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Common Name Black knapweed Botanical Name Centaurea nigra L. Status Black knapweed is one of only fourteen weeds proclaimed as State Prohibited Weeds in Victoria. This is the highest category to which a noxious weed can be allocated and means that black knapweed is to be eradicated if possible from the State. Origin Black knapweed is native to Europe. It may have been introduced to Victoria as an ornamental plant. Description An erect perennial herb with creeping roots, growing to around 1 m high. Stems - ridged, hairy and rough to touch, initially green but turning purple as they mature. Leaves - grey-green to green, hairy, rough to touch, oblong or lanceolate. Rosette leaves and leaves at the base of stems are variable in shape, sometimes with toothed margins, smooth margins or deep lobes, and up to 25 cm long. Stem leaves are smaller and lack stalks. Flowers - reddish purple with large forked outer petals. Flower heads are globe-shaped and 3 to 4 cm in diameter and occur singly at the end of a stem branch. Bracts around the flower head are black or dark brown, hairy and dissected at the tips. Seeds - 3 to 4 mm long and light brown. Seeds may have a pappus of a few short bristles or none at all. Roots - extensive; grow both vertically and horizontally producing new shoots and top growth. Life Cycle Seeds usually germinate in autumn and spring. Top growth is produced in August/September from shoots and existing plants. The plant usually flowers in November to March and the top growth dies off in late autumn. However if conditions are suitable black knapweed will germinate and flower at any time of year.  Figure 1. Black knapweed. Dispersal Black knapweed seeds are not spread more than a metre or two from the parent plant with normal winds. The usual means of spread are:
General Black knapweed is not readily eaten by cattle. Sheep may graze it in the rosette stage. Black knapweed appears to produce chemicals which inhibit germination and growth of plant species that would otherwise compete with it. The distribution of black knapweed in Victoria is currently limited to the Ovens Valley around Bright, and areas near Ballarat and Warrnambool and in Gippsland. Chemical Control Under Victorian legislation there are controls on various aspects of the uses of agricultural chemicals. Some particular uses are prohibited and some require permits. Users of certain agricultural chemicals are required to obtain an Agricultural Chemical User Permit (ACUP) or work under the direct supervision of an ACUP holder. Additional restrictions on the use of some herbicides apply to particular geographic areas known as Chemical Control Areas (CCA). It is the responsibility of chemical users to familiarise themselves with these controls. See Agriculture Note: Agricultural chemical user permits (ACUP) and chemical control areas(CCA) for further information. An ACUP is required for the use of prescribed chemicals containing the active constituents marked with an asterisk (*) in the following list. Records of the use of these chemicals must be made by the user and these records must be kept for 2 years. Restrictions on use in CCAs apply to the chemicals marked with a hatch (#). Contact the Regional Chemical Standards Officer of the Department of Natural Resources and Environment if further advice is required. You should read the product label and follow all label instructions carefully before using any herbicide. Use a product containing one of the following active constituents or combinations of active constituents that is registered in Victoria to control black knapweed in the particular situation in which you need to use chemical control, eg. in pastures. Consult the product label for detailed information on restrictions on use.
This list of chemicals is based on information supplied to the Department of Natural Resources and Environment by the National Registration Authority for Agricultural and Veterinary Chemicals (NRA). The State of Victoria through the Department of Natural Resources and Environment has not assessed or checked the accuracy of the information supplied to it from the NRA as that responsibility rests with the NRA. Important Any person who believes they have located an infestation of black knapweed, regardless of the area, please notify a Catchment Management Officer at a local office of the Department of Natural Resources and Environment. Reference Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious Weeds of Australia. Melbourne, Inkata Press Acknowledgements Prepared by R Williamson; KTRI 1996. Updated by I. Faithfull, KTRI, January 1998. Active constituents information supplied by Chemical Standards Branch December 1997. This note replaces note number PPA0001 The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. |
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© The State of Victoria, 1996 - 2008.
This document was published on 26/10/2008.