Cardaria spp.
From BugwoodWiki
Author: Kelly E. Lyons, University of California at Davis, ed. Barry Meyers-Rice, Global Invasive Species Team, The Nature Conservancy
Contents |
Identifiers
Latin Names: Cardaria draba (L.) Desv, Cardaria chalepensis (L.) Hand-Maz., Cardaria pubescens (C.A. Meyer) Jarmolenko
Common Names: Hoary cress, whitetop
Names
Cardaria draba (L.) Desv. is a member of the mustard family (Brassicaceae). It has had a number of botanical names. It was originally included in the
genus Draba (Fernald 1950), and more recently in the genus Lepidium (as Lepidium draba L.). Today, most sources place the species in the genus
Cardaria. The genus name derives from the Greek word kardia (heart), and refers to the heart-shaped fruit of C. draba (Gleason, 1952). However,
not all the fruit in this genus are heart-shaped.
A study by Bellue (1933) showed that the North American weed referred to as Cardaria draba actually consisted of three European and Asian species:
C. chalepensis (L.) Hand.-Maz., C. pubescens (C.A. Mey.) Jarmolenko, and C. draba L.
The nomenclature for C. chalepensis (L.) is confusing. It is closely related to C. draba, and some authors reduce it to subspecific or varietal
status, calling it C. draba subsp. chalepensis (L.) O.E. Schulz or C. draba var. repens (Schrenk) O.E. Schulz; furthermore, it is believed
to hybridize with C. draba (Hickman 1995; Mulligan & Findlay, 1974). Cardaria chalepensis may also be referred to as Lepidium chalepense L. or
Lepidium repens (Schrenk) Boiss. (Mulligan & Frankton 1962). The specific epithet is frequently misspelled "chalapensis." Cardaria pubescens
is sometimes referred to as Hymenophysa pubescens C.A. Mey. (Robbins et al. 1952). In this treatment, the three plants, C. chalepensis (L.)
Hand.-Maz., C. pubescens (C.A. Mey.) Jarmolenko, and C. draba L. will be treated as separate species.
Common names for mustards abound, and the same common names are often used for plants in other mustard genera. Cardaria species are commonly called
hoary cress, white weed or white-top. Common names for C. draba are heart-podded hoary cress, whitetop (Fischer et al. 1978), perennial
peppergrass (Kummer 1951) and Cranson dravier (Mulligan & Frankton 1962). In England it may be referred to as whitlow pepperwort or Thanet weed (Robson
1919), hoary pepperwort, chalk weed and devil’s cabbage (Garrad 1923). Common names for C. chalepensis include lens-podded hoary cress (Fischer et
al. 1978) and Cranson rampant (Mulligan & Frankton 1962). Common names for C. pubescens include globe-podded hoary cress and Cranson velu (Mulligan
& Frankton 1962).
Description
Cardaria draba is a hardy perennial with stout, erect or procumbent stems that can grow 2-5dm tall. The plant is leafy below and branching above with
grayish stems (Jepson 1953). Plants are glabrous or nearly so at the top and densely hairy below (Mulligan & Findlay 1974). In general, they have a gray-
green, soft hairy appearance (hence the name hoary).
Seedlings are distinguished by their hypocotyl, which is dull brown-green, but green above. Seed leaves are 2.5x7-9mm, pale, dull gray-green, with a
sharp, pepper taste. While young, the leaves are more or less opposite below but alternate above and obscure the stem. Leaves are rolled in bud (Kummer
1951).
Mature C. draba leaves are blue-green, 1.5-7.5 (or even 10) cm long (Fernald, 1950), and are broadly ovate to obovate (Fischer et al. 1978). The
lower leaves are long, slender, and taper to a short petiole (Robbins, 1952; Mulligan & Frankton, 1962). The margins are irregular, and may be either
smooth or toothed. The leaf surface is weakly to densely hairy (Mulligan and Findlay 1974). These leaves wither before the flowers open (Scurfield 1962)
and are shed as the seeds mature (Selleck, 1965). The upper leaves are shorter and broader (Fischer et al. 1978). They lack developed petioles, and
clasp the stem. The leaf bases may have two sagittate lobes (Fischer et al. 1978; Mulligan & Frankton 1962).
Cardaria draba blooms in early spring and looks like conspicuous patches of snowy white (Robbins et al. 1952; Fischer et al. 1978). The showy
inflorescences consist of many white flowers in a flattened corymb of racemes. The flower pedicels (stalks) diverge slightly from the stem. Each flower is
2mm wide, and has four petals with long narrow bases, like a spoon (Robbins et al. 1952; Mulligan & Findlay 1974). The sepals are green and 1.5-2.5mm
long. Like other mustard species, there are six stamens and one pistil.
Cardaria draba fruit is 3-4mm long and is shaped like an inverted heart. Each of its two chambers usually contains one or two seeds. The fruit is
hairless and has a distinct beak (persistent style) on the upper end. As the fruit dries it deflates and the veins become distinct (Scurfield, 1962). The
seeds are oval or round at one end and narrow to a blunt point at the other. They measure 2-3mm long by 1-1.5mm wide and are dark red-brown (Fischer 1978;
Robbins et al. 1952).
Distinguishing C. draba from C. chalepensis and C. pubescens
Cardaria draba, C. chalepensis, and C. pubescens are easily confused, especially since they can occur in mixed stands (Bellue 1933). The
description of C. draba given above applies equally well to C. chalepensis and C. pubescens, except for details given below.
Cardaria chalepensis is slightly shorter (20-40cm tall, as opposed to 20-50 cm for the other species). The fruit is oval to lens-shaped (Mulligan &
Findlay 1974), has a longer style, and does not narrow at the septum (i.e., where the two chambers of the silicle meet). The fruit remains inflated when
mature and is not conspicuously veined once dry (Robbins et al. 1952). Hybrids of C. chalepensis and C. draba may occur, but the progeny has not
been described (Mulligan & Frankton, 1962). Each fruit usually contains four seeds, while C. draba usually has two seeds per fruit, (Miller & Callihan
1991) but this characteristic is unreliable.
Cardaria pubescens fruit and sepals are hairy and the fruit is taller than wide or globose and remains inflated when dry. Like C. chalepensis,
the fruit of C. pubescens usually contain four seeds (Miller & Callihan 1991). The flower pedicels of C. chalepensis are held closely to the stem,
giving the inflorescence a cylindrical appearance. (Pedicels of C. draba are not held as closely to the stem.) Finally, C. chalepensis foliage has
a purplish cast when flowering and in fruit (Robbins et al. 1952).
Distinguishing Cardaria from Lepidium
Species of Cardaria are often confused with those of Lepidium, but they can easily be told apart by both leaves and fruit characteristics. The
upper leaves of Lepidium species clasp the stem to form a complete ring of tissue (i.e. they are perfoliate), while those of Cardaria do not. The
fruit of Lepidium is flattened, keeled or winged while that of Cardaria is rounded or inflated. Finally, the fruit of Lepidium is dehiscent while
the fruit of Cardaria is indehiscent (Mulligan & Frankton 1962; Gray 1970).
Stewardship summary
General
Cardaria draba, C. chalepensis and C. pubescens were transported from southwest Asia near the beginning of the 20th century. Cardaria
draba and C. pubescens are more common in the United States, while C. chalepensis is more widespread in Canada.
These three perennial species have deep, long-lived taproots that store sugars. The plants can spread rapidly. Intact or damaged roots left behind after
control efforts can resprout. The hoary cresses flower early in the season and form large white patches in fields.
The various hoary cresses can be identified using hairiness and fruit-shape characters. The fruit of C. draba is heart-shaped, that of C.
pubescens is globe-shaped and that of C. chalepensis is more oval or lens-shaped. The fruit and sepals of C. pubescens are hairy.
The three species grow in a variety of habitats, but thrive in disturbed or irrigated areas. They are less of a problem in undisturbed settings. The most
successful control efforts combine several management practices such as herbicide application and physical removal by hoeing or tilling, followed by
competitive species plantings. The most effective herbicides are 2,4-D and amitrol. Chemicals provide the most control when applied at the early bud or
flowering stage. This is presumably when carbohydrates are moving from above to below ground and herbicides are more likely to be transported to the
roots.
Impacts and threats
Although C. draba is found through the United States, it causes most of its trouble in the west (Robbins et al. 1952). Hilgard (1890) branded it
the most dreaded of the perennial weeds. It reduces agricultural yields, particularly grain crops, alfalfa crops, and orchards (Chipping 1992). It
displaces valuable rangeland forage species and is toxic to livestock (Fischer et al. 1978). Managers of The Nature Conservancy consider C. draba
to be a relatively easily controlled wildland weed that poses moderate threats to habitat and other plant species. It reduces native biodiversity and
forage quality. Disturbed sites are the most threatened. Types of disturbance which promote colonization and spread include grazing (Carr, 1995),
irrigation, and cultivation (O’Brien & O’Brien 1994).
In the United States, C. chalepensis is less widespread than C. pubescens and C. draba, but in Canada it is the most troublesome hoary cress.
Cardaria chalepensis is particularly aggressive in irrigated areas (Mulligan & Findlay 1974) although in central Asia it is also a problem on non-
irrigated soils (Keller et al. 1934).
All three species are listed under the Seeds Act and Regulations in Canada as Prohibited Noxious Weed Seeds (Mulligan & Findlay 1974). Commercial seed
cannot be imported into the United States if it is contaminated with any of the hoary cresses (Rollins 1967).
Natural history
Global range
Cardaria species are native to southwest Asia, although the range of C. draba extends into southeast Europe (Mulligan & Frankton 1962).
Cardaria draba is a widespread weed (Mulligan & Findlay 1974). It is considered a serious weed in Afghanistan, Austria, Hungary, Italy, the former
Soviet Union, and the United States; it is a principle weed in Greece, Iran, Jordan, and former Yugoslavia; it is a common weed in Canada, England,
Germany, Iraq, Lebanon, Portugal, South Africa, Tunisia, and Turkey; it is present as a weed in Argentina, Belgium, Chile, Czechoslovakia, Guatemala,
Israel, The Netherlands, New Zealand, former Rhodesia, and Tasmania (Holm et al. 1991). It is found throughout Europe as far as 65° N in Finland.
In the USA, Cardaria draba is found in the west from Colorado and Wyoming to California (Fischer et al. 1978; Munz & Keck 1959; Britton & Brown
1970; Kummer 1951), and in the east coast from Washington D.C., north towards (but not including) Nova Scotia (Fernald 1950). Crons & Frankton (1952)
report it in all the Canadian provinces except Prince Edward’s Isle, Nova Scotia and Newfoundland.
Cardaria draba probably traveled to the USA in ship’s ballast or contaminated alfalfa (Mulligan & Findlay 1974). It was first collected in North
America in Yreka, California in 1876, and Ontario, Canada in 1878 (Robbins 1940; Mulligan & Findlay 1974). Other collections, such as in Napa, California
(in 1893), a southwestern alfalfa field (in 1898), and New York City (also in 1898) firmly established its presence on the continent (Robbins 1940;
Robbins et al. 1952).
Cardaria chalepensis was introduced to North America approximately 20 years after C. draba was, and probably arrived in alfalfa seed from
Turkestan (Mulligan & Frankton 1962). Early collections were made in the USA in Chino, California (in 1918) and in Alberta, Canada (in 1926) (Mulligan &
Findlay 1974). Today, C. chalepensis is more widespread and persistent in western Canada than it is in the USA (Mulligan & Frankton 1962).
Cardaria pubescens probably arrived in infested alfalfa seed from Turkestan (Mulligan & Frankton 1962), and was first collected on North America in
1919, both in Alberta, Canada and Michigan (Mulligan & Findlay 1974; Robbins et al. 1952). It is more common in the northwestern USA with a few
occurrences in the mid-west (Mulligan & Frankton 1962).
Habitat
They can grow in a variety of non-shaded, disturbed conditions, including roadsides, waste places, fields, gardens, feed lots, watercourses, and along
irrigation ditches (Hickman 1995; Fernald 1950; Selleck 1965). Preserve managers for The Nature Conservancy find C. draba in a variety of upland
habitats including open grasslands and fields, but also at the edge of riparian habitats (O’Brien & O’Brien 1994), and as a minor component of
aspen/willow communities (Carr 1995).
These species are not particular about soil type, and can grow in heavy (i.e. > 50%) clay, or light, sandy, or gravelly loams (Mulligan & Findlay 1974;
Robson 1919; Scurfield 1962). They are salt-tolerant, but Cardaria draba prefers non-acidic soils (Hickman 1995; Scurfield 1962). They are most
aggressive in irrigated conditions or during moist years (Mulligan & Findlay 1974). Selleck (1961) found that populations of C. chalepensis and C.
pubescens increased when rainfall was higher than normal and decreased when rainfall was low. At many Kansas infestations, the water table was likely to
be at or near the surface for some part of the growing season (Frazier 1943).
Biology
In the United States C. draba flowers in late May or June, and fruits from mid-July into August (Gleason & Cronquist 1991; Fischer et al. 1978).
In California, C. chalepensis completes seed maturation before C. draba (Bellue 1933).
In Saskatchewan, Canada, C. pubescens sown in October were 5-13 cm tall with 5-7 leaves by 18 May. On July 7, some flowers were open. Fruits were
fully developed by July 14 and by July 20 seeds were immature but developed (Selleck 1965).
In Colorado greenhouse and outdoor tests, C. draba cotyledons appeared 5-6 weeks after planting (Simonds 1938). Fully developed basal rosettes formed
after three weeks, lateral roots developed after 2-3 weeks, and aboveground branching began after 13-14 weeks.
Flowers, Seeds and Dispersal
Cardaria draba and C. chalepensis can self-pollinate and produce up to 850 fruits per flowering stem. Each fruit contains approximately two seeds
(Corns & Frankton 1952). Cardaria pubescens plants produce 30-560 fruits per plant (averaging 300 fruits) (Selleck 1965).
Seeds germinate well. Germination rates are 93% for C. draba and 98% for C. chalepensis (Bellue 1946). Seed viability decreases with age,
especially rapidly for C. draba--germination rates for the three years after seeds were produced were 84%, 31%, and 0%. The seedbank for C.
chalepensis is more persistent--after three years, 52% of C. chalepensis seeds still germinated. The optimal germination temperature for C.
draba is between 20-30°C.
Seeds can be transported a number of ways. They may be moved by water in drainage ditches. They can be inadvertently spread by human activity, since the
seeds can contaminate crop seeds or the soil in root crops. In this way they are dispersed along roadsides and railways (Groh 1940). Populations located
along roads and ditches should be controlled to avoid dispersal of the seeds to other locations. Cardaria draba is known to seed very freely (Robson
1919).
Shoots and roots
Cardaria grows most rapidly in the absence of competition. In Saskatchewan, Canada, C. draba grew to 3.7m in diameter in its first year. In
following years, C. draba, C. chalepensis and C. pubescens expanded approximately 0.6-0.8m per year (Selleck 1965). Meanwhile, infestations of
all three species contracted when in competition with other species (particularly other perennials) and when not irrigated.
The hoary cresses can regenerate from their thick roots. These roots can grow a few meters or more deep (Garrad 1923; Robbins et al. 1952; Selleck
1965; Frazier 1943; Corns & Frankton 1952). Lateral roots grow for long distances and then produce more plants (Scurfield 1962).
These large root systems are produced quickly. A 25-day old C. draba plant will develop a taproot 25cm deep and 5-6 horizontal roots with numerous
vegetative buds. At 100 days they have approximately 48 shots in an area within 30 cm of the plant, and an additional 80 root buds (Scurfield 1962).
Severed root segments only 1.3cm long can regenerate into new plants if they are left within approximately 7-10 cm of the soil surface (Scurfield 1962).
Sugar production
The best time of the year to apply herbicides to Cardaria is late in the season, when the herbicide will be transported into the extensive root system
and kill it. A Colorado study found that the roots accumulated sugars mostly during the period extending from late April-early May through late June-early
July (Barr 1942). Thus, the optimal time to apply herbicide in Colorado was in early summer. Generally, accumulation of sugar in the roots coincides with
the onset of flowering.
Cold Tolerance
Cardaria draba is able to tolerate very cold climates. It grows in Finland, where the average temperature in July is 15-17°C (59-63°F) and the
number
of days with above freezing temperatures is 120-140 (Scurfield 1962). Cardaria chalepensis and C. pubescens are common agricultural pests in
Canada as far north as 54° latitude (Mulligan & Findlay 1974).
Management/Monitoring
Because they can regenerate from their extensive root systems, the hoary cresses readily re-establish after eradication measures. Therefore, control must
be persistent, and requires at least 2-3 years of follow-up work (Blackman et al. 1939; Garrad 1923; Willis 1950).
Successful control is most likely achieved with a combination of approaches. Selleck (1965) used a combination of mowing and competitive cropping to
control C. chalepensis and C. pubescens. O’Brien and O’Brien (1994)--managers for The Nature Conservancy--controlled C. draba by ceasing its
irrigation, removing outlying plants, and increasing the general health of the grasslands they were managing. Other managers for The Nature Conservancy
have decreased grazing (Carr 1995), or developed restoration plans (Hill 1995).
Prevent new infestations originating from seed sources. Seed may travel in contaminated hay, on farming equipment, and in fresh manure (Carr 1995).
Cardaria seeds have been eliminated from manure after one month of decomposition under very moist, warm conditions in late summer (Anonymous 1970).
Biological Control
No biological control agents are available for hoary cress (Miller & Callihan 1991). Below is a list of potential bio-control agents for C. draba.
Insects found on C. draba in central Europe:
Homoptera: Brevicoryne brassicae L., and Myzodes persicae Sulz.
Lepidoptera: Pieris brassicae L., and P. napi L.
Coleoptera: Ceutorrhynchus turbatus Schul. (larvae on silicles), Phyllotreta namorum L. (larvae on leaves) (Mulligan & Findlay 1974), Meligethes spp., and Nacerdes sp. (Scurfield 1962).
Diptera: Phytomyza horticola Gour., and Scaptomyza flaveola Meig. (both larvae on leaves) (Mulligan & Findlay 1974).
Hymenoptera: Halictus spp. (Scurfield 1962).
Fungus, parasites, and diseases found on C. draba:
Cercospora bizzozeriana Sacc & Berl. (Mulligan & Findlay 1974), Albugo sp. (Chev.) Kunth, and Peronospora lepidii-sativi Gaum. (Scurfield 1962).
Cultural practices
The hoary cresses are most invasive in agriculture when they are irrigated. In less disturbed settings without irrigation, and in competition with other
species (particularly perennial shrubs) they are relatively easily controlled. In moist conditions, alfalfa is a better competitor with C. chalepensis
than perennial shrubs are, and in a combination of alfalfa cultivation and mowing 2-3 times per year will eradicate C. chalepensis within 5-6 years
(Selleck 1965). Other plants that compete well against C. chalepensis (at least in Saskatchewan, Canada) were Rosa spp., Symphoricarpos
occidentalis (western snowberry), and the invasive exotic Centaurea repens (Russian knapweed).
Cutting, mowing, and grazing
Cutting is somewhat effective in controlling C. draba. A combination of weed-whacking and applying 2,4-D from a backpack sprayer has provided 50%
control at a preserve maintained by The Nature Conservancy (O’Brien & O’Brien 1994). Meanwhile, a single late-April treatment of cutting plants back to
the ground did nothing to control plants in England (Willis 1950). Cutting in this way, combined with an herbicide application, was no more effective than
using herbicides alone. If cutting is to be used, it clearly should be timed properly. Cutting before plants are flowering does little to control plants,
while waiting for the plants to be in full flower will result in smaller plants and less seed production (McInnis et al., 1990). However, McInnis et
al. 1990 recommend that cutting plants be combined with grazing as a primary or long-term solution for control of C. draba.
Sheep will eat C. draba, and especially like seedlings. Cattle that eat C. draba may have tainted milk (Scurfield 1962)
Mowing to control hoary cresses is controversial. Under non-irrigated conditions, mowing provides some control but also harms other species, especially
perennials (Selleck 1965), which are important to maintain as competitors.
Disking and hoeing
Cardaria root systems can be exhausted through repeated cultivation (Kott 1966; Barr 1942), resulting in complete elimination if the follow-up occurs
within ten days of weed reemergence (Miller & Callihan 1991). Hulbert et al. (1934) found tilling was a more economical way to remove C. draba
than were herbicides. They recommended an initial deep plowing, followed by 10-13cm deep cultivations every five days for the first six to eight weeks of
growth, and then less frequent tillings into October. Using this regimen, the plants were killed within two years. By tilling less frequently, Mulligan &
Findlay (1974) killed Cardaria after three consecutive years. Even one cultivation before seed set reduced infestations.
Rosenthal and Headley (1944, as referenced by Mulligan & Findlay 1974) successfully eradicated C. pubescens in one and a half seasons by hoeing every
four weeks.
Cultivation is generally more successful when used with a competitive crop, as described above. On irrigated land Selleck (1965) controlled C.
chalepensis in six years using summer fallowing combined with disking and planting mixtures of alfalfa and Bromus plants.
Cultivation machinery can spread Cardaria infestations, so all root fragments should be removed from machinery before it is used in other, uninfested
fields (Pemberton & Prunster 1940; Mulligan & Findlay 1974; Scurfield 1962).
Chemical
Herbicide treatment for C. draba is effective, but in most cases a multi-year commitment is required (Blackman et al. 1939; Garrad 1923; Robson
1919; Willis 1950). Cardaria draba can re-establish rapidly if control measures are stopped too soon (Willis 1950). Even so, just a year of herbicidal
treatment may help in restoration efforts where competitive plants are also being grown (Garrad 1923).
The timing of herbicide application is important. Most recommend application of herbicides at the bud or flowering stage. In a very thorough study,
Blackman et al. (1939) demonstrated that timing was important when using the herbicides MCPA (2 methyl-4-chloro-phenoxyacetic acid) and DCPA (2:4-
dichloro-phenoxyacetic acid). Both herbicides were most effective when applied to flowering shoots but MCPA was more effective on plants still in bud (77%
control) while DCPA was more effective on plants in full flower (69.4% control). Double spraying in one year did not improve control.
The three species of Cardaria differ in their susceptibility to herbicides, and C. draba is the most resistant. Jenkins & Jackman (1938) found
that the application rate of carbon bisulfide to control C. draba was almost 2.5 and 2 times greater than that for C. pubescens and C.
chalepensis, respectively. In Alberta, Canada, Sexsmith (1964) found that that the three species, C. chalepensis, C. draba and C. pubescens,
differed in their responses to 2,4-D. Furthermore, he found that some strains of C. chalepensis were resistant (this may be because in Canada, C.
chalepensis is frequently controlled using herbicides).
Unless otherwise mentioned, all entries for herbicide use apply to C. draba.
2,4-D
Apply 2,4-D LV ester or amine at 2.3-3.4kg acid equivalent/ha in non-cropland situations and 1.1kg acid equivalent/ha for selective treatment. Apply the
herbicide early in the growth stage, before flowering. 2,4-D can be used in the spring, beforehand, when plowing, but respray new growth in the fall
(William et al. 1998). Ester formulations should be sprayed only when the temperature is low, since they can evaporate at temperatures as low as
21°C
(70°F) and harm non-target plants. Vaporization increases as the temperature rises (Hall et al. 1992).
A program of using a weed-whacker on flowering plants and 2,4-D applied using a backpack sprayer, several times during the growing season, resulted in
approximately a 50% control rate (O’Brien & O’Brien 1994).
In Saskatchewan, Canada, yearly 2,4-D applications at 2.2kg/ha, combined with competition from perennial grasses, eradicated C. chalepensis after
three years (Selleck 1965).
In England, 2,4-D provided 90% control when applied for two years at .85-1.1kg acid equivalent/ha. Contrary to most other studies, these plants were
treated when only several cm tall, to flowering size. A competitive crop that is tolerant to 2,4-D should be used in the third year (Scurfield, 1962).
In Canada, 75-99+% C. chalepensis control is achieved with 2,4-D at 5.6-23kg/ha. Cardaria draba and C. pubescens are controlled to between 90
-99% at only 2.25kg/ha. Measurements made one year post-application (Sexsmith 1964).
Amitrol® and Amitrol-T®
Apply at .7kg ai/100 liters water for spot treatment before first flowers open. Wet foliage thoroughly (William et al. 1998). Commercial use of
amitrol is restricted as of 1985. It is not registered for use on crops or grazing lands.
In Canada, all three Cardaria species were controlled by 97-100% using Amitrol at 2.2kg/ha. Twice the application rate did not improve control.
Measurements were made one year post-application (Sexsmith 1964).
Ally®
An application at 35gm/ha was effective (Carr 1995).
Chlorsulfuron (Telar®)
This is effective if applied at the pre-bloom to bloom growth stage, or to rosettes in the fall at 26-53gm ai/ha (William et al. 1998). Use this with
an 80% ai surfactant. Apply only in sites not used for agriculture.
Metasulfuron (Escort®)
This is effective if applied at the pre-bloom to bloom growth stage, or to rosettes in the fall at 21-42gm ai/ha (William et al. 1998). Use this with
an 80% ai surfactant. Apply only in sites not used for agriculture.
MCPA (2-methyl, 4-chlorophenoxyactic acid)
In England, MCPA applied as a spray at 2.2 or 4.5kg/ha controlled C. draba by 96% in the first year (for both rates). Control for the two rates during
the second year was 94% and 98%, respectively. If the follow-up control was not applied during the second year, control was only 85% for both rates
(Willis 1950).
In Victoria, Australia, applications at the early rosette stage of growth provided 42% (for 1.1kg/ha), 28% (for 2.3kg/ha), and 55% (for 5.6kg/ha).
Applying at 5.6kg/ha for a second year increased control to 85%. An application rate of 2.8kg/ha may be sufficient if there is competition from other
plants (Moore 1953).
Trials at 0.09kg/100liters/ha (in England) were most effective when applied at the bud stage and for at least two consecutive years. This provided 96%
control. Double spraying each year was ineffective and wasteful. A third year of treatment may be required but was not tested in this study (Blackman et
al. 1939).
Sulfometuron Methyl (Oust®)
This is effective if applied to pre- or post-emergent hoary cress at 0.16-0.27kg ai/ha or 0.21-0.35kg/ha. The best results are obtained if the application
is made during early stages of growth. It can only be applied in non-crop areas, and with extreme care if near crops (Hall et al., 1992).
Burning
No information available on burning as a control measure.
Information sources
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