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About Chilean needle grass | Research on CNG | Manager's Fact Pack | National Management | Upcoming Events | Feedback & Comments Manager's Fact Pack A range of control options for managing Chilean needle grass may be used depending largely on the size and density of the infestation, and the situation in which the infestation occurs. Suggested tools for integrated control include:
Prevention of spread Hygiene is the most important step in preventing Chilean needle grass spread and establishment. A list of practical steps for preventing the spread of Chilean needle grass are presented below. For areas 'clean' of Chilean needle grass, the greatest dispersal risk results from vectors created by man. Plant, equipment and material hygiene are of the greatest importance to prevent such spread, followed by controls over the movement of livestock. The following list of preventative steps from Liebert (1996) may assist land managers to keep Chilean needle grass from infesting their land:
Chemical control No herbicides are currently registered for the control of Chilean needle grass in Australia. Permits may, however, be obtained for some herbicides from the appropriate State/Territory organisations (Table 1). Controlling Chilean needle grass with herbicides should only occur with a full understanding of the limitations and risks involved, and as part of an integrated weed management program. Some general pasture restoration herbicides have been used successfully against Chilean needle grass but cannot be recommended until appropriate data have been obtained to enable the product to be registered by the chemical companies and the Australian Pesticides and Veterinary Medicines Authority. Table 1: Where to go for information on the chemical control of Chilean needle grass.
Where established infestations of Chilean needle grass occur, the management goal is to maintain the canopy cover of more desirable species so as to inhibit the establishment of seedlings. It is, consequently, not recommended to blanket spray large areas, as desirable species will also be killed and seed supplies of desirable species may not be inexhaustible as those of Chilean needle grass. If the main objective is to increase seedling emergence as a way of reducing the seedbank, baring the ground with herbicide applications over prolonged periods would result in lost pasture production and damage to the soil. In Australia, chemical topping is being used successfully to reduce the seed set of problem weeds such as Capeweed (Arctotheca calendula), Barley grass (Critesion histrix) and Brome grasses (Bromus spp). Chemical topping involves the application of sub-lethal rates (around 10% of recommended rate for total control of pasture) between early seedhead emergence and early flowering. As Chilean needle grass is unpalatable once it goes into flower, but can produce good feed during its vegetative phase, chemical topping trials are currently investigating if similar results can be achieved for this weed. Research from Australia and New Zealand has shown that chemical topping increases sugar levels, metabolisable energy and crude protein in treated seedheads, thereby improving palatability and encouraging stock to graze off seedheads. It should be noted that repeated use of one herbicide might result in the development of herbicide resistant populations. For example, at Waipawa in New Zealand, dalapon was repeatedly used till Chilean needle grass resistant populations developed. Grazing management Although palatable in its native country, Australian infestations of Chilean needle grass develop large numbers of unpalatable flower stalks during the summer months that are actively avoided by stock. In large established infestations, grazing strategies are aimed at making the grass more palatable to stock. In South America, Chilean needle grass is considered to be an important high value winter feed for stock. Conversely in Australia, once the plant enters into the summer reproductive state, the production of seed heads and ultimately a flower make it unpalatable to stock. These flowering stalks persist on the plant for several months, then fall to the ground where they form dense mats that shade the underlying pasture. Gardener (1998) suggests that once Chilean needle grass is established in a pasture, its successful biological traits ensure that it will remain a component of that pasture. Management strategies that remove flowering stems are necessary to maintain pasture productivity in such situations. Cell grazing is a management strategy that can remove the flowering stalks of Chilean needle grass and give more desirable pasture plants a competitive advantage. This system of grazing involves high stock densities in a limited areas to reduce selective herbivory, forcing animals to eat bulk material and trample flower stalks adding organic matter to the soil, opening up the canopy and thereby encouraging recruitment of preferred pasture. Gardener (1998) reports that a cell grazing system was successfully demonstrated at a site in Glen Innes. High stock densities of Hereford cross cattle and merino sheep for short periods was shown to remove the bulk of summer Chilean needle grass stalks produced by May, allowing the pasture to become more productive for the following six months. Mechanical control Where infestations are new and limited, hand weeding or 'grubbing' can prove a very effective way means of control. It may also be the one opportunity land managers have to eradicate the weed, so ensure that hand weeding is carefully carried out. Slay (2002c) recommends digging out the entire plant to at least 15 cm deep and 40 cm in diameter, placing the plant and soil in a 'hole-proof' sack immediately (ie. not allowing the plant to dry out in the paddock), and then dumping the sack in a deep offal hole or incinerating the sack in a large hot fire. The procedure should be repeated for any new plants that are discovered through regular site inspection. Mowing or slashing of seed heads is a common way of reducing Chilean needle grass seed production and its nuisance to stock. However, there are limitations with this method of control. Such techniques can effectively disperse stem seeds if hygiene is not maintained. Machinery and vehicles should, therefore, be decontaminated in the paddock of use prior to moving elsewhere, and clippings should be disposed of appropriately . Timing is also crucial, as early mowing may allow for further development of seed heads while late mowing may not prevent seeds from ripening on the cut stem. Chilean needle grass should not be mown for hay. Fire is potentially a useful tool to weaken mature plants and reduce seed production. However, Chilean needle grass produces basal cleistogenes that occur below the ground surface and may allow for rapid replacement of parent plants after fire. Cultivation Cropping may be an option for the control of Chilean needle grass on arable land. Establishment of a competitive pasture or other crops may be an effective control option on arable land, where the aim is to control Chilean needle grass and deplete the soil seed bank. Sowing of crop plants usually occurs in spring/autumn, thereby producing a dense sward of plants in autumn/early winter to prevent Chilean needle grass seedlings from establishing. Shallow cultivations will encourage germination of Chilean needle grass seed, and this may be practised until the seed bank is eliminated. Chilean needle grass seedlings that germinate during any cropping regime, must be prevented from flowering by integrating either chemical control or very heavy grazing. Biological control A biological control program has been initiated to identify pathogens in South America that only attack Chilean needle grass and can be safely introduced and released into Australia. An application was put to the Australian Weeds Committee to declare Chilean needle grass as a target for biological control. NSW Agriculture requested a survey of land managers attitudes to Chilean needle grass be undertaken. The Victorian Department of Primary Industries undertook a survey of 1000 land managers impacted by Chilean needle grass in Victoria, NSW and the ACT and received 160 responses. 89% supported biological control of Chilean needle grass, 8% were undecided and only 3% were against biological control. Only 3% believed Chilean needle grass to be a beneficial plant yet most of these people supported biological control. As some land managers believed Chilean needle grass to be a beneficial plant, it was recommended that Chilean needle grass be put through the Biological Control Act. Surveys of pathogens attacking Chilean needle grass in South America have identified three pathogens showing potential for biological control. These are a rust, Puccinia nassellae, a smut, Ustilago sp. and a Corticiaceae basidiomycete fungus. Due to difficulties in culturing the fungus and the extremely low infection rates by the smut, the program is now concentrating on host specificity testing of the rust Puccinia nassellae. Permits were obtained from the Australian Quarantine and Inspection Service to import P. nassellae into Australian quarantine facilities. However, as no Australian biological control facilities currently meet Australian PC4 standards and it would take considerable time and money to get a facility to PC4 standards, the host specificity testing program has now been redirected to Argentina. The life cycle of P. nassellae on both N. trichotoma and N. neesiana is proving to be complex. No telia have been recorded on P. nassellae attacking N. trichotoma. Only uredinia, the repetitive stage of the rust, have been found in the field, rendering it impossible to prove beyond doubt the nature of the life cycle. Nevertheless, field observations would indicate the rust is autoecious. If P. nassellae is autoecious it would make the fungi more stable as there wouldn't be a sexual 'crossing' stage in its life cycle. Both uredinia and telia have been identified on N. neesiana. As yet, no infection of N. neesiana has occurred from basidiospores germinating from the telia. This suggests that either: 1. There is an alternative host (not yet identified); 2. The telia stage is becoming redundant and the P. nassellae is becoming autecious like P. nassellae on N. trichotoma; or 3. The conditions or growth stage of N. neesiana were not correct for basidiospore germination on N. neesiana. These possibilities are being investigated. Preliminary host specificity testing in Argentina has shown that P. nassellae from two out of four N. trichotoma accessions, is capable of infecting the Australian native grass Austrostipa aristoglumus, albeit at a much lower infection level than N. trichotoma. Interestingly, A. aristoglumis was also infected by the powdery mildew Blumeria graminis. No stipoid grasses are found infected with powdery mildew in the field in Argentina. Infections are quite common on other grasses such as Bromus spp. and Avena spp. One possible reason for A. aristoglumus observed susceptibility to these pathogens could be its lack of exposure to them. Additional tests need to be undertaken to determine if A. aristoglumus plants previously infected with P. nassellae will again become infected. No off target attack was observed from P. nassellae on any of the N. neesiana accessions tested. Results show that Australian N. neesiana is susceptible to infection by P. nassellae. Special Note: Manging Chilean needle grass in conservation situations Chilean needle grass is impacting indigenous open grassy communities that contain many threatened species. However, before embarking on a control campaign, it is imperative for land managers to note that there are management practices deemed suitable for the control of Chilean needle grass in agricultural settings that have potentially devastating impacts on conservation values. There is a very high potential for Chilean needle grass to impact upon biodiversity values in south-eastern Australia, due to the ability of the weed to invade extremely threatened grassland and grassy woodland communities. Although land managers may be eager to control this tenacious weed, they must exercise caution. Hocking (1998) highlights that there are some current and proposed land management practices for the control of Chilean needle grass that have potentially negative impacts on the biodiversity value of grassy communities: Ploughing Ploughing of areas that have not previously been ploughed may lead to the demise of significant conservation values. Soil disturbance is known to be a key threatening process, also exacerbates weed invasion from soil seed banks. Healthy grasslands can have a good resistance to weed invasion, yet the dangers of ploughing, even if associated sowing with indigenous species is planned, will likely further endanger the community. Herbicides Broadscale use of herbicides is a key concern for conservationists. Some herbicides can decimate entire populations of threatened plant species, and lead to irreversible weed invasion similar to the process of invasion caused by large scale soil disturbance. Ploughing and herbicide application could remove desirable competitive plants and produce ideal conditions for Chilean needle grass seeds to germinate. Nonetheless, the appropriate use of herbicides can prove an important tool for conservationists, and due to the need to minimise soil disturbance, various herbicides have been successfully used for the selective removal of Chilean needle grass in conservation remnants. Such selective removal might include the edge of a remnant that has low biodiversity values. Extreme caution must be exercised to avoid damage to indigenous forb species. Tree planting Tree planting for the control of serrated tussock has been widespread, yet the effectiveness of this technique is largely unknown. Planting out infested areas may further reduce conservation values if trees or shrubs are planted over areas containing significant indigenous forbs that require an open habitat. Furthermore, Chilean needle grass appears to tolerate shaded situations. For further information, please refer to the paper by Hocking (1998). Dr Colin Hocking is a Senior Lecturer at Victoria University of Technology, and has and continues to work on several projects investigating control options for Chilean needle grass in conservation settings.
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