyed, and vehicles (especially the undercarriage) should be careful cleaned by washing after driving out of an infested area (http://mtwow.org/whitetop.html).

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