Parthenium weed (Parthenium hysterophorus) - South West NRM

w e e d s o f n a t i o n a l s i g n i f i c a n c e 

P a r t h e n i u m w e e d – 

P a r t h e n i u m h y s t e r o p h o r u s 

● Current ● Potential 

Parthenium weed (Parthenium hysterophorus) 

The problem 

Parthenium weed is a Weed of National 

Significance. It is regarded as one of the 

worst weeds in Australia because of its 

invasiveness, potential for spread, and 

economic and environmental impacts. 

Parthenium weed is a major problem in 

rangelands and summer cropping areas 

of Queensland. It has a serious impact 

on the pastoral industry, costing farmers 

and graziers in Queensland over $22 

million a year in reduced production and 

increased management costs. Some 

people suffer severe allergic reactions 

to the plant or its pollen; it can cause 

dermatitis, hay fever and asthma. 

Parthenium weed is toxic to cattle, 

and meat from livestock that eat the 

weed can be tainted. It also threatens 

biodiversity in the Einasleigh Uplands 

bioregion and native grasslands in the 

central highlands of Queensland. 

The weed 

Parthenium weed is native to the 

subtropics of North and South America. 

It is a fast-maturing annual (or, under 

certain conditions, a short-lived perennial) 

with a deep tap root and an erect stem 

that becomes woody with age. It may 

eventually reach a height of 2 m. Its leaves 

are pale green, branched and covered 

with soft fine hairs. The small white 

flowers (4 mm across) have five distinct 

corners and grow on the stem tips. Each 

flower produces four or five black wedgeshaped 

seeds that are 2 mm long with 

thin white scales. 

Its large and persistent soil seedbank, 

fast germination rate and ability to 

undergo dormancy make it well adapted 

to semi-arid environments. It also releases 

chemicals that inhibit the germination 

and growth of pasture grasses and 

other plants. 

Parthenium weed – Parthenium hysterophorus 

Key points 

• Parthenium weed can germinate, grow, 

mature and set seed in four weeks. 

• Parthenium weed is toxic to stock and contact 

with parthenium weed, particularly its pollen, 

can cause allergic reactions such as dermatitis, 

hay fever and asthma in people. 

• The best way to prevent an allergic reaction 

to parthenium weed is to avoid contact with 

it, especially breathing pollen from flowering 

plants. 

• Pay close attention to property hygiene. 

Weed seeds are spread very easily by vehicles, 

machinery, stock, grain and fodder. 

• Use mechanical, chemical and biological control 

and grazing to manage parthenium weed. 

Parthenium weed matures quickly and produces large quantities of seed (up to 100,000 seeds per plant). 

Photo: Larry K. Allain

2 

Growth calendar 

Jan 

Feb 

Mar 

Apr 

May 

Jun 

Jul 

Aug 

Sep 

Oct 

Nov 

Dec 

Flowering 

Seed formation 

Seed drop 

Plant death 

Germination 

General growth pattern 

Growth pattern under suitable conditions 

4 mm 

Parthenium weed can flower year round. 

Photo: Colin G. Wilson 


Parthenium weed normally germinates in spring and early summer, produces flowers 

and seed throughout its short life and dies in late autumn. However, with the right 

conditions (rain, available moisture, mild soil and air temperatures), parthenium weed 

can grow and produce flowers at any time of the year. In a good season, four or 

five generations may emerge. In summer, if plants are stressed (eg due to lack of 

water), parthenium weed can complete its life cycle in four weeks. Buried seeds 

have been found to last much longer than seed on the soil surface, and a significant 

proportion can still germinate after eight to ten years. 

How it spreads 

Parthenium weed can produce large 

quantities of seed, up to 100,000 per 

plant. More than 340 million parthenium 

weed seeds per hectare can be present 

in the surface soil, compared to 120,000 

native grass seeds. 

The seed is easily spread by vehicles, 

machinery and animals, and in pasture 

seed, stock feed and water. Most long 

distance spread is in produce, vehicles 

and farm machinery. It can also be 

spread by flooding and by animals. 

Parthenium weed was first discovered 

in Queensland in 1955. In a short time 

it spread from isolated outbreaks to 

establish core infestations across the 

Central Highlands of Queensland and 

into New South Wales and the 

Northern Territory. 

Where it grows 

In Queensland it grows best on alkaline, 

clay-loam to heavy black clay soils but 

tolerates a wide variety of soil types. It 

aggressively colonises areas with poor 

groundcover and exposed soil such as 

wastelands, roadsides and overgrazed 

pastures. It does not usually become 

established in undisturbed vegetation 

or vigorous pastures. Drought, and 

subsequent reduced pasture cover, create 

the ideal opportunity for parthenium 

weed to establish. Flooded country is 

also very prone to parthenium weed 

distribution and flooded pastures may 

need to be spelled from grazing to gain 

their competitive edge. 

Potential distribution 

Parthenium weed is best suited to areas 

with an annual summer rainfall greater 

than 500 mm. Based on climate suitability, 

it could potentially grow in all mainland 

states and territories. 

What to do about it 

Preventing spread into new 

areas 

Preventing the spread of parthenium 

weed is the most cost-effective 

management strategy. 

There is a high risk of spreading 

parthenium weed by the movement of 

vehicles, machinery, livestock, grain and 

other produce. Queensland has a number 

of washdown facilities and contractors 

are required to clean harvesters and other 

equipment before leaving the state. All 

harvesters are inspected as they cross the 

Queensland – New South Wales border. 

Parthenium weed infests more than eight 

million hectares of central Queensland 

with serious outbreaks in the south and 

north of the state. Outbreaks, many of 

which have been controlled, have been 

found throughout New South Wales as 

far south as the Victorian border. 

Parthenium weed can germinate, grow, mature and set seed in four weeks. 

Photo: Sheldon Navie 

150 mm 

W e e d M a n a g e m e n t 

G u i d e • P a r t h e n i u m w e e d – P a r t h e n i u m h y s t e r o p h o r u s

3 

Property hygiene is also important. 

Double-check machinery (including the 

interior of the vehicle) moving onto your 

property and drive visitors around in your 

own vehicle. Always wash down vehicles 

and machinery in the same area to allow 

easy follow-up control of any seeds that 

may germinate. Ensure that service 

provider vehicles (eg telephone, electricity, 

gas) are free of parthenium weed seed. 

Avoid moving cattle in wet weather as 

they readily transport seed in muddy 

soil. When new stock arrive on a 

property, hold them in yards or small 

paddocks to let seed drop from their 

coats and tails before releasing them 

into large paddocks. Always feed stock 

in the same area to contain weeds 

imported in contaminated fodder. 

When you are buying hay or seed, be 

aware of what you are buying. In Queensland 

landowners are required to supply 

a vendor declaration to state whether 

their produce is free of parthenium. 

Recent experience with 

parthenium weed 

The Queensland Department of Natural 

Resources and Mines and the Parthenium 

Action Group have developed 

management and control techniques 

for parthenium weed, which include 

a combination of biological control 

agents, pasture management, cultivation 

and herbicides. Small infestations can 

be eradicated by early detection and 

monitoring. An ongoing commitment 

is needed to remove any seedlings and 

ensure new infestations do not establish. 

The extent of parthenium weed in New 

South Wales has been significantly reduced 

in recent years; all known roadside 

infestations have been suppressed and 

all known infestations on private land 

are under active control. In the Northern 

Territory, parthenium weed has been 

eradicated from previous infestations on 

the Roper River, at Katherine and in the 

Gulf of Carpentaria. However, although 

the area infested with parthenium weed 

is being reduced, the number of new 

infestations is increasing. 

Large parthenium weed infestation in central Qld. 

Photo: Qld DNRM 

Control of new outbreaks 

Once parthenium weed has been 

positively identified, treat isolated 

patches immediately with herbicides 

recommended by the local council weeds 

officer. Watch the area closely for at least 

seven years as repeated spraying may 

be necessary to kill new germinations. 

Don’t pull up plants by hand, particularly 

if they have already set seed. There is 

a danger that mature seeds will drop 

off the plant and increase the area 

of infestation. 

Control in pasture... 

Control in pasture requires timely 

herbicide application and pasture 

management. Conservative stocking 

to keep a good pasture cover is the 

best way of controlling large-scale 

parthenium weed infestations and 

preventing new infestations in clean 

areas. Areas where stock congregate, 

such as watering points, often have 

low groundcover and are highly 

susceptible to parthenium infestation. 

To overcome this problem, establish 

several stock water points per paddock 

and rotate stock between them. 

Breaking up large paddocks by fencing 

into single units of similar land type can 

even out grazing and thus avoid bare 

patches where weeds can invade. 

It also allows more flexible management 

60 mm 

Parthenium weed’s large and persistent soil 

seedbank and fast germination rate make 

it well adapted to semi-arid environments. 

Photo: Colin G. Wilson 

strategies, such as spelling pasture and 

applying herbicide. 

...and control in crops 

Parthenium weed is becoming a 

significant problem in crops due to the 

threat to exports from contaminated 

grain or other produce. Once in a crop 

it is very difficult to eradicate, so try to 

keep crops clean by spraying selective, 

pre-emergent herbicides where possible 

and cleaning equipment and machinery 

such as harvesters. Do not purchase seed 

that does not comply with the relevant 

seed Acts. For further information on 

parthenium weed control in crops, consult 

your local crop agronomist. 

Herbicides 

Timing of chemical control is critical. 

Parthenium weed should be treated 

when plants are small and have not 

produced seed, and when grasses are 

actively growing to recolonise the 

infested area (eg early summer). 

Maintaining competition is important 

for control of parthenium weed, so 

spraying with a selective herbicide that 

will not kill other species is recommended. 

Keep a close watch on treated areas 

for at least seven years and spot spray 

isolated outbreaks. A number of 

herbicides are recommended for 

parthenium weed control. Contact 

your local authority for details. 



4 

Weed control contacts 

State / 

Territory 

Department 

Phone 

Email 

Website 

ACT 

Environment ACT 

(02) 6207 9777 

EnvironmentACT@act.gov.au 

www.environment.act.gov.au 

NSW 

NSW Agriculture 

1800 680 244 

weeds@agric.nsw.gov.au 

www.agric.nsw.gov.au 

NT 

Dept of Natural Resources, 

Environment and the Arts 

(08) 8999 4567 

weedinfo.nreta@nt.gov.au 

www.nt.gov.au 

Qld 

Dept of Natural Resources and Mines 

(07) 3896 3111 

enquiries@nrm.qld.gov.au 

www.nrm.qld.gov.au 

SA 

Dept of Water, Land and 

Biodiversity Conservation 

(08) 8303 9500 

apc@saugov.sa.gov.au 

www.dwlbc.sa.gov.au 

Vic 

Dept of Primary Industries/Dept 

of Sustainability and Environment 

136 186 

customer.service@dpi.vic.gov.au 

www.dpi.vic.gov.au 

www.dse.vic.gov.au 

WA 

Dept of Agriculture 

(08) 9368 3333 

enquiries@agric.wa.gov.au 

www.agric.wa.gov.au 

Australia wide 

Mechanical removal 

Ploughing the weed in before plants reach 

flowering stage and then establishing 

pasture may be effective. Before crops 

are planted, parthenium weed is normally 

ploughed in, or pre-emergent herbicides 

can be used. 

Biological control 

Australian Pesticides and Veterinary 

Medicines Authority 

Biological control of parthenium weed 

has been investigated in Australia for 

more than 20 years. Nine insect species 

and two rusts have been released. Most 

insects and both rusts have established. 

(02) 6272 5852 

contact@apvma.gov.au 

Listronotus setosipennis, which is having 

limited success; a seed-feeding weevil, 

Smicronyx lutulentus, which lays eggs 

in the flower buds, leaving the newly 

hatched grubs to feed on the seed heads; 

a leaf mining moth, Bucculatrix 

parthenica, from Mexico, whose grubs 

feed on the leaves of parthenium weed; 

a stem-galling weevil, Conotrachelus 

albocinereus, from Argentina, which is 

still becoming established; and Carmentia 

ithacae, a stem boring moth from Mexico 

released from quarantine in 1999 and 

still becoming established in the 

Central Highlands. 

www.apvma.gov.au 

For up-to-date information on which herbicides are registered to control parthenium weed and the best application methods and dosages, contact your state or 

territory weed management agency or local council. This information varies from state to state and from time to time. Contact details are listed above, including 

contacts for the Australian Pesticides and Veterinary Medicines Authority, which hosts the PUBCRIS database. This database contains information on all herbicides 

that are registered for use on weeds in each Australian state and territory. 

When using herbicides always read the label and follow instructions carefully. Particular care should be taken when using herbicides near waterways 

because rainfall running off the land into waterways can carry herbicides with it. Permits from state or territory Environment Protection Authorities 

may be required if herbicides are to be sprayed on riverbanks. 

when insect populations are reduced 

and need time to recover. 

Puccinia abrupta, a winter rust from 

Mexico, infects and damages leaves and 

stems. It is established over a wide area 

in Queensland, south from Clermont. The 

release program for a second rust, Puccinia 

melampodii, a summer rust, began in 

1999 and is continuing. Its establishment 

has been hindered by drought but further 

releases have been made in some areas 

following better rainfall. Its impact is 

expected to improve if rainfall increases 


Biological control is one tool that forms 

part of an integrated management 

program for large-scale scattered and 

dense infestations. However, biological 

control on its own will not eradicate 

parthenium weed infestations. 

The leaf beetle Zygogramma bicolorata 

and the stem moth Epiblema strenuana 

cause the most damage. The beetle 

emerges in late spring and is active until 

autumn. The moth is established in all 

parthenium weed areas. Its larvae (grubs) 

feed inside the stem, stunting the plant’s 

growth and reducing its competitiveness 

and seed production. Other species are: 

a stem boring weevil from Argentina, 

Seasonal conditions and the need for 

green plants for insect survival play a 

major role in the effectiveness and 

abundance of biological control agents. 

This is highlighted during long dry periods 

6 mm 

The leaf beetle Zygogramma bicolorata emerges 

in late spring and is active until autumn. 

Photo: Rachel McFadyen 

40 mm 

The leaf beetle Zygogramma bicolorata can remove 

virtually all of parthenium weed’s foliage. 




5 


in the areas infested with parthenium 

weed. The rust weakens the plant by 

damaging the leaves over the summer 

growing season. 

Field collection and distribution of 

biological control agents will help reduce 

local parthenium weed infestations. For 

best results a nursery site to raise biological 

control agents should be developed. 

Good nursery sites can be as simple as 

a leaking pipe or tank. Other ideal sites 

are infested black soil creek flats, gullies 

or swampy areas. At the same time, 

ensure that your nursery site does not 

become a source for further parthenium 

30 mm 

The distinctive branched leaves are covered 

with soft, fine hairs. 

Photo: Sheldon Navie 

weed infestations. Contact your state/ 

territory weed management agency or 

local council for assistance in collecting 

and rearing biological control agents 

for parthenium weed. 

Burning 

Burning is not a useful control strategy 

for parthenium. However, research 

suggests that burning for other purposes 

(eg woody weed control) will not result 

in an increased infestation of parthenium 

so long as the pasture is allowed to 

recover before stock are introduced. 

Stocking of recently burnt areas known 

or suspected to contain parthenium weed 

decreases competition, ultimately creating 

a more serious infestation. Permits may 

be required to burn, so check with your 

state/territory weed management 

agency or local council. 

Legislation 

Parthenium weed is declared a noxious 

weed in all mainland states and territories, 

and landowners are required to control it. 

Its introduction into Australia is prohibited. 

Legislation introduced into Queensland 

recently makes it a legal requirement 

for suppliers of stock, machinery, soil, 

water or other products likely to transport 

weed seeds to complete a declaration 

stating whether or not the material is 

clean of parthenium weed. In New 

South Wales landowners must report 

the presence of parthenium weed to the 

local control authority within three days. 

This agency will then advise the necessary 

action to be taken to eradicate the 

infestation. 

Acknowledgments 

Information and guide revision: Darren 

Moor (Qld DNRM), Gail Godwin Smith 

(Parthenium Action Group) and other 

members, Rachel McFadyen (Weeds CRC), 

Richard Carter (NSW Agriculture/Weeds 

CRC), Sheldon Navie (University of 

Queensland), Dhileepan Kunjithapatham 

(Qld DNRM) and John Thorp (National 

Weeds Management Facilitator). 

Maps: Australian Weeds Committee. 

...case study 

Management of parthenium weed at Mt Panorama 

While parthenium weed is certainly 

something landholders should try and 

prevent invading their properties, it can 

be managed. This is the message from 

Gail Godwin Smith, project officer with 

the Parthenium Action Group. Gail and 

her husband Howard Smith are farmers 

and graziers at Rolleston in central 

Queensland. 

However, changing management 

practices has been the major factor in 

controlling parthenium, says Gail. The 

main infestations on the property now 

occur along waterways. Many of these 

waterways have been fenced off to 

allow native vegetation to compete 

with parthenium and they are grazed 

seasonally to reduce any fire risk. 

weed, and so they must live with it and 

manage it appropriately. 

In 1988, when Howard and his family Favourable seasonal conditions allow 

bought ‘Mt Panorama’, it was infested spelling of paddocks and rotation of cattle 

with parthenium weed. Today, they regard so that healthy pasture is maintained 

the weed as an indicator species which and no one paddock gets eaten out. 

appears if pasture is being overgrazed. 

Parthenium weed is no longer a problem 

‘Mt Panorama’ has been a trial property on the cultivated country either, where 

for the release of biological control agents, 

case study 

two of which (the Zygogramma beetle 

and summer rust) have had a big impact 

on the weed. 

minimum tillage is used and pre-emergent 

herbicide sprayed for other weeds. 

The Smith family recognise that they are 

unlikely to totally eradicate parthenium 

Changing management practices has been the 

major factor in controlling parthenium weed 

on ‘Mt Panorama’. 

Photo: Qld DNRM 



Q u i c k r e f e r e n c e g u i d e 


Prevention 

Maintaining good hygiene on your 

property can prevent the spread of 

parthenium weed seed – check vehicles 

and machinery moving onto the 

property, drive visitors around in your own 

vehicle and always wash down vehicles 

and machinery in the same place. 

Always feed stock in the same area to 

contain weeds carried in contaminated 

fodder and place new stock into a 

small holding paddock until seed has 

dropped from their coats and tails. 

New outbreaks 

Treat immediately with a herbicide 

recommended by the local council 

weeds officer. Apply herbicides when 

plants are actively growing and before 

they set seed; keep a close watch on 

treated areas for at least seven years. 

Spot spray one to two weeks after 

rain, when plants are large enough 

to see but before they produce seed. 

In pasture 

10 mm 

The stem moth, Epiblema strenuana, is 

established in all parthenium weed areas. 


Stock conservatively to keep a good 

pasture cover, which will help prevent 

invasions of parthenium weed. Some 

strategies to improve pasture competition 

are to: spell pastures in the growing 

season, use rotational grazing, and 

spray herbicide to encourage grass 

seed production and reseeding. 

To overcome high grazing pressure 

points, establish several stock water 

points per paddock and rotate stock 

between them. 

Fencing different land types enables 

better grazing management. 

In crops 

Keep crops free of parthenium weed by 

spraying selective, pre-emergent herbicides 

where possible and cleaning equipment 

and machinery such as harvesters. 

Biological control 

Researchers in Queensland have 

located and tested a number of 

biological control agents against 

parthenium weed. Landowners can 

collect and distribute biological control 

agents to help reduce local infestations. 

Control options 

Type of infestation 

Chemical 

Biological 

Physical 

Pasture 

management 

Mechanical 

Light – few plants, 

over a small area 

Medium – plants over 

a medium area 

Heavy – large 

number of plants 

Spot spray before 

seeds set. 

Spray before 

seeds set. 

Spray before 

seeds set. 

Not suitable. 

Release biological 

control agents. 

Establish a nursery site 

for biological control 

agents if possible. 

Hand pulling is 

not recommended 

because of the health 

risks associated with 

parthenium weed. 

Use strategic fencing 

to separate different 

land types and 

improve grazing 

management. 

Maintain good 

pasture cover by 

not overgrazing. 

Some landholders have 

achieved success by 

ploughing in 

parthenium weed 

in the rosette stage 

before it seeds, but 

this must be followed 

up by sowing a crop 

or direct seeding 

perennial pasture. 

© 2003 Information which appears in this guide may be reproduced without written permission provided the source of the information is acknowledged. 

Printed in Australia on 100% recycled paper. 

ISBN 1-920932-12-7 

Disclaimer 

While every care is taken to ensure the accuracy of the information in this publication, the CRC for Australian Weed Management and the Commonwealth Department of the Environment 

and Heritage take no responsibility for its contents, nor for any loss, damage or consequence for any person or body relying on the information, or any error or omission in this publication.

Parthenium weed (Parthenium hysterophorus) - South West NRM

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