Why Is It A Weed?
What are its impacts?
Hoary Cress (Lepidium draba) is a significant weed of crops, reducing yields through competition. It is widespread on arable land, waste ground and roadsides drainage lines and irrigation ditches and can spreads to nearby areas or further by water.
Agriculture: In Australia, it is a weed of grain crops, pastures and horticultural crops such as vegetables, orchards and vineyards, and causes serious yield reductions and may interfere with harvesting in cereal and other crops It is a weed of both cultivation and minimum tillage systems. In established lucerne it can be competitive if present in large numbers. It is seldom grazed but milk and meat may become tainted if plants are consumed for about a week after ingestion. It has poisonous properties and is suspected of causing stock losses but rarely eaten in sufficient quantity to cause problems. Established infestations are very difficult to eradicate, mainly because of the vigorous perennial root system. The roots of Hoary Cress contain chemicals that hinder the germination and growth of companion plants, especially cereals. Infestations can completely dominate fields and, when in flower, form massive drifts of white (Faithfull 1998; Agriculture Western Australia 2005; Parsons & Cuthbertson 2001; DPIW 2002). A highly competitive weed and may carry viruses and diseases of Brassica crops. As it is part of the Brassica family, it poses a major problem when canola or similar cops in the family are grown is part of the cropping rotation, as it cannot be controlled in-crop (DPI NSW 2019).
Native ecosystems: Not normally a weed of native areas, but found in disturbed riparian areas.
Urban areas: A weed of roadsides, creeks and drains and potentially parks and gardens.
How does it spread?
Hoary Cress can spread by the dispersal of both seed and root fragments, and through the growth of lateral roots
Hoary Cress has an extensive and persistent root system and most new plants arise from its spreading roots and broken root segments. The well developed lateral roots produce new shoots from buds that occur along its length. Cultivation is a common cause of root spread (DPI NSW 2019). Regeneration of plants from root fragments following cultivation is rapid and this is the primary means of spread for this weed species (Faithfull 1998; Parsons & Cuthbertson 2001; DPIW 2002). In a trial in Tasmania, root fragments of 2 cm long that were buried 10 cm deep readily emerged (DPIW 2002). Spread by contaminated soils on machinate and vehicles and earth works.
Thousands of seeds are produced per year by each plant, with around 80% viability. Seeds can be spread by contaminated soil, hay, grain, vehicles and equipment (DPI NSW 2019). It is a prolific producer of seed, with up to 850 fruits being produced per flowering stem (Lyons 1998). Seed may be an insignificant method of reproduction in established infestations but can be a significant method of spread into new areas (DPIW 2002). Seeds of Hoary Cress spread in the same manner as other similar weedy cruciferous species such as Wild Radish (Raphanus raphanistrum) and Sand Rocket (Diplotaxis tenuifolia). The seed of these species spreads by water, especially where plants grow in riparian habitats and on steep terrain where erosion and runoff occurs.
General spread for seed are contaminated soil, fodder, vehicles and cultivation equipment and seeds and roots may also be readily dispersed along roadsides during roadside maintenance works. Dispersal via contaminated agricultural produce is also a potential means of spread (Parsons & Cuthbertson 2001).
What is its history in Australia?
Hoary Cress was first recorded in Australia in 1882, from Hobart, Tasmania, and soon after from Victoria in 1883. It was later recorded at Dubbo, New South Wales in 1898. It had reached Merredin, Western Australia, and the Darling Downs, Queensland, by the early 1920s. Seeds of Hoary Cress were most likely introduced into Australia as a contaminant of imported crop or pasture seeds. It was not until the 1930s that the importance of this species as a crop weed was realised. It competed strongly with wheat crops, could not be controlled easily, was readily spread by cultivation and detrimentally changed the suitability of once prime agricultural land for crops (Parsons & Cuthbertson 2001).