Academic literature on the topic 'Nassella trichotoma'

Flupropanate (sodium 2,2,3,3 tetrafluoropropanate), a slow-acting lipid bio- synthesis-inhibiting herbicide, was recently registered in New Zealand as Taskforce (745 g/L flupropanate as the sodium salt) for the selective and long-term control of Nassella trichotoma (nassella tussock) in pastures. In five dose-response experiments in permanent hill pastures in Canterbury, conducted between 2012 and 2016, we measured the efficacy of the herbicide against established plants of N. trichotoma and its residual activity against recruiting seedlings. Mortality, as an average across the five sites, was 93% 1.5 years after applying 1.49 kg flupropanate/ha (the label-recommended rate), and 100% at 2.98 kg/ha. This indicates that an application rate higher than the label rate will be necessary for complete control of a N. trichotoma infestation. The presence of 1,000 and 6,250 visible seedlings of N. trichotoma/ha in the autumn 3.2 and 2.1 years after applying 1.49 kg flupropanate/ha (at a Greta Valley and Scargill site respectively) indicates that the herbicide’s soil residues had decayed within 12 months to a concentration lower than necessary to kill the germinating seedlings of N. trichotoma.

Nassella trichotoma (serrated tussock) is a hardy perennial grass weed that rapidly invades disturbed areas. Pasture competition is an important component of an integrated weed-management system for native pastures. This paper reports on a field experiment to ascertain the level of competition from native grasses for adult N. trichotoma plants. Native grasses prevented N. trichotoma plants from increasing in biomass and basal area when rotationally grazed or when grazing was removed and fertiliser was withheld. Smaller N. trichotoma plants (<500 mm2) were more likely to vary in size with very little change in larger plants. Flupropanate efficiently killed all N. trichotoma plants but caused considerable damage to perennial native species, resulting in an uncompetitive pasture dominated by broadleaf weeds.

Serrated tussock [(Nassella trichotoma (Nees) Hack. # STDTR] is a clump-forming, perennial, cool season grass. It is native to South America, where it occurs in Argentina, Brazil, Chile, Peru, and Uruguay. In the past century, it has been introduced to New Zealand, Australia and South Africa, and also occurs in small acreages in France, Italy, and the United Kingdom. Serrated tussock occurs in fields, wastelands, and pastures, but rarely in wet or shaded areas.

An experiment was conducted to determine the influence of time of grubbing in the late spring–early summer, panicle developmental stage at grubbing, and the presence or absence of roots on grubbed plants, on the initial and post-senescent viability of fruits of Nassella trichotoma in North Canterbury, New Zealand. The percentage of fruits viable, following desiccation of panicles removed from plants grubbed in the field, increased from 1% for panicles just beginning to emerge from the leaf sheath, to 49% for panicles fully extended at the time of grubbing. Similarly, as grubbing date was delayed from late November (late spring) until late December (early summer), fruit viability increased from 0.3 to 47%. Overall, 36% of the fruits were viable on panicles at the time of grubbing, increasing slightly to 47 and 44%, respectively, after a period of desiccation with and without the panicles being attached to the grubbed plant's root system. It was concluded that if recruitment of fruits of N. trichotoma to the soil seed bank is to be prevented in North Canterbury, plants must be uprooted before panicle extension. Delaying grubbing to when panicles are fully extended, while possibly enabling a higher percentage of plants to be detected and therefore destroyed, carries with it a high risk of permitting the recruitment of viable fruits to the soil seed bank.

Native perennial grass competition can substantially reduce the invasion of Nassella trichotoma (serrated tussock), a major perennial grass weed problem in south-eastern Australia. This paper reports on a field experiment that investigated the recruitment of N. trichotoma seedlings, and determined what level of native grass competition was needed to prevent establishment in the central-west of NSW. Grasslands that maintained >2 t dry matter (DM)/ha and 100% ground cover (measured in spring) prevented N. trichotoma seedling recruitment. Relatively small amounts of perennial grass (>0.5 t DM/ha measured in spring) resulted in mortality of N. trichotoma seedlings that had recruited earlier in the year, through the next summer. Flupropanate also markedly reduced native perennial grasses and substantially increased N. trichotoma seedling establishment 12 months after application. Rotational grazing to maintain adequate levels of DM was an important management tactic that prevented N. trichotoma establishment and survival.

Two Nassella species, Nassella trichotoma and Nassella neesiana, have significantly reduced the carrying capacity of Australia’s south-east rangelands and agricultural systems. It is, therefore, of considerable concern that four other Nassella species have also become naturalised in Australia, and are noted to share many of the ecological features of the two currently widespread species. This paper reviews the distribution, ecology, and impacts of all six Nassella species, which are currently naturalised in Australia, and makes recommendations toward a blanket Nassella control program. The review highlights observed similarities between the species, including the time of flowering, seed type, germination requirements, and growth morphology. These common factors support the possibility that an integrated Nassella control program could be designed to integrate good grazing management with cultural control methods, such as soil cultivation, fire, and native plant competition, with treatments being implemented prior to the common annual seed maturation period. Notwithstanding the success of these integrated programs, it is recognised that seeds of all species may remain viable in the seedbank for up to 12 years, meaning ongoing monitoring and management will be required. To develop even finer control programs, further research into the ecology of these Nassella species is recommended to determine any additional weak spots in these species’ defences, and to subsequently develop and apply novel integrated control methods that target all six species.

Nassella tussock (Nassella trichotoma) occurs most frequently in droughtprone grasslands in several areas of New Zealand where it is the subject of surveillance and/or regional management strategies The potential range of nassella tussock in New Zealand was estimated using a climate model developed from global distribution data (excluding the known distribution for New Zealand) The climate suitability of New Zealand for nassella tussock was estimated using a gridded climate dataset with a spatial resolution of 10 minutes of arc The model projections encompassed all areas of current occupation as determined from the records of ten Local Authorities and revealed vast tracts of land particularly in southern Canterbury and Otago which are currently climatically suitable yet unoccupied by the weed This map will enable regional authorities to recognise sites most at risk of invasion (those with high climatic suitability that are nearby current or historical infestations) and factor this into their management programmes

A previouslydeveloped model for a nassella tussock (Nassella trichotoma) population suggests that 97 of the seeds produced do not enter the soil seed bank To determine the extent to which seeds are lost from the soil surface an experiment was conducted over 1 year at three sites in North Canterbury pastures In January 2007 soil cores with intact pasture in opentopped containers were buried to ground level at each of the sites Three treatments (no seed 25 awned or 25 deawned seeds scattered onto the core surface) were applied The number of intact seeds recovered by monthly exhumation of cores declined linearly and at an average rate of 48 over the year Assuming the model is correct this rate of loss implies that only 5 of the seeds produced reach the soil surface and that 95 are therefore lost before deposition through wind dispersal or through predispersal predation

Temperate grasslands are globally important biomes, in that they (i) provide habitat for a wide diversity of species, (ii) sequester large stocks of carbon, and (iii) provide forage for important pollinators (Chapter 1). These ecosystems often fall within highly fertile areas, and consequently humans have come to depend on them to provide high quality forage for grazing livestock and land for agricultural development. Temperate grasslands are considered to be critically endangered on a global scale. The grazing industry relies upon healthy and productive grasslands for the production of a substantial proportion of human food products, however, when these systems incorporate unsustainable land-management practises, such as over-grazing and continual fertilisation with inorganic matter, has resulted in a significant decline in important native grass species. This has resulted in encroachment of unpalatable, noxious plants, which decrease the quality of available forage. One such noxious weed species, Nassella trichotoma, known commonly as serrated tussock, is having a significance impact on the constitution of temperate grasslands and grazing systems, globally, due to its unpalatability and competitive growth form. In order to return temperate grasslands to a fully-functional and a high-quality forage state, human intervention in terms of ecosystem restoration is required. The control of noxious species, together with the reintroduction and establishment of native species, is a critical step for restoration efforts with the return of native plant diversity, and the re-establishment of ecosystem services, such as habitat for higher trophic levels. This thesis reviews and overlaps the scientific disciplines of ecosystem restoration (Chapter 2), weed science relating to N. trichotoma (Chapter 3), and environmental management in order to provide solutions for controlling N. trichotoma in non-native grassland communities (Chapter 4). The effect of direct herbicide application, soil tillage, grazing exclusion, fire, and broadcasting native seeds for the control of this dominant weeds in a total of 13 different combinations is investigated. The experimental plots were surveyed over a four-year period and soil cores were collected over a three-year period to survey the seedbank density. It was found that the inclusion of fire significantly increased the establishment of the native broadcast species. Also, without the integration of fire or tillage, N. trichotoma recovered, and consequently was observed to be the dominant species in the final sampling period. To support the findings of Chapter 4, research into the seed longevity and seedbank persistence of N. trichotoma was undertaken in Chapter 5. It was found that less than 10% of the seeds were observed to be viable after 12 months of burial in field. In addition to this, the longevity of the seeds was determined by rapidly ageing the seeds through exposure to high relative humidity and temperature. This process determined that N. trichotoma produces transient seedbanks, referring to those that persist for 12 months or less, and therefore the seedbank would be reliant on new seed input annually to remain a competitive threat. This implies that management control of new seed fall is essential to prevent the reestablishment of the seed bank. The seedbank persistence for N. trichotoma is complicated by disturbance events such as fire. To investigate this impact, four different collection years; 2016, 2017, 2018, and 2019 were subjected to increasing heat (80, 100, 120, or 140OC) and time of exposure (1, 3, 6 or 9 minutes) by placing them into a temperature-controlled oven for the given treatment. It was found that only the 140OC treatment was significant for killing N. trichotoma, as detailed in Chapter 6. High moisture content (95%) increased the seeds sensitivity to radiant heat, with all tested temperature effective for killing this species. The seedlings were not killed by the tested treatments. Management implications and recommendations for the control of N. trichotoma in temperate grasslands (Chapter 7) include; (i) the use of herbicide in Autumn to prevent seed set in the following summer, and (ii) in addition to initial herbicide, use, subsequent fire treatment and broadcasting native seeds appear to provide ongoing competition against N. trichotoma reestablishment in treated areas. Further, high fire intensities, where the soil is heated to 140OC or more, can kill N. trichotoma’s seedbank and prevent its recruitment. In all cases of treatment, monitoring recruitment from the seedbank is recommended for up to one year after treating a site. This thesis suggests that localised eradication of N. trichotoma is achievable in as little as three years if (i) above-ground plants are treated, (ii) seedling recruitment from the seedbank is managed intensely within the first year, (iii) high densities of native grass is established to provide competition, and (iv) the addition of new seed is prevented.
Doctor of Philosophy

A 'spray and hay' method was developed which replaces the noxious weed serrated tussock (Nassella trichotoma (Nees) Arech.) with indigenous kangaroo grass (Themeda triandra Forrsk.) in partly disturbed remnants of western (basalt) plains indigenous grassland, a community listed as vulnerable to extinction. Investigations were carried out on Melbourne's north-west urban fringe. Refinements of the 'spray and hay' method resulted in low densities of other weeds amongst the newly established T. triandra swards. First steps in the method involved removal of weeds by slashing and follow-up treatment with either of the herbicides, glyphosate (as Monsanto Roundup®) or atrazine (as Nufarm Nutrazine®). These steps resulted in close to 100% kill of mature N. trichotoma plants. Greater than 98% replacement of N. trichotoma with T. triandra was achieved by thatching over herbicide-treated plots with seed-bearing T. triandra hay harvested from remnant grasslands and then removal of the hay several months later by either burning or physical removal. The type and timing of herbicide application, thatching and removal of thatch were found to be central for successfully establishing competitive densities of T. triandra seedlings and minimizing re-establishment of N. trichotoma and other weed seedlings. A treatment set involving: slashing weed biomass in summer (January), herbicide application in autumn (April) followed by thatching with seed-bearing T. triandra hay in winter (July) and removal of thatch in spring (October) produced the best results. Assessing the seed content of hay and germinability of seed prior to revegetation were also important for calculating the amount of hay laid and subsequent seedling densities established. The seed content and germinability of seed-bearing hay was found to vary markedly in samples harvested in three different years, across discrete remnant grassland sites and even within undisturbed grassland sites. Reasons for the success of the method, and why other variations are less successful are discussed, as is the wider application of the method for weed control and replacement with indigenous grasses in lowland grassland remnants.

A 'spray and hay' method was developed which replaces the noxious weed serrated tussock (Nassella trichotoma (Nees) Arech.) with indigenous kangaroo grass (Themeda triandra Forrsk.) in partly disturbed remnants of western (basalt) plains indigenous grassland, a community listed as vulnerable to extinction. Investigations were carried out on Melbourne's north-west urban fringe. Refinements of the 'spray and hay' method resulted in low densities of other weeds amongst the newly established T. triandra swards. First steps in the method involved removal of weeds by slashing and follow-up treatment with either of the herbicides, glyphosate (as Monsanto Roundup®) or atrazine (as Nufarm Nutrazine®). These steps resulted in close to 100% kill of mature N. trichotoma plants. Greater than 98% replacement of N. trichotoma with T. triandra was achieved by thatching over herbicide-treated plots with seed-bearing T. triandra hay harvested from remnant grasslands and then removal of the hay several months later by either burning or physical removal. The type and timing of herbicide application, thatching and removal of thatch were found to be central for successfully establishing competitive densities of T. triandra seedlings and minimizing re-establishment of N. trichotoma and other weed seedlings. A treatment set involving: slashing weed biomass in summer (January), herbicide application in autumn (April) followed by thatching with seed-bearing T. triandra hay in winter (July) and removal of thatch in spring (October) produced the best results. Assessing the seed content of hay and germinability of seed prior to revegetation were also important for calculating the amount of hay laid and subsequent seedling densities established. The seed content and germinability of seed-bearing hay was found to vary markedly in samples harvested in three different years, across discrete remnant grassland sites and even within undisturbed grassland sites. Reasons for the success of the method, and why other variations are less successful are discussed, as is the wider application of the method for weed control and replacement with indigenous grasses in lowland grassland remnants.

A 'spray and hay' method was developed which replaces the noxious weed serrated tussock (Nassella trichotoma (Nees) Arech.) with indigenous kangaroo grass (Themeda triandra Forrsk.) in partly disturbed remnants of western (basalt) plains indigenous grassland, a community listed as vulnerable to extinction. Investigations were carried out on Melbourne's north-west urban fringe. Refinements of the 'spray and hay' method resulted in low densities of other weeds amongst the newly established T. triandra swards. First steps in the method involved removal of weeds by slashing and follow-up treatment with either of the herbicides, glyphosate (as Monsanto Roundup®) or atrazine (as Nufarm Nutrazine®). These steps resulted in close to 100% kill of mature N. trichotoma plants. Greater than 98% replacement of N. trichotoma with T. triandra was achieved by thatching over herbicide-treated plots with seed-bearing T. triandra hay harvested from remnant grasslands and then removal of the hay several months later by either burning or physical removal. The type and timing of herbicide application, thatching and removal of thatch were found to be central for successfully establishing competitive densities of T. triandra seedlings and minimizing re-establishment of N. trichotoma and other weed seedlings. A treatment set involving: slashing weed biomass in summer (January), herbicide application in autumn (April) followed by thatching with seed-bearing T. triandra hay in winter (July) and removal of thatch in spring (October) produced the best results. Assessing the seed content of hay and germinability of seed prior to revegetation were also important for calculating the amount of hay laid and subsequent seedling densities established. The seed content and germinability of seed-bearing hay was found to vary markedly in samples harvested in three different years, across discrete remnant grassland sites and even within undisturbed grassland sites. Reasons for the success of the method, and why other variations are less successful are discussed, as is the wider application of the method for weed control and replacement with indigenous grasses in lowland grassland remnants.

Little published information is available on the levels of soil nutrients and soil moisture on remnants of native (Basalt Plains) grasslands. This study investigated the association of soil nutrients and moisture with stands of the native grass Themeda triandra (Kangaroo Grass) and the noxious weed Nassella trichotoma (Serrated Tussock). Both mature and immature (i.e. recently burnt) stands of T. triandra and N. trichotoma were investigated, on disturbed and undisturbed soil.