Cardaria is from the Greek word for heart, Kardia, and refers to the heart shaped pods.
Draba is from the Greek word drabe meaning sharp, acrid or burning and refers to the peppery taste of the seeds and leaves.
Hoary Cress is derived hoary or whitish appearance of the foliage due to the covering of fine hairs and cress is an old English word referring to mustards.
Other Names:
Hoary Cardaria - refers to it frosted or hoary appearance of the leaves.
Hoary Pepperwort
Heart-podded Hoary Cress - refers to its hear shaped seed pods and its resemblance to Hoary Cress
Whit Top - because of its cluster of white flowers on top.
White Weed - refers to its numerous small white flowers.
Whitlow Pepperwort
Thanet Cress
Summary:
An erect, perennial herb spreading from rhizomes and reaching a height of some 900 mm with grey-green, softly downy stem-clasping leaves and clusters of many small, white, 4 petalled flowers on top in spring.
Description:
Cotyledons:
Two. The cotyledon is oval, hairless, with rounded tips, 8 to 15 mm long overall with a petiole 3 to 5 mm long. Tip rounded. Base tapered. Small water filled pimples cover the upper surface. The seedling has a long hypocotyl but no epicotyl.
First leaves:
The leaves arise singly but the first two leaves appear very closely together and give the appearance of being paired. The early leaves have an oval blade with rounded tips and an uneven margin, 8 to 12 mm long, with a petiole of the same length and are hairless.
Leaves:
Alternate.
Rosette and Lower Stem leaves:
Petiole - Short and merging.
Blade - 25-100 mm long, egg to wedge shaped, covered with fine white hairs giving a hoary appearance or grey green. Edges smooth or irregularly toothed, wavy.
Upper Stem leaves -
Petiole - None.
Blade - 10-80 mm long, clasps the stem, oblong to egg shaped, covered with fine white hairs giving a hoary appearance or grey green. Edges smooth or irregularly toothed, wavy.
Stems:
The stems are erect and not usually branched except for short branches towards the top. The stem is 150-900 mm long, erect, rigid, solid and pithy, circular in cross section with shallow longitudinal ridges, and carries very short hairs, which are difficult to see with the naked eye.
Flower head:
The inflorescence is a dense, terminal, flat topped or umbrella shaped, cluster(corymb) of flowers and tends to be rather broad and umbrella shaped.
Flowers:
The clusters of flowers are fragrant and 4-10 mm in diameter with 4 petals and carried on stalks.
Ovary -
Sepals - 2.5 mm long
Petals - 4, white, 2-5 mm long.
Stamens - 6
Anthers -
Fruit:
1 or 2 seeded, 2 celled, reverse heart shaped capsule, almost hairless, 2-4.5 mm long by 3-5 mm wide with network venation on the surface and the obvious style at the top. Borne on 8-15 mm long stalks. The two cells split from each other and fall, as a small nut, carrying the enclosed pendulous seed.
Seeds:
Dull red brown, flattened, oval to egg or tear shaped, 0.5-2.2 mm long by 0.5-1.5 mm wide, Surface slightly granular and grooved on one side.
Roots:
Taproot to 2000 mm deep with many creeping, branched, cord like, relatively horizontal roots that sucker freely.
Key Characters:
Biology:
Life cycle:
Perennial. Germination occurs in the autumn and the leaves arise singly but the first two leaves appear very closely together and give the appearance of being paired. A rosette forms over winter as the plant develops an extensive root system. Foliage dies off with the onset of summer. Flowering is often delayed until the following spring, 18 months after germination. Shoots from the crowns and buds on the roots mainly emerge in autumn with some emerging in spring. The main growth occurs in spring and early summer. Flowering stems form in late winter and early spring and flowering occurs from September to November. The perennial root system is long lived and the density of top growth varies from year to year. Injury of the roots by cultivation usually results in the formation of new shoots, which may be out of season.
Physiology:
Reproduction:
By seed and perennial roots.
Flowering times:
August to December in SA.
Spring to early summer in NSW.
September to November in WA.
Seed Biology and Germination:
Each plant produces 1000 to 5000 seeds with an 80% viability.
Seeds may remain viable for at least 3-4 years.
Heat from grass fires appears to break the dormancy of seeds.
Vegetative Propagules:
Roots and root fragments.
Hybrids:
Allelopathy:
The roots release substances that inhibit the growth of cereals and especially Wheat.
Population Dynamics and Dispersal:
Propagation via the perennial root stock is probably more important than spread by seed. Root fragments readily regenerate and injury to the root system by cultivation generally leads to increased infestations. Much of the spread can be attributed to the movement of root fragments by machinery.
The roots of a single plants can spread over a 3.7 m diameter area in one year and produce 455 shoots.
Seed is spread by stock and as a contaminant of grain and produce.
Origin and History:
Central Asia and the Mediterranean.
It established in Australia in the 1880's and quickly spread until the advent of hormone herbicides after the second world war.
Distribution:
ACT, NSW, QLD, SA, TAS, VIC, WA.
Hoary Cress occurs in most parts of Tasmania but is most common in the South and South Midlands.
It is an important weed of the eastern states of Australia.
There are scattered infestations in the Wheat belt of WA which have been targeted for eradication.
It is an important weed of New Zealand, North America, South Africa, Spain, Romania and Iran.
Habitats:
Prefers dry unshaded situations up to sub alpine altitudes.
Climate:
Warm temperate regions.
Most abundant in areas with an annual rainfall of 400 mm or more.
Soil:
Tolerates a wide range of soils and prefers heavy fertile soils, alluvial river flats, alkaline, alkaline black soils and red clay loams. It is usually less prolific on sandy surfaced soils.
Plant Associations:
Significance:
Beneficial:
Seeds used as a pepper substitute.
Leaves used as a vegetable in Afghanistan.
Detrimental:
It is a major weed along roadsides and railway lines, and occurs commonly in run down pasture and waste areas.
It causes serious yield reductions and may interfere with harvesting in cereal and other crops.
It is allelopathic and reduces the germination and growth of companion plants and especially cereals.
In established lucerne it can be competitive if present in large numbers.
Weed of vegetables, orchards and vineyards.
In the Victorian Wimmera it was regarded as the worst weed of cereal crops before the discovery of phenoxy herbicides.
Taints milk and meat for about a week after ingestion.
Unpalatable.
It may carry viruses and diseases of Brassica crops.
It is a weed of both cultivation and minimum tillage systems.
Toxicity:
Toxic but rarely eaten in sufficient quantity to cause problems.
Young leaves contains HCN (prussic acid) and are suspected of poisoning stock. It is also used as a fish poison.
Legislation:
Noxious weed of NSW, SA, TAS, VIC, WA.
Management and Control:
Difficult to control.
Thresholds:
Eradication strategies:
Avoid cultivation unless it can be repeated every time shoots appear for a period of two years or more. Monthly cultivations for 3-4 years have been successful overseas.
Phenoxy (hormone) herbicides at the early flowering stage initially then as shoots appear, glyphosate, amitrole, picloram, sulfonylurea herbicides and fluroxypyr have given good control.
Flooding for 2 months provides control in irrigation areas.
Most of the Brassicaceae weeds have dormant seeds that continue to germinate throughout the season and for several years. They often mature and set seed very quickly. Manual removal is effective but must be done at least every 8-10 weeks. Once pods are formed, seed will often mature even if the plant has been uprooted. Soil disturbance often leads to a flush of seedlings.
Many are somewhat unpalatable, so grazing only offers partial control. They often flourish in undergrazed, sunny areas.
In bushland situations, fairly selective control can be achieved with 100 mL spray oil plus 0.1 g Eclipse® or 0.5 g Logran® in 10 L water. 5 mL Brodal® is often added to this mix to provide residual control of seedlings. Spray the plants until just wet from the seedling stage up to pod formation.
Isolated plants should be removed manually and burnt if flowering or seeding and a 10 m buffer area sprayed with 10 mL Brodal® in 10 L water.
500 mL/ha of glyphosate(450g/L) can be used at flowering to reduce the seed set of most species on roadsides without causing significant damage to most native plants.
Wick application with 1 part glyphosate(450g/L) in 2 parts water or overall spraying with 100 mL glyphosate(450g/L) in 10 L water provides reasonable control of most species though Wild Radish tends to regrow.
Herbicide resistance:
Closely related species differ considerably in their response to herbicides. If unexpected herbicide failures occur take a flowering and fruiting sample to the state herbarium for accurate identification.
Biological Control:
A number of bio control agents are being investigated.
Related plants:
None.
The native Brassicaceae species usually have short, broad and smooth pods.
Plants of similar appearance:
White Weed is similar in appearance to Field Cress, but in the mature stage can be distinguished from it by the presence of a spreading root system and by the inflorescence which in this species is broad and spreading while in Field Cress it is elongated and conical. The seedlings are difficult to differentiate. In White Weed the cotyledons are slightly more pointed and the first leaves tend to be pointed with distinct small lobe while in Field Cress the leaf is only bluntly pointed or rounded at the tip and without lobes.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P132. Photo.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P383. Diagram.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P186-188. Diagram.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P320. Photo.
Gardner, G.A. and Bennetts, H.W. (1956). The toxic plants of Western Australia. (West Australian Newspapers Ltd, Perth). P34.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P48-49. Diagram.
Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P86-87. Diagram.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #250.1.
Lloyd, S. (2000). Hoary Cress. Agriculture WA Farmnote No. 40/00.
Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P84-86. Diagram. Photo.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P339-341. Diagram. Photo.