Adapted over thousands of years to withstand high temperatures and droughts, the plants of northern Victoria and the southern Riverina provide habitat for native birds and insects. Local plants are usually resistant to local insect pests and may therefore be easier to grow. Furthermore, local plants cannot become garden escapes, environmental weeds, which may be costly to remove from riversides and bushland.
Unfortunately, thousands of plants have been introduced into our region from other parts of Australia and from overseas, both deliberately and accidentally. Some of the introduced plants are important agricultural plants providing food, oils and raw materials. Useful plants which are not a problem in bushland or gardens are not weeds. Weeds are plants which grow where they are not wanted. Therefore, a plant introduced from another part of Australia can be a weed in this area.
“From the Mimosa pigra threatening Kakadu to pasture grasses threatening fragile desert ecosystems and blackberries choking southern streams and alpine meadows, non-native species are running rampant after a century of unchecked growth. It’s a silent invasion that is redrawing the Australian landscape.”
~ Brad Collins, The Bulletin, 5th August 1997
In June 2005, the Australian Government announced a $40 million programme to attack weeds and asked State and Territory governments to ban the sale in nurseries of 20 listed weeds of national importance (including Lantana, Prickly Acacia, Rubber Vine, Bridal Creeper, Bitou Bush and Salvinia). The importation of about 3,300 potential weeds has been banned.
At the moment, plants which are regarded as noxious weeds in one State are sometimes still being sold in nurseries in other States. Despite spreading like wildfire throughout part of the Northern Territory, Gamba Grass, for example, is still being sold and planted in Queensland.
Over 30,000 plant species have been introduced into Australia. Of these, about 3,000 have become feral (weeds). About 65% of weeds are ‘garden escapes’. A further 7% of weeds were introduced to ‘help agriculture’. There are also a number of native weeds, e.g. a Western Australian plant, Sollya heterophylla (Bluebell Creeper), has become a pest in south-eastern Australia.
Many roadsides and fields are covered by the purple flowers of Patersons Curse each spring. But there are many other, even worse, weeds. In fact, Australia has about 3,000 foreign weeds and a number of native weeds. About 10 new weeds are detected each year, many of them garden escapes.
Every piece of bushland, every farm, every pasture and every garden is subject to invasion by weeds. Tropical areas are sometimes hard hit. But weeds are found even arid and remote areas.
A CRC for Australian Weed Management was established some years ago. A provider of information, it has produced a number of publications, including a weed manual for farmers which sets out ways in which farmers can help combat problem weeds. All CRCs are now required to meet commercialisation criteria. Because the Weeds CRC is not able to meet the criteria, the Australian government will shortly cease funding it. The Centre claims it saves land managers at least $23 for every $1 it receives. The CRC was subject of a Landline story (ABC-TV) on 20th May 2007.
Most of the 340 weeds causing environmental harm in NSW were deliberately introduced as garden and pasture plants. Few are banned, and many are still being sold. There are also no restrictions on the sale of thousands of potential new weed species. More than 99% of the 30,000 exotic plant species in Australia can be planted freely in NSW. Their impact is greater than many may think, in many more ways than you may have thought possible, and the ramifications for birds and other wildlife are many and varied.
In August 2010, a telling report on the state of weeds in NSW, called Stopping NSW’s Creeping Peril was launched. The report discusses many of the issues that surround weeds and their control and management. The report calls for better weed laws, policies and funding in NSW to tackle weed invasions that are overwhelming authorities and landholders.
Booklets, most of them with coloured photographs, are available from local catchment management authorities, DPI offices and/or shire councils. One of the best such booklets is Weeds of the Goulburn Broken: A field guide to terrestrial and aquatic weeds, available from Goulburn-Broken CMA and local Victorian Department of Primary Industries offices. A similar publication, Weeds of the North Central Region, is available from the North Central CMA. The booklets are more useful than this web page because the publications have coloured photographs of all the weeds they describe. At the moment, weeds may be classified in different categories in different CMAs. This problem may be alleviated with the impending merger of the North Central and Goulburn Broken CMAs.
Control Techniques. Consult with the Department of Primary industry and/or your CMA for advice regarding control techniques.
Ten of the worst environmental weeds in our district
1 Paterson’s Curse (Echium plantagineum) (W3, RC)
Introduced as a garden plant by the Paterson family, Paterson’s Curse is common along local roadsides, on disturbed soils and on sandy loam. It can be spread by machinery. The weed has magneta-coloured flowers. The nectar is claimed by some to be carcinogenic. It is particularly bad in Terrick Terrick National Park.
2 Arrowhead (Sagittaria graminea)
Arrowhead is a water weed that’s fast spreading along channels, constricting water flow. An outbreak has occurred in the Barmah-Millewa wetlands. Arrowhead spells bad news for irrigators. Control is difficult as the NSW EPA is reluctant to allow the use of chemical sprays in waterways.
3 African Boxthorn (Lycium ferosissimum) (RC, W2)
This prickly shrub to five metres in height can form impenetrable thickets and is very difficult to eradicate. Readily resprouts if cut or burned. Its spikes cause injury and can puncture car tyres. It often harbours such pests as rabbits and foxes.
4 Cape Weed (Arctotheca calendula)
Cape Weed is an invasive weed from South Africa. It is widespread, infesting vast areas.It prefers soils high in nitrates such as those of sheep yards. It has yellow flowers with many petals and a dark centre.
5 Canary Island Palm (Phoenix canariensis)
Introduced as a garden ornamental, these palm trees are spreading into local bushland where they are very difficult to eradicate. Even small palms defy a ‘Whipper Snipper’ and quickly develop a deep weed system so that control by hand weeding is not practical.
6 Peppercorn (Schinus molle)
Being hardy, this tree was once widely planted on farms. Over the years, it has escaped into bushland. It harbours mosquitoes and may drop duco-damaging gum on vehicles parked under it. Fortunately, most farmers are now landscaping with indigenous plants.
7 Gazania (Gazania linearis)
Despite the fact that these low growing plants with large flowers are spreading along roadsides and into bushland, Gazanias are, unfortunately, still sold and grown by some; invasive and hard to eradicate.
8 Bridal Creeper (Myrsiphyllum asparagoides)
Bridal Creeper likes sandy and friable soils. It has invaded some areas of natural bushland, e.g. sandhills in Victoria Park and along the lower Campaspe River, Echuca. Bridal Creeper smothers ground layer plants. Leaf Hoppers and a rust have been introduced in the hope they can help control it.
9 Parrot’s Feather (Myriophyllum aquaticum)
Parrot’s Feather is a bright green freshwater herb which closely resembles our native Milfoil. It has the appearance of a tiny feathery conifer. It spreads from stem fragments, is invasive and difficult (impossible?) to control. Out-competing Milfoil and other natives, it is rampant in the National Channel near Gunbower. Sterile plants appeared a few years ago at the headworks of Torrumbarry Weir and appear to have been spread by anglers and birds. In four years, this weed has spread from covering 4ha to over 120 hectares! It is likely to reach the Murray. It is in Campbells Creek and threatening the Loddon River. Despite being a weed of national significance, it can still be propagated and sold in Victoria because, despite being very similar to native Milfoil in appearance, it is a popular aquarium plant! A beetle eats the plant only to water level; biological control seems unlikely to be successful. Information to assist with the identification of Parrot’s Feather can be found at Goulburn-Murray Water’s web site.
10 Scotch Thistle (Onopordum spp) (W2)
A common weed alongside local waterways and irrigation channels. There are several other ‘thistles’ which are a nuisance locally.
The Victorian Department of Conservation of Natural Resources has published an excellent booklet called Environmental Weed Invasions in Victoria. It lists an alarming number of environmental weeds, and outlines the dangers they pose.
Environmental weeds in our district
Here is a list of some of the worst weeds and potential weeds in the southern Riverina and northern Victoria:
African Boxthorn (Lycium ferosissimum) (RC, W2), prickly shrub which can form impenetrable thickets and which is difficult to eradicate.
African Daisy (Winged Groundsel), (Senecio pterophorus)(RP)
African Feather Grass (Penniselum macrourum) (RP)
African (Weeping) Lovegrass (Eragrostis curvula) (RP)
Alligator Weed (Alternanthera philoxeroides) (N; P), a nasty aquatic weed which can clog waterways; has hollow stems and white, ball-shaped flowers.
Amsinckia; Yellow Burr Weed; Buckthorn (Amsinchia spp) (RC); an erect herb 70 70cm in height with yellow flowers.
Arrowhead (Sagittaria graminea), a particularly nasty aquatic weed which can clog lagoons, backwaters and channels
Artichoke Thistle (Cynara cardunculus) (RC)
Arum Lily; aza Funeral Flower; Death Lily (Zantedeschia aethiopica); large fleshy, green leaves and very large white sheath flowers with yellow inside
Basket Willow, undermines waterway banks, impedes water flow and outcompetes natives;
Bindi-eye (Bindii) (Tribulus terrestris) (RC) This weed has been particularly widespread over recent summers, finding its way into urban lawns as well as pastures; the three-cornered burrs can puncture the tyres of bicycles and even motor vehicles. The burrs can damage the feet of animals and are sometimes a major nuisance.
Blackberry (Rubus fruticosus) (W2; RC), invasive, prickly shrub.
Black Knapweed (Centaurea nigra) (N; P), prohibits germination of other species and not palatable to stock; has reddish-purple flowers.
Boneseed (Bitou Bush) (Chrysanthemoides monilifera) (P; RP)
Box Elder; Ash-leaf Maple (Acer negundo); deciduous tree with clustered, hanging leaves
Boxthorn (see above) (RC)
Briar Rose (Rosa rubiginosa
Bridal Creeper (Myrsiphyllum asparagoides), (see above) (RW)
Broomrape (Orbanche spp) (N)
Buffalo Burr (Solanum rostratum)( W3)
Cabomba (Cabomba caroliniana) (noxious W4g in NSW), a nasty aquatic weed which restricts water flow.
California Burr (Xanthium sp) (W2)
California Thistle (Cirsium arvense) (RC)
Caltrop (Tribulus terrestris) (RC) ~ See Bindi-i
Camel-thorn (Alhagi maurorum) (P)
Canary Island Palm (Phoenix canariensis) (Canary islands), difficult to eradicate, harbours rodents and starlings
Cape Broom (Genista monspessulana); an erect shrub to 3m (RC)
Cape Tulip (Moraea spp) (W2, RC)
Cape Weed (Arctotheca calendula) an invasive weed from South Africa
Carpet Grass (Axonopus affinis)raea spp) a creeping, shallow-rooted summer perennial grass that can form dense mats;
Castor Oil Plant (Ricinus communis); shrub to six metres with toxic seeds and toxins in the leaves; deadly.
Cherry Plum (Prunus cerasifera)
Chilean Needle Grass (Nassella neesiana) (N; RW); tussock grass to 1 metre in height which invades native grasslands and agricultural lands; difficult to eradicate.
Cockle Burr (Xanthium sp) (W2)
Columbus Grass (Sorghum x alumum) (W2)
Cootamundra Wattle (Acacia baileyana); commonly planted but seedlings quickly appear; not native to the greater Echuca region. Just because a plant is an Australian native does not mean that it cannot become a weed outside of its home range, in this case being the Cootamundra area.
Dense Water Weed (Egeria densa), a nasty aquatic weed which forms dense mats, restricting water flow; similar in appearance to Hydrilla, a native aquatic grass.
Desert Ash (Fraxinus angustifolia), an introduced tree.
Dock; a weed often found along roadsides and in pastures.
Dodder (Cuscate campestris) (W2, RC), parasitic on trees, box-ironbark forest infestations seem worse following logging; usually not a huge problem.
Egeria ~ see Dense Water Wee;
English Broom (Cytisus scoparius), (RC); a shrub which invades bushland even in alpine areas.
English Ivy (Hedera helix); can form dense mats and smother indigenous ground cover
Fennel (Foeniculum vulgare) (RW); an erect herb.
Gazania (Gazania linearis) still sold and grown by some; invasive and hard to eradicate
Golden Thistle (Scolymus hispanicus) (RC)
Gorse (Ulex europaeus) (N; RC), invasive shrub with yellow pea-like flowers introduced as a garden hedge
Great Mullein; Velvet Dock (Verbascum thapus) (RC); an erect herb to 2.5 metres in height
Hardheads (Acropitolon repens) (W3, RC)
Hawthorn (Crataegus monogyna) (RC); an erect shrub which harbours feral animals
Hoary Cress (Cardaria draba) (RC); an small erect herb
Horehound (Marrumbium vulgare) (W2, RC); herb with mint-like errated-edged leaves which invades pastures and reserves.
Horestail (Equisetum spp) (N; P); erect herb with asparagus-like leaves
Illyrian Thistle (RP)
Ivy-leaf Sida (Malvella leprosa) (P); herb to 30 cm in height with green ‘Shell’-like leaves
Johnson Grass (Sorghum halepense) (W2)
Karoo Thorn (Acacia karroo) (N)
Kochia (Kochia scoparia) (N)
Kylinga; Mullumbimby Couch (Cyperus brevifolius); shiny, green sedge to 40cm in height.
Lagarosiphon (Lagarosiphon major) (N, P), aggessive aquatic weed with stiff, dark green leaves arranged in alternate spirals along stems. The good news is that there are no known remaining infestations in the region.
Mesquite Bush (Prosopis spp) (N,P), six species of small tree/shrub, highly invasive.
Mexican Feather Grass (Nassell nussima) (syn. Stipa tenuissima) (N)
Miconia spp (N)
Morning Glory (Ipomoea indica); climber with purple flowers
Nodding Thistle (Carduuds nutans) (P)
Noongoora Burr (Xanthium strumarium) (W2, RC), an erect weed usually less than a metre in height (but can grow higher) with inconspicious flowers in clusters in late summer.
Olive (Olea europaea); evergreen tree often grown in cultivation; invades bushland areas.
Onion Weed (W3)
Pampas Grass (Cortaderia selloana); tussock grass with long, drooping leaves and white plume flowers.
Parrots Feather (Myriophyllum aquaticum), a nasty bright green aquatic herb which forms dense mats, similar in appearance to Milfoil; difficult to control and quickly becoming a major problem.
Parthenium Weed (Parthenium hysterophorus) (N,P), prolific seeder, causes dermatitis and asthma in some people.
Paterson’s Curse (Echium plantagineum) (W3, RC), can dominate roadsides and pasture, spread by seeds (e.g. in wheels of vehicles).
Peppercorn (Schinus molle), a tree which harbours mosquitoes and drops duco-damaging gum on vehicles parked under it;
Perrenail Ragweed (Ambrosia psilostachya) (P)
Phalaris (Phalaris aquatica); domineering erect grass to 150cm in height; deliberately introduced by a regional agricultural college as stock feed;it grows in clumps and poses a severe fire risk.
Poplar ~ see Silver Poplar;
Poverty Weed (Iva axillaris) (P), competes with cereal crops
Prairie Ground Cherry (Physalis viscosa) (W3, RC)
Ragwort (Senecio jacobaea) ~ toxic to stock;
Rhus Tree (Toxicodendron succedaneum) (W2)
Saint John’s Wart (Hypericum perforatum) (W2, RC)
Saffron Thistle (Carthamus lanatus)
Salvinia (Salvinia molesta) (N, P) ~ a free-floating aquatic fern which forms dense mats and reduces dissolved oxygen level, sterile but reproduces from fragments. It’s leaves are oval-shaped and covered in waxy hairs. Submerged leaves act like, and look like, roots. Spreads quickly. Seems to prefer small pondages.
Scotch Thistle (Onopordum spp) (W2)
Senegal Tea Plant (Gymnocoronis spilanthoides) (N) ~ forms a mass of floating vegetation impeding water flows (unfortunately not declared in Victoria)
Serrated Tussock (Nassella trichotoma) (RV)
Siam Weed (Chromolaena odorata) (N)
Silverleaf Nightshade (Solanum elaeagnifolium) (W3, RC)
Silver Poplar (Populus alba); tree to 12 metres
Sour Sob (Oxalis pescaprae); a perennial herb with bulb-producing, underground stem. The leaves are clover-like and the flowers are bright yellow trumpets. Very hard to control and poisonous to sheep in some cases. All too-common in many domestic gardens and disturbed areas.
Spiny Burr Grass (Cenchrus longispinus) (RC); erect grass with spike-like flower heads.
Spiny Rush (Juncus acutus) (RC)
Spotted Knapweed (Centaurea maculosa) (N)
Spear Thistle; (RP in Goulburn Broken CMA area)
Spiny Emex (Three-corner Jack) (Emex australis) (W3) ~ three-pronged burrs can inflict pain and puncture tyres.
Spiny Rush (Juncus acutus)
Sweet Briar Rose (Rosa rubiginosa) (RC); erect, thorny shrub to three metres in height; pink or white flowers
Sweet Pittosporum (Pittosporum undulatum) ~ native to eastern Australia, broader leaves than our indigenous Weeping Pittosporum which is not regarded as a weed.
Tangled Hypericum (Hypericum triquetrifolium) (P)
Thistle, Artichoke (Cynara cardunculus) (RP)
Thistle, Golden (Scolymus hispanicus) (RP)
Thistle, Nodding (Carduus nutans) (SP)
Thistle, Safron (Carthamus lanatus) (RC)
Thistle, Slender (Carduus tenuiflorus) (RW)
Thistle, Spear (Cirsium vulgare) (RW)
Thistle, St Barnaby’s (Centaurea solstitialis) (RC)
Thistle, Star (Centaurea calcitrapa) (RW)
Thistle, Stemless (Onopordum acaulon) (RW)
Thistle, Variegated (Silybum marianum) (RC)
Thorn Apples (Datura sp) (RC)
Tree of Heaven (Ailanthus altissima) (W2)
Tutsan (Hypericum androsaemum) (RC); erect shrub to 1.5 metres in height
Umbrella Sedge (Cyperus eragrostis) ~ perennial weed of roadside gutters and drains
Water Hyacinth (Eichhornia crassipes) (N,P) ~ a nasty free-floating aquatic weed which clogs waterways; easily identified by its swollen, bulbous leaves and purple flowers with a yellow-spot on the upper petal. One of the world’s worst weeds because of its ability to quickly clog waterways. Contact DPI to arrange for speedy, safe removal.
Water Lettuce (N)
Wheel Cactus (Opuntia robusia) (RC) ~ fleshy stems with nasty spines; a type of Prickly Pear sometimes found along the Campaspe River and in Box Forests (e.g. Kamarooka Forest and Wychitella NCR). It is out of control in some places, e.g. Mt Buckrabanyule where locals have frequent work bees to inject individual plants with a weed killer.
Wild Garlic (Allium vineale) (RP)
Willows (Salix spp) (noxious weeds W4g in NSW; RW) ~ the sale of most species is banned in NSW and Victoria.
Yellow Water-lily (Nymphaea mexicana) ~ has attractive flowers but can block waterways and make wetlands unsuitable for water birds.
More about weeds
Farmers would, no doubt, add lots more weeds to the list on this site. And there are other plants which, if introduced, could become problem weeds.
A potential pest if introduced is Pride of Bolivia (Tipuana tipu), a tree with aggressive roots which spreads prolifically. Fortunately, it may still be absent from our district.
What you need to do. For details on actions required of land holders who have weeds on their property, see NSW Agriculture’s Noxious Weed Site and Victoria’s North Central CMA (03 5448 7124).
The Shire of Murray has trained 15 of its staff in the safe use of appropriate herbicides, and staff will use this knowledge to control and eliminate weeds from parks, gardens, lanes, drains, road shoulders, under signs, etc. In the Shire. The consideration of appropriate products has resulted in a preference for conservative, slower-acting and safer chemicals with a Nil Dangerous Goods Classification or the lowest Poison Schedule being selected. The Central Murray Country Council is in charge of noxious weed control in Murray Shire and intends to inspect properties within the Shire for noxious weeds.
Most weeds were deliberately introduced into this country. Of Australia’s 18 worst environmental weeds, all but two were deliberately introduced as pasture/fodder grasses or as ornamentals. Some weeds are garden escapes. Even more were introduced as pasture grasses.
At least 60 of Australia’s weeds originated at pasture grasses introduced into northern Australia between 1947 and 1985. Of these, 13 are now major pests. Ironically, the CSIRO recently came to the conclusion that many native grasses provide better fodder than introduced most grasses anyway! The sad fact is that we are still introducing into this country plants which are becoming major environmental weeds. Why?!
Introduced for cattle grazing, Gamba Grass is rapidly becoming the worst weed in northern Australia. This grass, if left uncontrolled, is likely to create monocultures of habitat throughout tropical Australia, proving unfit for a variety of woodland and grassland species as you mention below. Besides the natural environment, the impact of this grass would also be disastrous for the rural economy as well. Many bird species, including Gouldian Finch, Chestnut-backed Button-quail, and Yellow-rumped Mannikin face extinction if the grass spreads over their habitats.
Gamba Grass is highly inflammable. According to the chairman of the Gamba Action Group, David Welch, a large gamba grass-fuelled fire near Batchelor in 2004 spread five kilometres in 25 minutes.
In an article which appeared in Nature Australia in the Spring of 1995, Tim Low, an environmental consultant, claims that:
“It is a national scandal that so many of our worst weeds were deliberately brought in. We may wonder why governments did not act long ago to stop the damage. The sad truth is that vested interests in government and industry oppose a tightening of the quarantine net. Indeed, the Quarantine Service is hamstrung by funding cuts, and many of its functions have been privatised – which is like handing over the nation’s defence to mercenaries.”
We all should become involved in waging war on weeds. Many weeds are spreading rapidly, establishing dense thickets that choke out native plants and dependent native fauna. Many infestations appear beyond control by chemicals or biological agents. Wise use of fire may be one way of alleviating the problem. Apart from damaging the natural appearance of an environment, weeds cost Australia $3 billion dollars each year and represent one of the conservation problems of the twentieth century. About $6 million has been spent trying to rid Kakadu of Mimosa pigra. Goodness knows how many millions of dollars and thousands of man hours have been spent clearing and trying to control blackberries in the southern States.
Serrated Tussock is a weed that looks quite innocent but it has the ability to replace pasture species without the landholder knowing until it is too late. It is useless to stock and not even rabbits are interested in eating it! It has infested 24,000 hectares of the Rowsley Valley just north of Bacchus Marsh and could cover 4.6 million hectares within a few years unless it is controlled now! A million dollar offensive is now under way. The infestation has now spread east to the Hume Highway.
Some of the worst environmental weeds in Australia include Rubber Vine (which is smothering riverine forests in north Queensland), Lantana, African Boneseed, Japanese Knotweed (Horsetails), Paterson’s Curse, Serrated Tussock, Blackberry, Gorse, Pond Apple, Salvinia, Bitou Bush, Willows, Prickly Pear, Mimosa and Bridal Creeper. The Australian Government has asked State and Territory governments to ban the sale of most of these weeds. Related to rhubarb, Japanese Knotweed comes from Mt Fuji where it tolerates cold temperatures and lava; its underground rhizomes can extend for up to 200 metres, allowing it to sprout on the far side of a road!
The worst weed-affected areas appear to be Cape York, the eastern seaboard (including the fringes of remaining tropical rain forests), the top end and Victoria.
Greg Keighery of the WA Dept. of Conservation and Land Management is quoted in the Bulletin as saying that “We can no longer assume the bush will be there forever, and in many ways it means we are losing our Australian identity”.
Even today, some councils still plant species listed in the DSE book mentioned above as environmental weeds when they could use suitable indigenous species along roadsides and in public parks, e.g. Canary Island Palms are still being planted even though they are escaping into bushland.
It is possible to release insects to help control some weeds but some nursery interests are opposed to the release of insects which could attack some of the weedy plants currently on sale.
Some Australian plants have become “weeds” overseas. In parts of South Africa vast areas have been covered by Australian wattles, and in the Florida Everglades Melaleuca is rampant in places. Back in Australia, some of our weeds are native to other parts of our country, e.g. Cootamundra Wattle should be regarded as a weed in the Murray Valley.
Problematic aquatic weeds are threatening to choke local waterways.
In August 2005, Gunbower area residents concerned with the profusion of weeds in channels and in Gunbower Creek organised a field trip and public meeting to discuss the extent of the problem. The invasion of aquatic weeds is far worse than many thought and the situation is deteriorating.
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An aquatic weeds expert with Goulburn Murray Water, Roger Baker, identified seven aquatic weeds which are of major concern:
Alligator Weed (Alternanthera philoxeroides)
Arrowhead (Sagittaria graminea)
Fanwort (Cabomba caroliniana) (America)
Dense Waterweed (Egeria densa)
Parrots Feather (Myriophyllum aquaticum) (Amazon Basin, South America)
Senegal Tea Plant (Gymnocoronis spilanthoides) (despite its name, native to Central and South America)
Yellow Water-lily (Nyphaea mexicana) (despite the species name, native to Europe)
Not yet widespread in our district, Alligator Weed is found in Bendigo Creek. But it has the potential to move down the creek and into the Murray River. It is sometimes a free-floating mat. This highly invasive weed chokes waterways, removing oxygen and causing siltation. It is a prohibited weed in Victoria.
Arrowhead is an emergent aquatic herb which spreads by seed, rhizomes and tubers. It is a particular threat to lagoons and backwaters, preventing waders and water birds from feeding. Unfortunately, in Victoria it is still legal to propagate, transport and sell this invidious weed!!! Unless politicians act to ban its propagation, distribution and sale, the situation may worsen. Whilst it may be impossible to eliminate this weed, control measures are imperative if channels are to remain usable. The best method of control is to dig up and the plant and deposit it safely above high water level. In the Gunbower system, there are 38 sites downstream of the headworks, two of which are actively spreading. This weed is spreading at the alarming rate of 20km per annum! Information to assist with the identification of Arrowhead can be found at Goulburn-Murray Water’s web site.
Cabomba (Fanwort) is a submerged aquatic herb which spreads easily and restricts water flows. Despite being a weed of national significance, it can still be propagated and sold in Victoria because it is a popular aquarium plant! There are infestations in Lake Nagambie and lake Benalla. For more information on Cabomba, see Goulburn-Murray Water’s web site.
Egeria is a submerged aquatic herb, usually rooted but sometimes floating. It forms dense mats which retard water flow. Only male plants appear to be wild, so no seeding takes place. But it is like the sorcerer’s apprentice’s broomstick, pieces breaking off to form new plants. Despite being banned in some States, it can still be propagated and sold in Victoria!!! Victorian landholders may ring Goulburn Murray Water for more information about Egeria.
Parrot’s Feather is a bright green freshwater herb which closely resembles our native Milfoil. It has the appearance of a tiny feathery conifer. It spreads from stem fragments, is invasive and difficult (impossible?) to control. Out-competing Milfoil and other natives, it is rampant in the National Channel near Gunbower. Sterile plants appeared a few years ago at the headworks of Torrumbarry Weir and appear to have been spread by anglers and birds. In four years, this weed has spread from covering 4ha to over 120 hectares! It is likely to reach the Murray. It is in Campbells Creek and threatening the Loddon River. Despite being a weed of national significance, it can still be propagated and sold in Victoria because, despite being very similar to native Milfoil in appearance, it is a popular aquarium plant!!! A beetle eats the plant only to water level; biological control seems unlikely to be successful. Information to assist with the identification of Parrot’s Feather can be found at Goulburn-Murray Water’s web site.
Senegal Tea Plant is a hardy aquatic herb which forms a mass of tangled vegetation, covering the water surface. White florets cover the plants in spring-summer. It spreads by seeds and broken stem fragments. Water flow is impeded. There are infestations in Lake Nagambie and in the Goulburn River. Information to assist with the identification of Senegal Tea Plant can be found at Goulburn-Murray Water’s web site.
Yellow Water-lily covers a lagoon along Matthews Road near Gunbower. Once a haven for waders and water birds, the lagoon can no longer sustain more than a handful of water birds, the weed covering the water surface and acting as a sediment collector. Consequent silting favours carp at the expense of indigenous fish. Victorian landholders may ring Goulburn Murray Water for more information on Yellow Water-lily.
Other weeds damaging local waterways include Persicaria and Water Hyacinth (Eichlorina). Umbrella Sedge (Cyperus eragrostis) is a problem in many drains and roadside gutters. Weeds of stream banks and littorals include Basket Willow, Bridal Creeper, Olive Trees, Boxthorn, various thistles, various introduced grasses and burrs, Horehound and Sweet Pittosporum.
Other threats. Leaving water levels in wetlands for too long and at too high a level is causing many local wetlands to deteriorate. They need to be allowed to dry out occasionally and kept at a level low enough to avoid the under mining of bordering trees. Many trees have died because of inappropriate water management practices. During the field trip, participants were shown an example of a degraded wetland, Longmore’s Lagoon. Water has been stored in the lagoon to meet the needs of 10 irrigation farmers. But the water has been kept at too high a level for too long and water flow has been restricted. Trees have died, trees have toppled down and blue-green algae has appeared in the stagnant water. Islands have disappeared and a a huge egret rookery has been all but abandoned by the birds.
After the field trip, participants met at the Gunbower Hotel to discuss steps which could be taken to control the deterioration of local waterways. It was resolved that local politicians be asked to ban the propagation, transport and sale of the above aquatic weeds. Unless action is taken, the cost of controlling aquatic weeds will escalate to the extent that water authorities may be unable to supply water to some irrigators.
External Link: Integrated weed management Weed Management Manual
The Weeds CRC has developed an Integrated Weed Management (IWM) Manual which encourages land managers to use the full range of control methods available and not rely on a single quick fix solution, such as herbicides alone.