Chapter 4. Case studies - Department of Land Resource ...

CHAPTER 4Case studies4. CASE STUDIES41

4.1 Case Study 1Kakadu National Park, NTTwenty-five years ago,Mimosa pigra began to spread throughoutthe floodplain and coastal areas of the Worldheritagelisted Kakadu National Park. Now,thanks to an ongoing control program, mimosais restricted to small outbreaks within the Park.Kakadu National Park is located approximately150km east of Darwin and forms part of theAlligator River region which flows into Van DiemenGulf. The park contains three major environments;the plateau and escarpment, savanna lowlands andfloodplains. Floodplains and coastal plains coverapproximately 215,000ha of the park.Kakadu is listed as a World Heritage area forits cultural and conservation value. Kakadu’swetlands are also recognised as internationallysignificant under the Ramsar Convention.The wetlands of Kakadu are an iconic touristdestination and provide dry season refuge fora prolific and diverse amount of wildlife. Thewetlands include many important cultural sites,fishing and hunting areas for the traditionalowners, the Bininj.The ability of mimosa to rapidly take over wetlandsthreatens the habitat of waterbird species such asthe magpie geese. Mimosa can also take over keyAboriginal hunting grounds for turtles and geese,as well as prevent access to fishing areas.In recognition of the threat mimosa posed tothe biodiversity and cultural values of the park, astrategy of ‘search and destroy’ was employed tocontrol mimosa outbreaks before they become amajor problem and prevent spread of the weedto other areas.It quickly became clear that it was not feasible tototally eradicate weeds within the park. In 1996,a Weed Management Strategy 19 for the park wasinstigated with seven key principles:• prevention; including wash-down facilities,implementing hygiene standards, educatingstaff, develop a local nursery for revegetation,educating residents and general public, liaisingwith adjacent landholders;• identifying ecosystems prone to invasion;• surveillance and early intervention;• minimising an area’s susceptibility to invasion;including feral animal control, rehabilitationof degraded areas and appointment ofRehabilitation Officer;• managing existing weeds;• researching existing and potential weedproblems; and• undertaking regular reviews.An area of about 20,000km 2 is difficult tomonitor, but Senior Park Ranger Buck Salausays that a zero tolerance policy combined withconstant monitoring and vigilance is the key tocontrolling Mimosa pigra. A team of four fulltimeweed officers regularly check floodplainareas for mimosa in four wheel drives and quadbikes during the dry season, or air boats duringthe wet season. Early eradication is critical, so themonitoring program runs year-round.Mimosa pigra was first detected in Kakadu atthe popular Yellow Waters Billabong in 1981and later that year at Munmarlary. Despite earlyeradication and monitoring of the Yellow Watersite, two years later a large infestation was foundnearby. Its spread to other areas is thought tohave been caused by humans and their vehicles.Large numbers of feral buffalo in the park werealso a major cause of spread and degradationof wetland areas until the buffalo eradicationprogram of 1985-89 dramatically reducednumbers.Seeds are placed in a bin ready for burning42 MIMOSA BEST PRACTICE MANAGEMENT MANUAL

Small plants are hand pulled or grubbed out.Larger plants are sprayed with herbicide usingspray units. If a plant has seeded, all seedsare carefully collected and then burned on sitewith a very hot fire to destroy them. Graslan®(tebuthiuron) is used to provide protection duringthe early wet season when access by both landand water is impossible. Aerial surveys are alsocarried out regularly. Buck estimates that about$600,000 is spent each year on staff, vehicles,helicopters, airboats and herbicides.Despite the cost, controlling small outbreaksis much cheaper than trying to control largeinfestations. Because of a history of controllingmimosa, rangers are able to focus on search andcontrol of small mimosa outbreaks, at an averagecost of $2/ha (1996). In comparison, control ofa large infestation on the Oenpelli floodplain inArnhem Land cost $200/ha each year over a fiveyearperiod (1991-1996) and control efforts arestill continuing today 20 .Buck says the continued support of traditionalowners has been critical to the success of theprogram. “The traditional owners are very awareof the threat it poses to the wetlands, to hunting.If they find a plant, they will report it to us.” Herecounts how the Gagadju Association instigatedthe idea for a mimosa program when the weedwas first detected in the park. The support ofland managers has meant a large amount ofresources have been committed to allow yearroundsurveillance of the park and ensure mimosadoes not get out of control.“We have a zero tolerance policy. Even just oneplant can cause big problems a short time later.Sometimes you find plants in the strangest ofplaces. If it is wet, it can grow there.”Constant monitoring is needed since the seedscan remain viable in some soils for up to 23years. Buck describes how the mimosa teamsreturn to mimosa sites to kill any seedlings whichmay have germinated. “We mark plots wherewe find mimosa with a picket, GPS the locationand keep coming back. Sometimes we findnothing, but you can find plants, years and yearslater. It is an ongoing program.”Buck explains that Kakadu National Parkeducates tour guides, junior rangers and seasonalrangers about mimosa so they can pass ontheir knowledge to members of the public andraise awareness of the weed. The mimosamanagement team also get together with peoplefrom Aboriginal communities such as Oenpelli toshare knowledge and experience.Buck says they have been lucky in havingthe support of management to employ fourdedicated staff on the job, 12 months of theyear and this has been the key to the program’ssuccess. Despite the large amount of resourcesrequired, the costs of allowing mimosa to spreadunchecked are many times greater. He seesmimosa management as a problem that will notgo away, but with constant vigilance and control,it can at least be restricted to small outbreaksand the prolific wildlife of Kakadu’s wetlands willnot be threatened by this tenacious weed.4. CASE STUDIESKakadu National Park Rangers get wet to remove a mimosa plant on the floodplains43

4.2 Case Study 2Malak Malak Land Trust, NTFor Malak Malak people,their country has a spiritual significancewhich ties them to its past and future. It isalso a place for hunting and gathering bushtucker including wallabies, goanna, fish andturtles. The invasion of Mimosa pigra at theDaly River floodplains threatens the habitatof wetland species and prevents access toimportant hunting and fishing areas.Malak Malak Land Trust lies in the Daly RiverRegion, 220km south of Darwin, just west ofLitchfield National Park.Albert Myoung is Senior Ranger and elder of theMalak Malak. He has been managing mimosaon country since he discovered a small infestationin the mid1990s which quickly grew into a largethicket.Albert’s mimosa story began when a visitingWeeds Officer, came to Malak Malak country tofind out whether mimosa had infested the region.“The officer showed me a picture, and he said,‘have you seen this?’ and I recognised it from thephoto, I said ‘yeah I’ve seen some, never seen thembefore.’” Albert describes how Weeds Officersshowed him how to cut and paste mimosa as wellas to use a knapsack and hand gun to spray. Albertinitially tried controlling mimosa by concentratingon the largest infestation at Parngala, an importanthunting ground, but it was hard work doing it allby hand. The weed continued to spread to otherareas, making it practically impossible to controleffectively from the ground with only a small teamof rangers.Albert noticed the drastic impact mimosa had onthe land within just a few years. “Parngala usedto be good hunting for wallaby, turtle, goannaand magpie goose. Mimosa is a no-good weedfor this country.” He describes how pest control isimportant in controlling mimosa.“Buffalo, horses and pigs – they make it worse!We’d like to get rid of the buffalo, but it’s toomuch for us, too dangerous. Pigs are alright – weeat pigs for tucker.”Malak Malak is surrounded by the pastoralproperties of Tipperary, Elizabeth Downs andLitchfield Station. It also includes some freeholdblocks of land used for mango crops or small-scaletourism operations which cater for visitors whocome to the Daly River to fish. Avid recreationalfishers travel across the country every April to takepart in the annual Barra Nationals.Albert by the banks of the Daly River44 MIMOSA BEST PRACTICE MANAGEMENT MANUAL

These days Rob Lindsay coordinates the MalakMalak ranger group; responsible for managingthe land trust against weeds, pests and fire.He says the variety of land uses in the regionmeans good cooperation is needed to controlmimosa effectively and prevent it from spreading.However, different priorities of landholders makecoordination a real challenge. “You can see areaswhere mimosa is not being controlled and it hasspread on to Malak Malak land.”Albert describes how they are keeping cattle outof mimosa-infested areas to prevent spread. Robsays the fence provides a good buffer zone toprevent spread and also allow access for groundcontrol. “Once you’ve got a boundary you canwork along the boundary and move in to shrinkthe infestation.”In 1998, Malak Malak signed the Mimosa Servicesand Funding Agreement (MSFA) with the IndigenousLand Corporation, Northern Land Council, TiwiLand Council and Northern Territory Government.The agreement has allowed the rangers to accessfunding for resources such as herbicides and hireof a helicopter for aerial spraying and surveying.The NT Weed Management Branch have providedadvice and assistance to Albert, resulting in a WeedManagement Plan which prioritises managementareas and has been successful in making weedcontrol methods more effective through integratedmanagement and timing. The Branch also providedtraining in mimosa ground control methods forMalak Malak rangers.Albert stands before the tank and storage arearecently constructed to facilitate more efficient aerialsprayingThe MSFA funds were put towards aerialspraying large infestations which could not becontrolled from the ground. The dead mimosawas then bulldozed to enable access for repeataerial spraying and ground control of seedlings.Ground control takes place in the dry seasonsince access is restricted in the wet season whenmuch of the wetland areas are inundated for 3-6months. Most recently, the group installed an11,000 litre water tank and storage area on siteto load a helicopter in the early wet season foraerial control operations.4. CASE STUDIESAlbert and Rob discuss their weed management plan with local weeds officer Michael Schmid45

Impressively, Albert and his team of rangerscleared a helicopter landing site by hand toallow access to the site when surrounding areasare flooded. He says the site will be very usefulwhen the Parngala area is aerial sprayed inDecember after seedlings emerge with the firstrains. “Now if it gets too wet here it’s all readyto go, they can come in with the chopper”.Regional Weeds Officer, Michael Schmid, saysthey plan to follow up this treatment in Aprilwhen floodwaters recede and seedlings areexposed once more. The water tank also meansthat access to water will be provided year-round,particularly during the dry season when therangers come out to do ground control.Perhaps the biggest challenge for Albert isattracting young Malak Malak out to country towork. “They come here and stay a few weeks,but then they go back to Darwin!” The rangersstay with Albert and his family, as there is a lackof accommodation at their small outstation ofMaddaingya. “We need to be able to provide ahouse, then we could get someone to stay, butwe don’t have the money.”Malak Malak Ranger Coordinator Rob Lindsaysays persistence is the key to managing mimosa.“It’s such a big area, it really is a long-term thing.We focus on one area, get on top of that thenmove on to another area.”He says managing the top of each catchmentto prevent downstream spread of seeds is vital.“We go up a creek until we find the last plant– that ‘s where you need to start, at the top ofthe creek.”Rob says they’ve found chemical control workswell in conjunction with other methods. Toincrease efficiency of ground spraying, they planto upgrade their current spray kit. “There is a bigspray unit which can hold about 400 litres whichcan be towed behind a quad bike. Otherwise wehave to go back to refill every 70 litres.”Albert and Rob say that at first theyunderestimated the amount of damage mimosacould do to the landscape. “It only took a fewyears to spread, we didn’t know it was so bad,that it had the potential to wreck country. Itreally is a shock to see how quickly it comes uponce it rains. You need to come back all thetime.”Albert stands next to the mimosa infestation at Parngala in 1998 and at the same place, ten years later46 MIMOSA BEST PRACTICE MANAGEMENT MANUAL

Back at Maddaingya, the Malak Malak womenare rearing and releasing macaria (Macariapallidata), a biological control agent whicheats mimosa leaves, as part of a trial with theWeed Management Branch Biological ControlSection. Albert’s sister Rita Purack describeshow they rear the moth larvae in cages to keepthem away from ants, and take them out to thetrial site when they become large pupae. Oncereleased, the pupae become moths a few dayslater and go on to lay eggs on another mimosaplant. “At first we didn’t know how to do itproperly, but then Natasha taught us properlyhow to do it and now we do it ourselves.”The Biocontrol group is redistributing macariain the Daly, Docherty and Moyle catchments toenhance biological control in these areas.Raising macariaWeed Sciences Technical Officer NatashaBurrows says so far the project at MalakMalak is going very well. “We have hadsome excellent results with six colonies rearedso far and they have also seen larvae at therelease site. At the moment the Malak Malakwomen are releasing agents on their own land.Hopefully if they keep going we can collectagents reared by them and redistribute it toother lands in the region.”Although the project has not yet been goinglong enough for it to have had an effect onthe infestation, the moth is known to beeffective in reducing the mimosa’s competitiveadvantage. “Elsewhere we have seen mimosastands totally defoliated. Macaria doesn’t killthe plant but it does stop it from producingseed and makes it more vulnerable to theeffects of fire and mechanical control.”Natasha says that since macaria defoliatesthe plant, foliar sprays will not be effective.Instead, infestations affected by macaria canbe burned or cleared by chaining.4. CASE STUDIESMacaria larvaeMature macariaMimosa plant eaten by macaria larvae47

4.3 Case Study 3Peter Faust Dam, QLDPeter Faust Dam,near Proserpine, in Queensland, is the onlyknown infestation of Mimosa pigra outsidethe Northern Territory.The dam is located on private land at the headwatersof the Proserpine catchment. It is used as apopular recreation area for boating and fishing, aswell as water storage for irrigation and domestic use.Mimosa pigra was originally detected at the Damby the landholder in February 2001. The infestationwas mapped from the ground using a GPS, boats,four-wheel drive vehicles and 13 staff members over10 days 21 . About 1000 plants were found at thehigh water mark. Seeds were physically removedfrom the plant by hand, then the entire plantwas uprooted and taken to a bunded area wherethe plants and seeds were burned. Another twoinfestations were found five metres under water.A subsequent aerial survey of the catchment viahelicopter did not find any other infestations.A follow up ground survey took place inSeptember 2001, detecting 150 seedlings inthe same area. The Peter Faust Dam MimosaManagement Group was founded to bringtogether stakeholders and develop a five-yearmanagement plan for the dam 21 .If this infestation had not been quickly controlled,mimosa would have cost the community, theenvironment and the Queensland economy. Itposes a great threat to the productivity of canefarming and cattle grazing, both major industriesin the region. Popular recreation and tourismactivities such as water-skiing, fishing and campingwould also be compromised if mimosa wasallowed to spread throughout the region.In April 2002, mimosa seedlings were foundextensively throughout the area, many withinMelaleuca spp. stands. Some areas were found tohave up to 400 mimosa plants per 25m 2 .A 17km access road was bulldozed to spraythe mimosa infestations with melfuron-methyl.Areas of melaleuca stands containing mimosawere also cleared so the seedlings could bedetected and controlled. Wash-down sites andhygiene guidelines were established to preventfurther spread by vehicle and cattle movement.The Management Group decided to undertakemonthly inspections of the area and three annualsurveys of the entire dam perimeter 21 .A state-wide education program was launched toraise awareness of the risks of spreading mimosa.Local landholders were trained in identifying andcontrolling mimosa. A land management programincluding feral pig control and fire managementwas also established to prevent further spread.Principal Land Protection Officer, Steve Matheson,said the location of the infestation at theheadwaters of the Proserpine River meant therewas a high risk of spread. Without proper control,the mimosa infestation poses a threat to theagriculture, recreational fishing and tourism sectorsas well as waterbird habitat.Peter Faust Dam48 MIMOSA BEST PRACTICE MANAGEMENT MANUAL

“We did consider closing the dam to fishing – thatwould have had a big impact on recreationalfishers, so they use both wash-down facilities.”Steve says that support from local and Stategovernments has been crucial to the success ofthe program, which now costs about $200,000a year. “State and local ownership have madesure this project has worked, there is great cooperationbetween the Whitsunday RegionalCouncil and the Queensland Government.”Signs alert visitors to the Mimosa pigra infestationat the Dam“It had the opportunity to spread throughout thecatchment and down the Proserpine River. Thereare a lot of wetlands in the area and it’s the rightclimate for it to spread.”In September 2002 a survey of the entire damperimeter found seedlings but only two matureplants. The most recent survey in 2008 foundjust four plants. No mature plants have beendetected since 2004. Two people are currentlyemployed full-time to survey and control thearea. Plants are pulled out by hand wherepossible, or foliar sprayed. “Every plant they seeis pulled out and destroyed. The dam is used foragricultural irrigation and drinking water – weneed to be very careful with what we can use.”The Peter Faust Dam is an important site forrecreational fishing and tourism. Steve saysfishers have recognised what they have to lose ifmimosa is allowed to get out of control and havebeen very supportive of hygiene practices such asthe wash-down.He has found constant vigilance and monitoringis the key to controlling mimosa. “You can’t turnyour back on it for a couple of months – if you do,you end up with seeding plants there straight away– you need to do diligent surveys, be preparedto wade out into waist deep water.” But findingpeople to do the job has been a problem. “Wehave trouble attracting and retaining staff as it is avery hands-on, very hot and tedious job – retentionof staff is our biggest issue.”Steve says that it is critical landholders andmanagers can readily identify and report mimosainfestations immediately. “Be aware of this pestand please, don’t try to hide it from us – makesure you tell us straight away. Always keep an eyearound the edge of water bodies on your property,particularly if it is used by recreational fishers.”He says that at Peter Faust Dam, although theywill be monitoring for mimosa for many yearsto come, he is pleased with the success of theprogram. He encourages Northern Territorylandholders with mimosa on their property tomake sure they control it properly. “Don’t let itget away – get rid of it, be diligent and stop anyopportunity for it to spread.”4. CASE STUDIESThe washdown station at Peter Faust Dam is well utilised by visitors49

4.4 Case Study 4Twin Hill Station, NTIn the early 1980s, mimosathreatened to take over Twin Hill Station’swetlands – blocking access to billabongs andtaking over important native habitat.Twin Hill Station is a pastoral property locatedon Wagait Aboriginal Land in the Finniss Rivercatchment. The station shares its boundary withthe Aboriginal clans of Werat and Wadjigan aswell as Litchfield National Park, a popular day trip100km south-west of Darwin.Mimosa threatened to take over the area’swetlands in the early 1980s – blocking accessto billabongs and taking over important nativehabitat. An integrated management programhas allowed the land managers to gain controlover mimosa on the property, with the assistanceand support of local agencies.Twin Hill Station manager Colin Deveraux clearlyremembers when Mimosa pigra started becominga problem for the area in the early 1980s. “Wecouldn’t get to our favourite fishing spots becausemimosa prevented access to the bank.It started taking over roads, blocking access.Then we noticed when we went hunting, feralbuffalo and pigs were hiding in these infestations– it was getting worse!”Colin and his family started experimentingwith control methods, trying to find a way toeradicate the mimosa thickets which threatenedthe biodiversity, cultural values and productivevalues of the property. “We tried all sorts ofthings – I remember buying a flamethrower! Atfirst it would work, but it would come back thenext year twice as thick. Then we started tolearn from the government about the differentchemicals you could use. We adopted some oftheir methods and started achieving results acouple of years later.”Twin Hill is home to several threatened species,including the rare grass owl. Colin explains thearea is so rich in wildlife it is listed as a Wetlandof National Importance. “Mimosa displacesplants and habitat for all native animals of thefloodplains, including turtles, fish, crocodilesand birds.” The area is also Aboriginal land ofsignificance to the white eagle (Rak Mak MakMarrananggu) people. “Mimosa can swallow upwhole billabongs – it makes it very hard to passon cultural knowledge when this ‘curtain’ hasbeen placed over everything.”The floodplains are an abundant source oftraditional foods such as the long-necked turtleand magpie goose. “Mimosa replaced magpiegeese nesting areas, causing the population todecline until we reclaimed the floodplain.A severe mimosa infestation at Twin Hill Station50 MIMOSA BEST PRACTICE MANAGEMENT MANUAL

We allow these areas make their comeback – welet nature take its course as the native grass seedswash down and regenerate naturally. The nativegrasses came back and now you wouldn’t knowthere was mimosa ever there. That is our secret.We use grass like a blanket to cover the soil, butif a pig digs it up the mimosa seeds will germinatestraight away.” Feral pigs are managed throughshooting. “Recently my son Calvin shot 300 pigsin six weeks!”Magpie gooseNow we’ve got the highest goose population we’veseen since we’ve had mimosa. The short and longneckedturtles dropped off but now they’re makinga comeback.” Colin adds that since gaining controlover mimosa, the saltwater crocodile nestinghabitat has increased to the point where they needto harvest eggs to keep the crocodile populationfrom getting out of control.Cattle production at Twin Hill Station is themajor enterprise for the White Eagle AboriginalCorporation. Mimosa threatens cattle productionby shading out cattle feed, blocking access andtaking over productive land. Colin explainshow the station’s stocking rates have improveddramatically since large amounts of mimosa havebeen removed and paddocks have been allowedto revegetate. “Hospital paddocks, we call them.The Corporation prioritise areas for control andmonitoring by identifying habitats vulnerableto invasion, identifying vectors of spread,analysing hydrological patterns to identify highriskareas, limiting soil disturbance in wetlandareas and establishing buffer zones around largeinfestations 22 .Fire management is also an important part ofmimosa control at Twin Hill. Colin has found thatmimosa increases the intensity of fires, killingany nearby Melaleuca trees. “Fires around herego down into the deep cracks of the black clayfloodplain soils, so they can emerge in anotherlocation by travelling under ground. Grazing helpsprevent fires by reducing the fuel load. We like tosay we live off the top half of our grass.”Colin says that after 14 years of controllingmimosa on the property, they are now at the stagewhere they can hand pull any seedlings detected,using basal bark methods if the plant is too big.4. CASE STUDIESFeral pigs disturb wetlands, making them more vulnerable to weeds such as mimosa51

“You have to come back every year – you need amap of the area and you’ve got to keep records ofwhere you went, when and what you did.”“The Northern Territory Government work withus – they have supplied us with equipment andadvice. We also participated in a control trialwhich attempted to identify how different controlmethods – chemical, fire or mechanical – couldbe married up with biocontrol. They foundthat using a suite of control options gave thebest result – depending on the nature of yourfloodplain. ‘Integrated Control’ was the namethey gave it.“The researchers noticed that after fire you getmassive regeneration of seed when it is stimulatedwith fire, which can easily then be aerial sprayed.They also found biocontrol agents were moreeffective on seedlings than mature plants.We’ve received most of the biocontrol agentsthey released. I’ve noticed that biocontrol hasslowed down growth of mimosa – it is not as tall,vigorous or dense and has longer growth periods.It’s not a short-term solution, but it might work inthe future.”Colin says that although they have successfullyremoved the large mimosa infestations, theyneed to monitor sites every year as there is stillseedlings coming through. “You need to get inwith the aerial spraying when you’ve just got a bitof rain to get things going, before the wet seasonfloods, around mid-November.It’s a lot of money to outlay and you’ve only got asmall window of opportunity when it is susceptibleto the herbicide.”Apart from aerial spraying, a large component ofthe Twin Hills control program is foliar sprayingfrom the ground. The opportunity to do this islimited by access. “Once the rains come, you can’tget out on to floodplains again until July/August.Even quad bikes can’t cope with this country – wehave specialised vehicles so they don’t bog easily.”Large areas are aerial sprayed from an aeroplane,which is followed up by helicopter. Colin says theydon’t use mechanical clearing or fire to remove thedead mimosa material as they’ve found it breaksdown after about three years.Colin estimates it costs them about $150,000 ayear to control approximately 10,000 hectares ofland, which he considers a worthwhile investment.“If we hadn’t had a weeds program, mimosa wasin the process of colonising everything!”“The hardest part is to begin a program – youneed to realise the area you target this year needsto be budgeted for the next five years. It’s nogood targeting it all in one lump because thereis a seedbank in the soil which doesn’t diminishfor at least five years! In some areas we’ve foundmimosa has come back 20 years later.”He finds the biggest problem is encouragingneighbouring landholders to do the same. “Youcan fly up to the boundary and there is a wallof mimosa as they are not managing it on theirproperty.” Now, thanks to a NT Cattlemen’sAssociation grant, they have created a 100mbuffer zone at the boundary to prevent mimosaseeds spreading into Twin Hill. “Now the grasshas grown up so the mimosa seeds hit the grassand get stuck, but floodwaters can still take theseeds kilometres away as they float.” Colin isassisting his neighbours by training some of theland managers in mimosa control so they canlearn from their experience at Twin Hill.An infestation at Twin Hills before and aftertreatment with herbicideThe same area is now clear of mimosa, allowingaccess to the billabong52 MIMOSA BEST PRACTICE MANAGEMENT MANUAL

4.5 Case Study 5Adelaide River, NTMimosa was first recognisedas a serious problem when a largeinfestation was found at the AdelaideRiver in the 1950s and it continues to becontrolled today.The Adelaide River catchment is a mosaic ofdifferent land-types, including Aboriginal land,pastoral properties, freehold land and vacantcrown land. The area is used for a variety ofactivities including tourism, grazing, huntingand fishing. This presents a complex challengefor prevention of spread and control of mimosa,requiring good cooperation between agenciesand land holders.Vacant Crown Land (VCL) is land owned by theCommonwealth and managed by the NorthernTerritory Government under the Crown LandsAct. The land is managed by governmentagencies to ensure it does not assist the spreadof weeds and pests. Adelaide River VCL ismanaged by the Department of Planningand Infrastructure with assistance from theDepartment of Natural Resources, Environment,The Arts and Sport Weed Management Branch(Weeds Branch).Map of land tenure in Adelaide River regionshowing VCL (in pink)The land includes large sections of the AdelaideRiver adjacent to land managed by CoomalieCouncil at Adelaide River township. Pocketsof VCL throughout the catchment also shareboundaries with freehold landholders, DjukbinjNational Park and pastoral landholders.Mimosa infestations occur all along the riverand surrounding areas, from upstream ofthe Adelaide River township through to thefloodplains beyond the Arnhem Highway.Mimosa outcompetes native vegetation, formingdense monocultures in the watercourses andfloodplain of the Adelaide River. Infestationsthreaten the viability of activities on the river,such as fishing and wildlife cruises, as well asreducing habitat available to native flora andfauna.4. CASE STUDIESA local landholder checks out a mimosa infestation at Little Finniss River (J.Page)53

Regional Weeds Officer, Michael Schmid,describes how the diversity of land-uses andland managers in the region mean a coordinatedapproach is needed to manage mimosaeffectively.The Weeds Branch, Department of Planning andInfrastructure, Greening Australia and CoomalieCouncil are working with landholders andIndigenous groups to develop a catchment wideapproach and avoid reinfestation by seeds carrieddownstream.Recreational fishers and hunters are encouragedto thoroughly inspect their boats and vehicles forseeds before leaving the area to avoid spreadingseed. The Weeds Branch also work with nearbypastoralists to ensure they control mimosaon their land effectively by concentrating onupstream infestations, managing stocking ratesnear infestations and maintaining good grasscover.Michael says every landholder must controltheir patch for weeds. “Significant reductionsin mimosa have been achieved however this isdependent on a coordinated effort with everylandholder properly managing the weed on theirproperty.”Biodiversity Conservation Officer of GreeningAustralia NT Jaemie Page describes how both theAdelaide and Finniss Rivers originate from smallsprings and creeks in the escarpment countryaround the Coomalie Council region. “The areacomprises hundreds of freehold blocks managedby many landowners with different capacity andmotivation to manage mimosa on their land. Inmany cases blocks are vacant so no managementis occurring.”Access to mimosa-infested tributaries in thearea is often difficult. Mimosa plants growintertwined with bamboo and other riparianplants, making them difficult to locate andcontrol.Jaemie reports how many land managers in theregion have found foliar spraying with glyphosateas effective as broad leaf sprays and much saferto use for landowners with less experience inusing herbicides. “Basal bark and cut-stumpwith broad leaf herbicide and diesel are bothused, but cut-stumping is preferred as it uses lessdiesel than basal bark, reducing transport costsand the risk of pollution.”Back at the Weeds Branch, Michael Schmidexplains how they designed a VCL Adelaide RiverWeed Management Plan. “We conducted aerialsurveys to map the distribution of mimosa.Ngatpuk rangers brave the croc infested waters of the upper Adelaide River to access mimosa (J.Page)54 MIMOSA BEST PRACTICE MANAGEMENT MANUAL

We then allocated management areas accordingto the size, density and location of eachinfestation and worked out what areas could betackled first given the available budget.” Controlmethods for each management area weredetermined by the nature of each managementarea. “For example, if it’s a large infestation, wewould be looking to do aerial spraying in theearly wet season, then send out a contractor todo follow-up ground control before the plantsseed and as new seedlings germinate in the earlydry season.”Michael adds that follow up control is crucial tobreak the seed cycle. “The VCL program on theAdelaide River has been very successful becauseit has been coordinated and well timed. Timing iseverything when it comes to controlling mimosa.”Local contractor Geoff Baker describes howhis team goes in on the ground to foliar sprayseedlings once the Weeds Branch have carried outaerial spraying and cleared the dead mimosa. “Weuse Brushoff® which is relatively economical butwe’ve found Starane® is much more effective.We also use Graslan® for isolated infestationsearly in the wet season and record waypoints oflarger infestations to target for aerial spraying.We have found soil-applied herbicide to be veryeffective and quicker than foliar spray and can beused when plants are not actively growing.”Geoff says he has noticed wildlife returning tothe area after mimosa control. “The billabongshave come back to life where we have beenconcentrating control efforts near MarrakaiCrossing. Three years ago the water wasstagnant and slimy – now that the mimosahas gone, the billabongs are full of water lilies,ducks, waterbirds and fish.”4. CASE STUDIESThis billabong at Marrakai Crossing has come back to life just 12 months after the mimosa infestation chokingits banks was treated55

New technology may help clear up wetlandsA problem for managers is removing the deadmimosa material following herbicide treatment,to make way for follow up control. “Access toseedlings is difficult with the dead stick there– we need to get rid of it so the contractorscan get in for ground control.”The standard method is to use bulldozers toeither chain and windrow or pile up the deadmimosa and burn it. Now a unique machinewhich mulches dead mimosa on site is currentlybeing trialled by the Weeds Branch in theAdelaide River region to find out how it weighsup against other methods of mechanicalcontrol.Regional Weeds Officer Michael Schmidsays, depending on how much it costs, thenew technology looks promising. “The mainadvantage is that we don’t have to burn, whichreduces carbon emissions, returns the organicmatter to the soil and means the area is lessvulnerable to erosion. Other advantages arethat the mulcher is easy to clean and allowsyou to leave native trees standing. However,further investigation is required to determinehow the costs compare to other methods. If itis very expensive, mulching may not be viable,particularly for large areas.”Mulching allows access to treat seedlings withherbicideThis mulching machine may be the answer to removing dead mimosa with minimal impact56 MIMOSA BEST PRACTICE MANAGEMENT MANUAL