By Mr John C Kerin AM FTSE
Australia has been invaded by foreigners and exotics for many years. Many of these invaders are of South African, South American and Mediterranean origin. Border protection has failed as the globalisation of weeds continues its onslaught. It is ironic that the Australian Government is spending nearly $600m to combat the threat of Foot and Mouth Disease in cattle at the border (and other threats, including some effort at detecting weeds), but only spending a fraction of that on a widespread and insidious menace which is already here. The most recent funding to support additional work on weeds amounts to about $7m in the current year. Many of these weeds are not ‘lost causes’ but still viable targets for improved control. Great progress has been made recently in managing two major threats, bridal creeper in southern Australia and rubbervine in Queensland, by biological control and improved use of fire.
Water use, land degradation, salinity amelioration and biodiversity decline are subjects well identified at all levels of government in Australia (even if not courageously, cohesively nor properly pursued). The general public is becoming more aware that these subjects provide crucial policy challenges. It is to be hoped that we may see more progress in attempts to better manage all the issues associated with them (hope springs eternal).
In contrast, the question and cost of weed infestation in Australia is one that does not achieve the same prominence. While it is becoming increasingly important in the minds of some at the level of policy and opinion making, the national response to the problem is vastly under-resourced. For the most part, weeds have not yet arrived on the national policy agenda let alone in the perceptions of those in our wider society.
A simple definition of a weed is a plant growing in the wrong place or where ‘we’ don’t want it. While this definition may suffice, not all of us see the same plant as a problem and the impact on our natural environment goes well beyond an impact by way of replacement of native species. As examples of this, graziers continue to plant grasses that threaten nearby eco-systems. ‘Benign’ species that graziers and farmers have been encouraged to grow are eliminating our native grasses and while being good for grazing, they are proving to be disastrous for natural bushland (eg gamba grass, hymenachne, mission grass and buffel grass). While politically active environmentalists worship or hug trees (to grow membership?), they don’t seem all that concerned about plants such as bridal creeper, which are destroying the diversity of swathes of bushland. This can be partially explained by the fact that general public doesn’t recognise our more serious weeds (and weeds are therefore harder to raise as an issue), and that many conservationists may underestimate the threat of weeds because they are still green compared to mine sites and saline creeks.
Weeds are having a devastating affect on our national environment as well as on both production and productivity in our cropping and grazing lands.
As examples of this claim, it is estimated that blackberries now infest 8.8m and lantana 4m hectares in Australia, much of it on public land (more area than that estimated to be affected by dryland salinity in the next 20 years). In cereal cropping, 5.9m hectares is infested with unwanted rye grass, 2.7m hectares with wild radish, 2.4m hectares with wild oats and 1.5m hectares with spiny emex. More than 2,700 plants from overseas have become established in Australia. At least 200 of these provide real problems, and each year another ten or so candidates take root. Weeds now make up 16% of Australia’s wild plant species.
Studies have shown that the direct cost of weeds in winter cropping (mainly in the wheat industry) is estimated to be of the order of $1,200m per annum or $67 per hectare (with a range of from $38 to $96 per hectare). The losses from weeds in cropping, pastures, horticulture and non-agricultural areas now probably exceed $3.5b per annum (the indirect cost for the natural environment is hard to estimate). However, it goes beyond measurable costs. Agriculture is marked by ongoing, continual scientific, technical and engineering innovation. Technology is now driving a precision farming revolution. To keep tillage to a minimum requires precision but it also requires that weed infestation does not clog up the gear and thwart soil and land friendly practices and productivity gains – hence, for example, the importance of addressing rye grass resistance to glyphosate in WA cropping country.
A list of Australia’s worst weeds was released by the Australian Government in 1999. The Weeds of National Significance (WONS) included consideration of both socio-economic and environmental issues; most are both environmental weeds and pests in agriculture. The WONS list includes both weeds with already wide distributions and others that are predicted to have massive distributions if left unchecked:
- Alligator weed- aquarium plant now threatening flow diversity in rivers
- Athel pine – shelter tree threatening water courses like the Finke river
- Bitou bush and boneseed – threats to dune zones and southern native forests
- Blackberry – fruit vine choking the bush
- Bridal creeper - garden vine that chokes ground cover in the Mallee
- Cabomba – aquarium plant now in rivers
- Chilean needle grass – unpalatable pasture weed
- Gorse- once used for fences, now barricading the bush
- Hymenache – wetland grass
- Lantana - garden shrub choking the bush
- Mesquite – fodder and shelter tree
- Mimosa bush – botanic garden escape
- Parkinsonia – shelter tree
- Parthenium weed – allergy threat
- Pond apple – a tree that threatens mangroves
- Prickly acacia – shelter tree
- Rubber vine – a garden plant that is poisonous to stock
- Salvinia – aquarium plant now choking streams and ponds
- Serrated tussock – unpalatable pasture grass
- Willows (Salix species)- chokes river banks.
All but four of these weeds were introduced to Australia or spread deliberately. The Indigenous Land Corporate concurs with these listings as being of concern on indigenous held land, but adds species such as Noogoora burr, the range of thistles, Patterson’s curse, horehound, mother of millions and ‘woody weeds’, all being familiar to most farmers and graziers.
Other highly ranked environmental weeds include:
- Para grass – pasture grass
- Buffel grass – pasture grass
- Water hyacinth – ornamental pond plant
- Aleman grass – pasture grass
- Reed sweetgrass – pasture grass
- Jerusalem thorn – shade tree
- Mission grass – pasture grass
- Blue thunbergia – ornamental vine
- Japanese kelp – accidentally introduced seaweed
All except Japanese kelp were brought to Australia deliberately.
Government agencies such as CSIRO, the Australian Quarantine and Inspection Services (AQIS) agriculture and state environmental departments, local government authorities and many community organisations have been fighting a lonely battle against weeds for some time. Yet an under-resourced AQIS and even parts of CSIRO have been criticised for allowing or encouraging so many plant introductions that have turned out to be weeds. The main weapons have been herbicides and biological control, but by the early 1990s a stage had been reached where there was less than a handful of full-time academics engaged in the teaching and researching of weed science. Courses in weed science were dying in our universities.
The CRC for Weed Management Systems (WMS) was established in 1995 and brought together some 140 researchers and educators drawn from nine member institutions.
Any education in the theory and practice of weed management had been fragmented and unco-ordinated at all levels. Although weed management for pastures and the main grain crops had been included in agronomy and crop management courses in a few universities, specialist weed management for other crops and natural eco-systems had generally only involved a lecture or two. Given the cut backs in university funding during the life of the CRC, one can only assume that in the absence of it the teaching of weed science would have further declined.
When Commonwealth funding of $12m for seven years was first granted to create the CRC, it was seen that not only was collaboration essential, but that to successfully embrace integrated weed management and to perform appropriate weed science required an injection of expertise. From a virtual standing start, the first priority was to encourage students into post graduate work on aspects of weed science. Success resulted with 34 PhDs, 2 Masters, summer scholarships for second and third year university students, more than 50 honours scholarships, and a new weed management subject with enrolments now totaling more than 135 people at four universities.
Another crucial decision was to devote funds, from the outset, for communication and adoption with the employment of three technical co-ordinators. Among many other tasks, these people have developed a series of best management packages for key weeds in the initial cropping, temperate pastures and national ecosystem programs. The publications output is extensive as are contributions to scientific and general publications.
The CRC for Weed Management Systems was reviewed given a seven year grant of $20.3m in January 2001. It is now titled the CRC for Australian Weed Management, reinventing itself by taking in tropical weeds and a broader range of strategies built on the experience of the earlier six years of work.
The CRC WMS had set a target to bring about a 10% reduction in the annual cost of weeds, estimated to be $3.0b per annum in 1995. An economic assessment of the benefit of only three projects in the cropping and pasture programs indicated internal rates of return of from 43 to 62% and, for one environmental weed, some 29%. There is little doubt that the $300m target figure was reached.
The value of the CRC has been recognised by the Grains Research and Development Corporation, who have been a major contributor since its inception. Plant Health Australia, the CSIRO and a range of departments and universities from nearly every State and Territory are now contributors. Globalisation has meant fewer and fewer multinational agricultural chemical firms whose representatives in Australia have been supporters of the work on integrated weed management, chemical resistance and better use of herbicides.
While education, training, communication and adoption were a priority from the outset, these were adjuncts to the main game of weed research. The initial program research areas were based on the straightforward categorisations of crops, pastures and natural ecosystems with general strategies of impact reduction and integrated management concentrating on key weeds as indicator species or those assessed as being of greatest cost to production.
Within the three broad research programs there was a commonality in sub-programs – ecology and population dynamics, biological control, herbicides, economics and decision support – with farming and grazing systems being specific to crops and pastures and impact assessment and ecosystem rehabilitation being specific to natural ecosystems. All projects and student topics flowed from these general sub-programs. PhD topics have been of the order of 24% on ecology, 21% on systems and decision support, 16% on herbicides, 12% on biological control, 9% on genetics, 7% on technical transfer and 11% on other subjects.
As experience grew, and as there is a commonality in the scientific and other topic areas, it was seen that more holistic/strategic approaches were needed. Hence, there is to be more concentration on incursion, systems and landscape scale focus in CRCAWM. There is no way Australia will ever get on top of every one of the 200 or so weeds of most concern!
Be this as it may, the fundamental areas of scientific inquiry need to continue to feed in to the more applied areas of research. There are many general and specific avenues of research that have been pursued but for the purposes of this article only a few will be selected for illustrative purposes. A reasonable selection would suggest genetics, ecology and population dynamics, biological control, herbicides and integrated weed management (which of itself involves decision support systems, modeling, remote sensing, survey techniques and prevention).
Much of the genetic work has been in the area of measuring genetic variation, finding resistant genes, identifying markers, and in finding competitive genotypes, in crops, weeds and biological controls. For example, a major study was carried out into assessing the gene flow from herbicide resistant to conventional varieties of crops and to crop relatives and vice versa. In the case of canola, pollen flow from resistant to non-resistant varieties was never detected above the 0.1% level. With respect to crossing with weeds, an experiment involving the assessment of 52.5 million canola seeds found only two hybrids. These findings have proven to be highly relevant to the debate on genetically modified organisms. As another example, strongly competitive crops would be a low cost weed management technique. In wheat, markers may be found to help introduce traits such as early vigour, leaf width and improved root patterns into Australian wheats from other varieties, thereby enabling plants to smother competing weeds.
Understanding population dynamics of weeds in their seed production and then coupling this with an understanding of factors that may affect vigour under various treatments has proved to be very effective. This has involved work on thresholds, longevity of seed banks and timing of intervention. Demographic databases for major weed groups have been identified for natural ecosystems. Without basic work on populations being carried out, modeling and integrated approaches to management are bereft.
There was a general view that no big ‘break-throughs’ were likely to occur in biological control. Experience, hard scientific work, and national and international collaboration has proved otherwise. The release of control agents requires very careful assessment. Introduction of agents is slow, and best results often occur in conjunction with the use of herbicides, fire, stocking rates, etc. The following is a brief list of successful organisms released, being tested or being developed. Some represent exceptional success.
- Rust and soil fungi on Bathurst Burr, Pattersons Curse, wild oats, blackberry, bridal creeper, various thistles, serrated tussock and Chilean needle grass.
- Mites on St John’s wort and Scotch broom.
- Various moths, seed flies, leaf rollers, psyllids, gall flies, weevils, leafhoppers, and beetles on horehound, Bitou bush, thistles, Pattersons curse, bridal creeper, Scotch broom and ragwort.
School children from 56 schools and 19 community groups now spread a leaf hopper and a rust fungus on bridal creeper in WA, SA, Victoria and Tasmania. Rusts and fungus work best with moisture periods and some moths work best in conjunction with a herbicide, eg, the plume moth on horehound in conjunction with 2, 4-D amine.
The work on herbicides is extensive and includes the use of bioherbicides and mycoherbicides. Bio-herbicides are those utilising a range of micro-organisms applied in high doses when the target plants are most susceptible to infection. Mycoherbicides are those using fungi. To deliver those herbicides requires that the spores on the weed surface retain sufficient moisture for the fungus to survive its dew period, ie, to establish. Two fatty alcohols and six polymeric gels were tested to enhance the delivery of these herbicides. In more conventional terms, herbicide investigations have been carried out into performance, efficacy, carry-over, dose rates, tolerance, targeting, interactions, timing of application, combinations, selectivity, rotations, novel mixes and systems and strategies alone or in combination with other weed killing approaches, eg, with fire, with grazing intensity, with biological control agents. Where high rates of herbicide are non-economic, work on low dose application has shown promise.
Integrated weed management requires the use of many overlapping areas of research and on ground involvement. It has been shown that perennial pastures can compete against annual weeds, and the tactics used are being demonstrated to land holders. Management options to control Patterson’s curse involving combinations of biological control agents (not affected by herbicides or grazing), active grazing management (including summer rest), and application of herbicide and fertiliser applications can provide better grazing if not restoration of perennial pastures. Similarly, long term suppression of silver grass and Chilean needle grass has been shown to be possible by rotational grazing regimes in combination with fertiliser application and the utilisation of herbicides at crucial control points.
The results of the now seven years of work are readily available, including published books and manuals. The future direction of the CRC WMS will be on landscape management and weed incursion and risk management. As an example of this, one task will be to develop strategies for managing weeds in three important weed prone habitats, viz rainforests, riparian zones and rangelands, addressing four major weed syndromes, namely, unpalatable grasses, aquatic weeds, invasive rangeland shrubs and bird dispersed weeds. It is clear that there are considerable environmental gains to be made if threatening incursions can be managed effectively before they become widespread. Early detection is essential. Targeted end user groups will be involved, hopefully leading to a national system and proven capability for rapid evaluation of and response to weed incursions. At this time we know little about the recruitment period for weeds and the CRC is looking at ways and means for the general public to identify small areas of escapes before they get out of hand. So on one hand, the CRC wishes to see some deliberate introductions screened and rejected, and on the other to look at what has been pitched over the back fence!
The battle against weeds in Australia will never be won but a least the enemy has been engaged and there are now enough trained people to engage in high levels of weed science and weed management. A concentration of effort in nation-wide collaboration has shown what can be achieved. This must inevitably lead to a higher public perception of the problem. Involvement of the community is being invited and promoted. With a bit of luck, there might even be a job or two in it for weed and weed related science areas once the costs of doing nothing new are understood.
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