Emergence of Sonchus oleraceus (common sowthistle) is favoured under zero tillage farming systems

The impact of different tillage treatments and seed burial depth on the emergence of S. oleraceus was evaluated in two fi eld trials. Increasing soil disturbance reduced S. oleraceus emergence and buried a greater proportion of seed below 2 cm than zero tillage or single operation tillage treatments. S. oleraceus seed emergence was greatest from depths of 0 and 1 cm, however a small amount emerged from a depth of 2 cm while no seedlings emerged from 5 and 10 cm depths. This study highlights that S. oleraceus emergence is favoured in zero tillage systems and that burial of seed through tillage below 2 cm will inhibit emergence of this weed

Biology and management of the 'take-all' weed, Polymeria longifolia (Peaks Downs curse), in cotton

Polymeria longifolia (Lindley) is a native species, behaving as a weed throughout many areas of the Australian cotton industry. Seeds are a relatively minor method of reproduction and dispersal compared with the production of underground rhizomes, which are concentrated in the top 40 cm of the soil profile but found to depth of at least 1.5 m. These rhizomes may be dispersed by cultivation and their success in producing new plants is directly proportional to increasing fragment size. Polymeria longifolia grows concurrently with the cotton crop making management very difficult. Active shoot growth of P. longifolia can occur at any time of the year in uncultivated areas and is probably linked to soil water status. Polymeria longifolia competes strongly with cotton, and is particularly detectable at soil moisture levels found immediately prior to irrigation. Although competition for major nutrients was suspected, no evidence was found in this study. Anatomical studies suggested there was some evidence that P. longifolia interfered with cotton through the production of allelochemicals but this requires further investigation. Densities of over 100 stems per square metre that are commonly found in weed patches reduced the yield of cotton lint and seed below 50%. Existing control measures based on herbicides and shallow cultivation are largely ineffective and inconsistent in their results, probably due to the large below-ground biomass of the weed. Shallow hand chipping appeared to stimulate shoot recruitment and it was hypothesised that herbicides did not translocate to a sufficient enough depth down the rhizome to prevent further shoot recruitment. The fmdings from this thesis suggest that intensive and repeated cultivation may reduce the size of P. longifolia infestations in the field

Factors affecting the sensitivity of chickpea ('Cicer arietinum') to isoxaflutole and its effect on nitrogen fixation

One of the major obstacles in growing chickpea ('Cicer arietinum) successfully is its poor ability to compete with weeds. Heavy crop losses are possible in weedy situations and the lack of registered post-emergence herbicides for broadleaf weeds reduces the options for weed management. In Australia, isoxaflutole at 75 g a.i. ha⁻¹ is registered for the control of several difficult-to-control broadleaf weeds [e.g. Indian hedge mustard ('Sisymbrium orientale'), sowthistle ('Sonchus oleraceus'), capeweed ('Arctotheca calendula'), prickly lettuce ('Lactuca serriola'), wild radish ('Raphanus raphanistrum'), turnip weed ('Rapistrum rugosum'), crassula ('Crasulla' spp.), medic ('Medicago' spp.), deadnettle ('Lamium amplexicaule'), and slender celery ('Ciclospermum leptophyllum')] in chickpea. However, there have been records of chickpea crop damage due to the application of isoxaflutole at the recommended rate. The main objectives of this study were to identify genotypes tolerant or sensitive to this herbicide, to determine the soil and environmental factors affecting the herbicide sensitivity of the genotypes and to examine the effect this herbicide has on nodulation and nitrogen fixation. Variety screening trials with a range of isoxaflutole rates have found that the chickpea genotypes Howzat, Yorker, 91025-3021 (desi types), FLIP 94-92C and S 95425 (kabuli tyopes) were more susceptible to isoxaflutole damage. In comparison, the desi genotypes 97039-1275 and Kyabra recorded very minor injury and can be regarded as the most tolerant. Other genotypes - Gully, Jimbour, Amethyst, Flipper, ICLL 87322 (desi types) and Bumper, FLIP 94-90C, GCN 133-2, IG 9337, IG 96220, Kaniva, Macarena, S 95342 (kabuli types) - are intermediate in their response to isoxaflutole

Ecology of 'Phyla canescens' (Verbenaceae) in Australia

'Phyla canescens' has invaded large areas of wetland and grassland on floodplains in Australia, particularly the Murray Darling Basin, where 'P. canescens' threatens the sustainability of internationally significant wetlands and the viability of grazing enterprises. The species was introduced into Australia from South America, where it is a common and widespread species of floodplains and waterways, particularly in areas subject to constant grazing, or otherwise continuously disturbed. It has been promoted in Australia and elsewhere as a hardy groundcover for its perceived aesthetic and soil conservation values. 'Phyla canescens' continues to be sold in the horticulture industry, invariably labelled "Phyla nodiflora"; a closely related species with which it is frequently confused. Both species are generally associated with waterways and floodplains and share a prostrate habit, with adventitious roots developing at each node along the numerous, intertwining stolons. Both species form dense mats to the exclusion of other vegetation. While 'P. canescens' has typically smaller features and inhabits more southerly, inland areas with heavy clay soils, the coarser "P. nodiflora" is more common in northern, coastal regions with sandy soils. The general lack of quantitative information on fundamental aspects of the life-history of 'P. canescens' is a substantial impediment to the development of sustainable and ecologically sound management protocols for this species, including biological control, and the communities which it invades. Experiments were devised to help address this information gap, the results of which are presented in this thesis

Precision pollination strategies for advancing horticultural tomato crop production

Global climate change and anthropological activities have led to a decline in insect pollinators worldwide. Agricultural globalisation and intensification have also removed crops from their natural insect pollinators, and sparked research to identify alternate natural insect pollinators and artificial technologies. In certain countries such as Australia the importation of commercial insect pollinators is prohibited, necessitating manual labour to stimulate floral pollination. Artificial pollination technologies are now increasingly essential as the demand for food grown in protected facilities increases worldwide. For tomato fruits, precision pollination has the ability to vastly improve their seed set, size, yield, and quality under optimal environmental conditions and has become financially beneficial. Like many crops from the Solanaceae, tomatoes have a unique self-pollinating mechanism that requires stimulation of the floral organs to release pollen from the poricidal anthers. This review investigates various mechanisms employed to pollinate tomato flowers and discusses emerging precision pollination technologies. The advantages and disadvantages of various pollinating technologies currently available in the protected-cropping industry are described. We provide a buzz perspective on new promising pollination technologies involving robotic air and acoustic devices that are still in their nascency and could provide non-contact techniques to automate pollination for the tomato horticultural industry

Ecology and Management of Non-Native 'Poa Annua' on Sub-Antarctic Macquarie Island

Invasive species pose one of the greatest threats to the Antarctic region and consequently control is a priority to managers. To date, all successful eradications of vascular plants in the sub-Antarctic and Antarctica have been on small, restricted populations. Eradication or control is more difficult for widespread species, largely due to established seed banks. Information on the biology of the target species and the efficacy of control can increase eradication success. It is also important to assess the impact of control on non-target species. One widespread invasive species in the Antarctic and sub-Antarctic under consideration for control is the grass 'Poa annua'. For any potential eradication or control programs to be successful, information is required on the species' ecology and response to control. Therefore with the aim of informing future management of 'P. annua', my thesis focused on quantifying the ecology of 'P. annua' on Macquarie Island and assessing the efficacy of physical and chemical control. This included assessing the impact of control on native plant species, and the mobility of glyphosate in Macquarie Island soils and potential off-target impacts. I found that 'P. annua' plants showed a perennial lifecycle, a common survival mechanism for sub-Antarctic plants, and they displayed considerable variation in growth forms across environmental gradients. 'Poa annua' plant size and seed banks varied across Macquarie Island in response to 'P. annua' cover and environmental variables. Larger plants and denser seed banks were found at low elevation sites with high 'P. annua' cover, high animal disturbance and deep, sandy soils. The high cover of 'P. annua' at these sites also suppressed native species diversity. Conversely, at high altitude, exposed sites with low 'P. annua' cover and shallow soils, 'P. annua' plants were small and seed bank densities were low or non-existent. Less than 3% of buried seed remained viable for two years. Plants from all sites allocated most of their biomass to root material (60-80%), likely to enhance persistence

Morphological and molecular characterisation of 'Echinochloa' species in the northern grain region of Australia and implications for weed management

Barnyard grasses ('Echinochloa' species) occur as major summer weeds in farming systems of the northern grain region (NGR) of Australia. Farmers report difficulty in achieving effective control of 'Echinochloa' using current management practices, with varied levels of success being reported. This study was undertaken to identify what species were present in the farming systems of the NGR, and to investigate if the varied levels of control could be attributed to morphological variations and/or the genetic diversity present within populations. It is important to identify correctly the 'Echinochloa' species present in order to achieve better control and reduce the current threat of glyphosate resistance evolution in these weeds in the NGR. This study commenced at the end of 2004 with field surveys being undertaken at three major cropping centres of the NGR; Wowan (central Queensland), Dalby (southern Queensland) and Narrabri (northern New South Wales). Two species were identified as occurring in the NGR, 'Echinochloa colona' (L.) Link and 'Echinochloa crus-galli' (L.) Beauv.. 'Echinochloa colona' was the most widespread species accounting for 93 percent of the plants sampled. Both species were morphologically diverse across the region with 'E. colona' categorised into 20 growth categories and 'E. crus-galli' into six categories. The most common growth form in 'E. colona' was semi-erect to prostrate (50%) while the majority of 'E. crus-galli' plants were erect (84%)

Ecological studies of 'Hyparrhenia hirta' (L.) Stapf in northern New South Wales

'Hyparrhenia hirta' (L.) Stapf (Coolatai grass) is a summer active, C4 perennial grass, native to southern Africa and the Mediterranean region. In recent years its range has expanded rapidly and there are now populations of H. hirta in all states and Territories of Australia except Tasmania. It invades native grassy and open woodland communities, including roadsides and travelling stock routes, national parks and pastures. There is little published information on the biology and ecology of 'H. hirta' in the summer rainfall environment of northern New South Wales. This study aimed to increase our understanding of key aspects of the ecophysiology, population dynamics and community ecology of 'H. hirta' to assist in control and management

Longevity, growth and community ecology of invasive Poa annua across environmental gradients in the subantarctic

Poa annua is a cosmopolitan weed in turf grass. It is a widespread non-native species in the subantarctic and also occurs in the Antarctic Peninsula. It has highly variable morphology, longevity and reproductive capacity across both its invaded and native range. Little is known about the ecology of P. annua in the subantarctic, particularly its longevity, morphological variation across small spatial scales and competitive ability. We monitored individual P. annua plants on subantarctic Macquarie Island to assess their longevity; quantified morphology and biomass allocation across environmental gradients; and assessed community diversity indices in areas of varying P. annua density. We show that P. annua plants on Macquarie Island are perennial, and their morphology varies with elevation, animal disturbance and soil properties. At low altitude, coastal sites with high animal disturbance and deep, sandy soils, P. annua plants are larger and native plant diversity is low. Conversely, at high altitude sites P. annua plants are smaller and the diversity of native species is not reduced. This new information informs why P. annua is the most successful plant invader in the subantarctic and quantifies some key characteristics enabling an invasive species to function well beyond its natural range. Community ecology theory can also explain patterns in the ecology of P. annua on Macquarie Island