Hemlock

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Hemlock	LC0138
Department of Primary Industries Updated: August 2007 To view the Adobe Acrobat file, you will need the Adobe Acrobat Reader (external link).	(PDF 218kb)

Common and Scientific Names

Hemlock, carrot fern
Conium maclatum L.

Origin and Distribution

Hemlock is a biennial or occasionally an annual plant which originated in Europe, western Asia and North Africa and was deliberately introduced to Australia. It prefers moist, neglected situations and can be found in most areas of Victoria. It is usually unimportant as an agricultural weed but sometimes invades pastures and areas of cultivation. As an environmental weed it has invaded lowland grassland and grassy woodland, riparian vegetation and warm temperate rainforest.

Description

Hemlock reproduces from seeds which usually germinate in autumn. Annual plants flower in the first spring, produce seeds and die in summer. Biennial plants remain in a vegetative state until their second spring, flower, then set seed and die in their second summer.

Stems - Erect, up to 3 m high but often less than 2 metres; strong, hairless, hollow except at nodes, longitudinally grooved; pale green, blotched with purple and emitting an offensive odour when damaged.

Leaves - Fern- or carrot-like, 12 to 25 cm long but up to 50 cm, hairless, alternate, emitting a strong, acrid (‘mousey’) odour when crushed. Leaf stalks are deeply cupped at the base and surround the stem.

Flowers - White or greenish-white, 2 to 4 mm diameter with five petals; numerous, in dense umbrella-like clusters at the ends of the stems. Present in spring to early summer.

Seeds - Dark-grey to brown, 3 mm long, globular with five prominent wavy ridges.

Roots - Long white taproot which may be branched.

The Problem

Hemlock contains five toxic alkaloids which vary in concentration due to climatic conditions. The fruit, vegetative parts and roots are all poisonous to humans and stock. The Greek philospher Socrates is said to have been killed with hemlock. In Victoria a child died from hemlock poisoning in 1994. Handling the plant can cause dermatitis in some people.

Cattle, pigs, horses and poultry are more susceptible to hemlock poisoning than sheep and goats. The plant is rarely grazed when green and is more likely to be consumed in hay, chaff or silage. Symptoms of hemlock poisoning in stock include dullness, loss of muscular power, stumbling and falling, nausea, dilation of pupils and complete paralysis. Symptoms may show as quickly as 12 minutes after the plant is eaten and death may occur in 2 to 3 hours.

Hemlock grows rapidly after autumn rains, and on disturbed soils can exclude most other vegetation. It does not readily invade well managed established pastures.

Dispersal

Seeds can be spread by animals, machinery, water, agricultural produce including hay and silage, gravel, soil extraction and to a limited extent by wind.

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.

Figure 1. Hemlock flowers.

Figure 2. Hemlock infestation.

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.

A management program must be initiated in order to effectively control hemlock. Integrated management strategies should be used to control different levels of infestation. Clean areas should be managed to prevent infestation. Lightly infested areas are best treated quickly to prevent spread. Extensive infestations should be quarantined and progressively controlled over time.

Cultivation
Hemlock does not persist under cultivation. Affected pastures should be disc-ploughed before the weed flowers and topdressed to encourage a vigourous pasture sward. Several cultivation treatments may be necessary for large areas. The danger of damage to soil structure and soil erosion should be considered.

Hand Pulling, Hoeing, Slashing
Individual plants and localised patches should be hand pulled or hoed before flowering. When hand pulling hemlock, heavy rubber gloves should be worn to prevent contamination from plant toxins. Slashing just prior to flowering may provide effective control ,but sometimes new growth is produced, requiring further treatment.

Pasture Management
Sound pasture management, which ensures ground cover is maintained, will prevent establishment of hemlock.

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 Agriculture 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 hemlock 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 at the CSB website.

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 Catchment Management Officer for advice on local programs.
Visit the DPI website
Weeds Australia (external link)

References

McBarron, E.J. (1983) Poisonous Plants Handbook for Farmers and Graziers. Melbourne, Inkata Press.

Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious Weeds of Australia. Melbourne, Inkata Press

Acknowledgments

Prepared by Ross Williamson, 1997. Updated by Ian Faithfull, April 1998. Updated by Melanie Martin, DPI, October 2006. Chemical information supplied by Chemical Standards Branch August 2006. Updated by Adam Kay, DPI, August 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.

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