weeds of national significance

Mimosa – pigra

Current Potential

Mimosa (Mimosa pigra) The problem

Mimosa is a Weed of National Significance. It is regarded as one of the worst weeds in because of its invasiveness, potential for spread, and economic and environmental impacts.

Mimosa forms dense stands that replace all native vegetation on the ecologically Mimosa and economically valuable wetlands of the Top End of northern Australia.

Mimosa invasion threatens the production, – Mimosa pigra cultural and conservation values of wetlands, and reduces the scope for exploitation of resources by land users. Pastoralists are affected because the inedible and thorny mimosa smothers Mimosa invading wetlands on the Adelaide River floodplain, NT. and replaces grasslands, blocks access Photo: Colin G. Wilson to stock watering points and hinders mustering. Additionally, the harvesting the matures. The fernlike green Key points of bush foods by indigenous people is , which fold together at night or hampered by mimosa. when touched, are made up of many • Preventing the spread of mimosa is essential in protecting northern wetlands. In environmental terms, nationally and fine leaflets and occur in pairs along internationally significant wetlands are branches. Larger thorns (5–10 mm long) • Once established, mimosa is very difficult threatened by mimosa, which reduces are found on the stem, with smaller to control. the biodiversity of plant and animal life thorns on branches between leaves. • Prevent mimosa spread by using effective on the floodplains by outcompeting Round flower heads (10–20 mm in quarantine, hygiene and monitoring, and native and reducing available diameter) are composed of 100 pink– by controlling feral animals. habitat for animals. mauve individual flowers. Each flower • Control mimosa in small patches before it seeds by hand pulling, bulldozing or spraying Although currently limited in distribution, head produces between 10 and 20 olive- herbicides. if left unchecked mimosa has the potential green seed pods, 60–80 mm long, which to dominate wetlands across the whole turn brown and break into segments • Larger infestations should be sprayed from the of northern Australia. when mature. Each segment contains air. Follow-up will be required. an oblong-shaped seed, 4–6 mm long • Biological control agents (eg moths and weevils) The weed and 2 mm wide. The seed segments, also help to control mimosa in the long term. which are covered with many fine hairs, Mimosa is a branched prickly , float on water and adhere to clothing growing up to 6 m. The stem is greenish or hair. The root is a branching taproot, in young plants but becomes woody as reaching to between 1 and 2 m depth. 2

Growth calendar 15 mm Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Flowering Pod formation Seed drop

General growth pattern Growth pattern in wet years

Mimosa can germinate year round if the soil is moist but not flooded. However, most germination takes place at the start and end of the wet season. Growth in seedlings is rapid, and flowering occurs between 4 and 12 months after germination. Mimosa mainly flowers during the wet season. The main flowering season is January–March but flowering can be extended into Photo: Colin G. Wilson the dry season under moist conditions. Seeding occurs approximately five weeks after flowering and fruits ripen after about three months. Most seeds germinate when first wetted although a tough, impermeable coating allows some seeds to seeds was removed from the Adelaide remain viable in sandy soil for over 20 years. Mimosa grows extremely quickly, and River in the 1950s and used around in ideal conditions infestations double in size every 18 months. the Top End in commercial building operations. Mimosa has since spread to some of the main river systems (Finniss, hygiene measures (ie washdowns, How it spreads Reynolds, Mary, Daly, East Alligator and inspections) should be used after South Alligator) in the Top End. It is now Mimosa mainly reproduces via seeds. contact with mimosa. Non-essential present as far as the Victoria River in the Large plants can produce vast amounts activities should not be conducted in west and the Phelp River (in Arnhem of seeds, up to 220,000 per year. mimosa patches to limit the likelihood Land) in the east. A mimosa outbreak Mimosa seeds are typically dispersed in of spread. was discovered near Proserpine in two main ways: carried downstream

– Mimosa pigra Mimosa was first brought into the northern Queensland in February 2001. during flooding or transported by Northern Territory to the Darwin Botanic animals or machinery. Animals can Gardens around 1891. Its spread around spread seeds in their droppings (eg Where it grows Darwin over the next 60 years was not Mimosa cattle, horses) or in mud attached to particularly conspicuous, until a large Wet places in the humid and sub-humid their bodies (eg kangaroos, pigs, infestation was discovered in 1952 at tropics are the most ideal habitats for buffalo). Humans transport seed Adelaide River, 100 km south of Darwin. mimosa. It occurs along roadsides, attached to their clothing or It was then correctly identified as Mimosa watercourses and seasonally inundated equipment (eg boats, cars, tractors) pigra, and its invasive tendencies were wetlands. It is found on a wide variety after contact with an infestation. revealed as it spread downstream. It is of soils and is tolerant of flooding. Therefore, appropriate care and routine believed that sand contaminated with Mimosa is native to tropical America but is now a serious weed in , , South-East Asia and some Pacific islands. 60 mm It occurs on wetlands across northern Australia, occupying about 85,000 ha of the Top End.

Potential distribution

Much of northern Australia is climatically suited to mimosa. The infestation at Proserpine, which is outside of its projected distribution, indicates that it may actually Ripe mimosa seed pods ready to drop at Finniss River, NT, in July. be able to survive further south than its Photo: Colin G. WIlson potential distribution suggests.

Weed Management Guide • Mimosa – Mimosa pigra 3

What to do about it

The spread of mimosa must be prevented by careful management

Preventing its introduction is the most cost-effective strategy in dealing with mimosa. Its main weedy attributes – an 40 mm invasive nature, vigorous growth rate, Mimosa is also called the giant sensitive plant, because its leaves constrict when touched (right). Photo: Colin G. Wilson high fertility and durable seeds – make control difficult and expensive. Reducing the spread of mimosa requires careful Report new occurrences of mimosa to variety of effective herbicides that can management of infestations. Soil or sand the relevant local council or state or also be used to eradicate new or small (which could contain mimosa seeds) territory government agency. outbreaks. For smaller infestations should not be removed from infested spraying the entire plant from a back- areas. Any transport vehicle or machinery Control mimosa with pack sprayer with an appropriate, used in infested areas should be thoroughly integrated weed management registered herbicide will kill mimosa if cleaned before moving to other areas. applied correctly. All treated plant material Recent research and field experience should be burnt to ensure it does not Also, stock from infested areas should in the Northern Territory indicates that regrow, and these sites should be checked be held for at least eight days to allow mimosa can be managed through regularly for new plants over a number all ingested seeds to be expelled, and careful and systematic control efforts. of years. the holding pen must be monitored for An integrated approach using several mimosa. Existing infestations should be weed management techniques is the monitored and feral animals, which are most effective way to deal with dense Larger infestations should be attacked with chemical control known to transport seeds and create infestations of mimosa. However, the conditions suitable for germination, characteristics of the infestation (eg size, The integrated approach to large should be controlled. density, location, position within the infestations of mimosa commences with catchment) and the availability of resources treatment with a registered herbicide, If mimosa is introduced into an area, will determine the most appropriate most effectively with an aerial application. then prevention of spread is the next course that control should take. Early morning application is most effective highest priority. Mapping, planning and because of higher humidity, which allows allocation of sufficient resources are Small outbreaks can be better delivery of the herbicide to the essential management tools. The spread controlled with physical/ plants and better uptake by the leaves. of mimosa in the monsoon season due mechanical and/or chemical Although aerial spraying kills adult trees, to floodwaters can be restricted by control it is expensive and regrowth of germinated retaining vegetation cover, which impedes Single plants or small outbreaks of seeds can be prolific. Up to five years seed movement. Vegetation cover is mimosa can be removed by hand pulling of spraying is likely to be required on best managed by controlled stocking or grubbing, ensuring that as many roots severe infestations. and judicious use of fire. as possible are removed. There are a Granular herbicides target roots and should be placed near mimosa bushes before rain is likely to occur. However, the effectiveness of root-absorbed herbicides varies with soil and land types. Consult your state or territory government agency to determine the most appropriate herbicide for your local conditions. Although residual herbicides provide some protection from future germination of mimosa seeds, the growth of other preferred trees and Community control of mimosa at Black Jungle, near Darwin, NT. will also be inhibited if their Photo: Colin G. Wilson roots encroach into the treated area.

Weed Management Guide • Mimosa – Mimosa pigra 4

Weed control contacts

State / Department Phone Email Website Territory NT Dept of Infrastructure, Planning (08) 8999 5511 [email protected] www.nt.gov.au and Environment Qld Dept of Natural Resources and Mines (07) 3896 3111 [email protected] www.nrm.qld.gov.au WA Dept of Agriculture (08) 9368 3333 [email protected] www.agric.wa.gov.au

Australia wide Australian Pesticides and Veterinary (02) 6272 5852 [email protected] www.apvma.gov.au Medicines Authority

For up-to-date information on which herbicides are registered to control mimosa 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 or directly onto the water.

treatments or will readily re-establish themselves in treated areas.

All parts of the plant – the seeds, flowers,

15 mm leaves, tips, branches and roots – have been targeted with at least one biological control species. So far, 13 agents (insects Mimosa and fungi) have been released. This work is part of the Northern Territory Government / CSIRO joint project – Mimosa pigra ’Biological control of Mimosa pigra and Adult moths mating on a Controlling large stands with bulldozers and fire. mimosa stem. The grubs tunnel into the stems. integration with other control options’, Photo: NT Government Photo: Colin G. Wilson funded by the Commonwealth Government’s Natural Heritage Trust. Four of these species have become control if native species will be affected Larger infestations – effective in controlling mimosa by – check with your local council or state mechanical follow-ups and reducing seed production and the size or territory weed management agency. strategic use of fire of the seedbank, and occasionally killing Rolling, raking or back-ploughing dead Following herbicide treatment, dead adult plants. The most successful insects mimosa also assists in its removal. mimosa stems should be mechanically are those that can feed on mimosa all Mechanical clearing could also be used cleared and burnt. Chaining is a common year round, notably stem miners. prior to herbicide application to improve clearing method in which two bulldozers accessibility to large infestations. Sites In the long term biocontrol on its own pull a heavy chain between plants. will require regular follow-up monitoring, offers the only cost-effective control Burning is an inexpensive way of clearing similar to a ‘search and destroy’ approach option for treating very large infestations debris, improving access and killing used in Kakadu National Park (see case of mimosa because of the high costs surface seeds or at least breaking the study). of chemicals, machinery and labour. dormancy stage. However, the present biocontrol agents Sufficiently hot fires can kill mature Release biological control are very slow acting and may provide mimosa or at least damage it so that agents at the start of effective control only after several decades. follow-up control treatment is more treatment If more rapid treatment is required, biocontrol should be used in conjunction effective. The outer edge of a mimosa Biological control can be initiated at any with mechanical and chemical methods stand is first killed with herbicides and stage of the overall process. Best results then crushed by a bulldozer. When the will be obtained when biocontrol agents as part of an integrated management dead mimosa is burned under warm, are released at the commencement of plan. Biocontrol agents are very effective windy conditions, the entire infestation mimosa control because these agents in attacking mimosa regrowth and can be destroyed. Permits may be required require a long time to be effective. Bio- seedlings in areas that have been to light fires or conduct mechanical control agents will survive other control already treated.

Weed Management Guide • Mimosa – Mimosa pigra 5

The ‘search and destroy’ mission for mimosa in Kakadu...case National Parkstudy

Parks Australia North and its predecessors plants and hand pulling to remove will be an ongoing problem for the park, have adopted a zero tolerance for mimosa seedlings. If a seeding plant is discovered, because mimosa is present on both the within Kakadu National Park. They use any seed that can be recovered is collected eastern and western borders of Kakadu. a ‘search and destroy’ approach to and later incinerated, and the ground is Additionally, even after 22 years, new mimosa combined with regular (three burnt using fuel to try to kill any seed seedlings are still emerging from old times a year) monitoring of 260 plots mixed into the soil. In addition to treating plots, indicating that the seed remains on floodplains that have previously mimosa infestations, feral animals (eg viable for at least this time period. Even contained mimosa. pigs and buffalo) that spread mimosa with such a dedicated and costly effort are controlled by shooting. Every visit to control mimosa, the number of new Four full-time staff use a variety of to every plot is recorded on a database. infestations found every year remains transportation (air boats, quad bikes, fairly constant. 4WDs) to monitor nearly 10,000 square Presently, there are no known large kilometres, at a total annual cost of infestations of mimosa in Kakadu National The complete eradication of mimosa in approximately $500,000. This is Park, a far cry from when mimosa control Kakadu National Park is therefore a long- equivalent to just over $2 per hectare. commenced 22 years ago by fencing term program, which is crucial to the off and chemically treating several large maintenance of the World Heritage Rangers use herbicides (both spraying infestations. However, it is clear that this wetlands of Kakadu. and soil application) to control adult case study

should include some form of mechanical and chemical control. Biological methods will aid the successful control of larger infestations. The site should be checked on an ongoing basis to ensure that any

– Mimosa pigra viable seeds remaining in the seedbank have not germinated. As the Kakadu example shows, constant vigilance is required. Mimosa

Legislation

Landholders are required by law to control Mimosa stands outcompete virtually all other forms of vegetation. Photo: Colin G. Wilson mimosa where it occurs in the Northern Territory and Queensland. In parts of the Northern Territory where eradication is Revegetation can reduce not be overgrazed because this can help not feasible, its spread must be controlled. mimosa regrowth promote the growth of weeds, like The introduction of mimosa is banned mimosa, that are not grazed by stock. in Western Australia. Revegetation is the final stage of the integrated management cycle. If Repeats, follow-up and necessary a native pasture grass which Acknowledgments monitoring to keep on can outcompete mimosa, such as native top of mimosa Information and guide revision: hymenachne (Hymenachne acutigluma), Quentin Paynter (CSIRO/Weeds CRC), could be sown at the site. However, do Note that the integrated management Steve Wingrave (NT DIPE), Blair Grace not revegetate with olive hymenachne of mimosa is a cyclical process and may (NT DIPE/Weeds CRC), Tim Heard (CSIRO/ (Hymenachne amplexicaulis), which is require many repeats of the cycle before Weeds CRC), Simon O’Connor (Kakadu a weedy pasture grass that invades the weed is controlled. Aerial spraying National Park) and John Thorp (National wetlands. Sowing the native grass will may need to be repeated several times, Weeds Management Facilitator). help reduce the numbers and growth and then followed up by a coordinated rate of mimosa seedlings. Pastures should long-term ground-based program that Maps: Australian Weeds Committee.

Weed Management Guide • Mimosa – Mimosa pigra Quick reference guide

For small outbreaks... Using fire mechanical and burning treatments, and ensure biocontrol agents are still Very small outbreaks of mimosa (only a Burning of chemically or mechanically present, until mimosa is eliminated or few plants) can be controlled by removing treated stands will also help with mimosa can be effectively managed. plants by hand, making sure as many control by further stressing live plants, roots as possible are removed. Herbicides improving access and breaking seed can also be sprayed all over the plant. dormancy, but may also stimulate Small infestations should be revisited seedling germination. Therefore, annually to ensure there is no regrowth. follow-up control action will be required. Biological methods are ...and for large particularly effective in controlling regrowth and seedlings at this stage. Larger infestations require a more comprehensive approach, and may Revegetation involve three or four different techniques used together. When no other methods Fast growing grasses can help reduce of control are available, a slow but the spread of seed by floodwaters and inexpensive way to control mimosa is prevent the establishment and growth through the use of biological control of mimosa seedlings. Pasture grasses agents – introduced insects which should be sown where necessary and – Mimosa pigra attack mimosa and its seeds. not overgrazed.

For faster control combine biological control with the aerial application of Follow-up Mimosa herbicide, followed by the mechanical Follow-up control must be undertaken Infestation in the Adelaide River, NT, in April. clearing (by chaining) of treated mimosa. on all mimosa stands. Repeat the chemical, Photo: Colin G. Wilson

Control options

Type of infestation Biological Chemical Mechanical Physical Small Not suitable. Spot spraying by hand Not suitable. Hand grubbing (remove (few plants, small area) with registered herbicide. roots and burn plant). Medium Release of biological Spot spraying by hand Chaining, rolling, raking or Follow-up control (medium density, control agents. with registered herbicide. back-ploughing, then burning. of seedlings – could medium total area) include physical removal. Large Step 1. Release of Step 2. Aerial spraying Step 3. Attack with chaining, Follow-up control of (many plants, many ha) biological control with registered herbicide. rolling or raking. Use fire to kill seedlings – could include agents. any regrowth and break seed physical removal. dormancy. Go to step 2 if necessary.

© 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 1-920932-10-0

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.