|
Horehound | LC0178 |
Department of Primary Industries
Updated: July 2007
To view the Adobe Acrobat file, you will need the Adobe Acrobat Reader (external link). |
(PDF 379kb) |
Common and Scientific Names
Horehound
Marrubium vulgare L.
Origin and Distribution
Horehound is native to temperate Eurasia, Europe, the Middle East, and the Mediterranean region including North Africa. It is widespread throughout Victoria and is common on sheep camps and in waste places.
Description
A bushy perennial plant, 30 to 80 cm high, sharply aromatic when crushed, covered with dense whitish hairs.
Stems - Four-sided, up to 60 cm high, stout, branched, upright to trailing, densely hairy, whitish, and woody at the base.
Leaves - Opposite, broadly oval to round, 1 to 3 cm diameter, wrinkled, the margins irregularly lobed, the upper surface bluish-green, the lower surface white-woolly, the stalks at least half as long as the blades. Veins are sunken on upper surface and prominent underneath.
Flowers - White, 6 to 10 mm long, arranged densely around the stems in the leaf axils. Flowering occurs mainly in spring, sometimes through to autumn (September to March). | |
Seeds - Brown or black, ovoid or triangular, slightly roughened, 1 to 2 mm long, up to 4 per capsule.
Roots - Branched woody taproot or rootstock with numerous fibrous lateral roots.
The Problem
Horehound is a weed of pastures and crops in southern Australia where it thrives on poor soil and in waste places. It invades poor pastures which provide little competition. Horehound contains a bitter alkaloid which makes it unpalatable for grazing livestock. Horehound burrs contaminate wool, reducing the value of the fleece. The meat of animals which are forced to eat horehound is tainted by the plant's strong flavour, and it takes about 7 grazing days on clean pasture for animals to lose this.
There are reports of horehound causing stomach impaction in sheep and acting as an alternative host to pest insect species. As well as being an agricultural weed of pastures horehound has become an important environmental weed because of its ability to invade disturbed native vegetation.
Dispersal
Seeds are primarily dispersed by stock, as the fruit or burr readily attaches to wool, fur, clothing and similar materials. Water is also an effective dispersal agent, and horses are known to pass the seeds, after ingestion, in a viable condition.
Management Program
Some control methods described in this note are only effective if used in combination with other control options as part of a long-term management program.
If used in isolation, these methods do not effectively destroy the plant, allowing it to re-shoot or continue to grow. Authorised officers from DPI or DSE may direct landowners to undertake specific control activities to ensure methods are used that are capable of destroying plants and preventing their spread.
Where directed to do so, landowners must use the method or methods as directed by the authorised officer. In most cases the landowner will be able to choose from a variety of options appropriate for use in their particular situation.
The integration of a number of control techniques coupled with good pasture management is likely to give the best long-term control of horehound. Priorities for controlling different infestations must be worked out when planning a horehound management program. Clean areas should be kept free of horehound and managed in a way that will prevent infestation. Lightly infested areas should be cleaned up as soon as possible to prevent spread. Extensive infestations are best quarantined and tackled progressively as part of a pasture improvement program.
Cultivation
Horehound will not persist under cultivation. Hand-pull or hoe solitary plants before they set seed. | Figure 2. Horehound infestation. |
Pasture Management
Deep ploughing and a rotation of crops before establishment of new pasture will enhance control results.
Burning and Grazing
Some control on non-arable areas is achieved by burning to destroy old bushes and encourage seed germination, followed by heavy grazing with sheep to kill seedlings.
Chemical Control
The Australian Pesticides & Veterinary Medicine Authority (APVMA) is responsible for the assessment and registration of agricultural and veterinary chemicals in Australia. As chemical products are registered on a daily basis and renewal of these registrations are undertaken each financial year, there is much change in the registration status of products each year. The information is available from APVMA (external link).
The Chemical Standards Branch (CSB) of the Department of Primary Industries provides information on agricultural chemicals registered in Victoria and their uses. Enquiries will be referred through the Customer Service Centre on 136 186. Information can also be obtained by visiting the CSB website.
Under Victorian legislation there are controls on the use of agricultural chemicals. It is the responsibility of the user to be familiar with these controls. These responsibilities are outlined in Information Note AG0520: “Responsible use and handling of farm chemicals”.
Farm chemicals are registered for specific uses. Each chemical has a ‘product label’, which documents the approved use and the approved rate of use within each State of Australia. This label is important in determining the appropriateness of chemical use.
Choose only products registered for use on horehound in your particular situation. Read the product label carefully and follow all label instructions.
Your chemical retailers can provide information on registered chemical products that are available in their store. They can also supply a ‘material safety data sheet’ that outlines the health and safety issues associated with use of a product.
Legal use of some restricted chemicals requires the user to possess an Agricultural Chemical User Permit (ACUP). Other chemicals have restrictions on their use in Agricultural Chemical Control Areas (ACCAs).
Information on ACUPs, ACCAs and other chemical information can be found on the CSB website.
Biological Control
A biological control program commenced in 1990. The horehound plume moth, Pterophorus spilodactylus, was first released in 1994 and is now established at a number of localities in Victoria. It is specific to horehound and the caterpillar (larva) feeds on the growing tips of the plants and then work their way down the shoot, progressively defoliating the stem. This weakens the plant and reduces the number of seeds and flowers produced.
The horehound clearwing moth, Chamaesphecia mysiniformis, was first released in March 1997. Larvae feed on the growing tissue inside the roots and stems. This affects the flow of water and nutrients through the plant, weakens it, reduces growth and increases the likelihood of the plant dying. Additional biological control agents are under investigation.
The brightly coloured orange and black horehound bug, Agonoscelis rutila, a native insect often seen on horehound in great numbers, does not provide any worthwhile control.
Biological control is a long term program which is best used on large, chronic infestations with a low priority for control due to inaccessibility, remoteness or low threat of spread.
For more detailed information on biocontrol refer to Information Notes: LC0150 Horehound suppression using the horehound plume moth; and LC0162 Horehound suppression using the horehound clearwing moth.
Further Advice
- Contact your local landcare or friends group for further assistance and advice.
- Call the DPI/DSE Customer Service Centre on 136 186.
- Contact your local DPI Pest Management Officer for advice on local programs.
- Visit the DPI website
- Weeds Australia (external link)
Reference
Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious Weeds of Australia. Melbourne, Inkata Press.
Acknowledgements
Drafted by John Weiss; edited by Sue Darby, Keith Turnbull Research Institute (KTRI), 1996. Updated by Ross Williamson, KTRI, August 1997. Revised by Ian Faithfull, KTRI, February 1998. Updated by Melanie Martin, DPI, October 2006. Chemical information supplied by Chemical Standards Branch August 2006. Updated by Ryan Cooke, DPI, July 2007.
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.
|
