School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe codling moth in Williams pears : a report of an investigation into the problem in the Goulburn Valley, 1936-19( 1944)The codling moth (Cydia pomonella,L.) is the most serious pest of pears in the Goulburn Valley irrigation area. In the Shepparton, Kyabram, and Ardmona districts, there are approximately 3500 acres of Williams Pon Chretien pears grown principally for canning purposes. For some years past, the losses of pears due to the codling moth have been considerable. In 1936 it was estimated, by executives of the Northern Victoria Fruitgrowers' Association, that codling moth losses accounted for as much as 20% of the total pear crop from the area, that is, a loss of at least �20,000 per annum was being experienced by the industry. No investigation of the codling moth had ever been conducted in the Goulburn Valley; and, although a considerable amount of research had been done elsewhere on the control of the pest in apples, little information was available on combatting the codling moth in pears. Ward (1936) conducted a survey of the pear-growing districts of the Goulburn Valley and found that there was a complete lack of uniformity among growers as to the control measures being used against the codling moth. Having no precise information on the seasonal activity of the pest, growers were not In a position to apply their sprays at the correct time, nor was there an efficient spray schedule in general use. In response to a request from the Northern Victoria Fruitgrowers' Association, and with funds made available from a Commonwealth grant for research and advisory work in relation to the apple and pear industry, an investigation of the problem of codling moth in 'NEC pears was commenced in 1936 by the Victorian Department of Agriculture. For the first two years of the investigation, portion of the Oriental Peach Moth Laboratory at the Ardmona Cannery was kindly made available by the Council for Scientific and Industrial Research, and so facilitated a study of the bionomics of the codling moth under Goulburn Valley conditions.
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ItemAn investigation of potato gangrene in Victoria : including the identification and comprehensive study of the causal organism, Phoma foveata Foister and a comparison of the Scottish and Victorian isolates with P. eupyrena Sacc., P. solanicola Prill et Del. and Phomopsis tuberivora Guss et Fost( 1957?)In October 1963 attention was drawn to the possibility of an hitherto unknown storage disease of potatoes in Victoria. Diseased tubers if the variety ton ware brought to the Plant Research Laboratory, Burnley, from a property at Clarke's Hill, via Ballarat, and a pycnidial-forming fungus was isolated consistently from lesions by Anderson (1953). Later that month, apparently identical isolates were obtained from diseased tubers of two other varieties which were received from the same property. In consequence, an investigation of dry rots in storage was commenced in September, 1954. One of the original objectives was to determine whether this pycnidial-forming fungus was a causal organism of tuber rot. As the investigation proceeded, it became evident that the fungus in question was responsible for a particular type of rot. In other countries similar types of tuber disease have been attributed to species of the Phomaceae. In the detailed study that followed, attempts were made to identify Victorian isolates with, or to distinguish them from, some of these other storage pathogens. As a result of the investigation, the pycnidial forming fungus has been identified as Phoma foveats Foister.. This fungus is responsible for the disease known as Gangrene of tubers in the British Isles. It has not been recorded previously outside that area. Although most of the work described in this report is laboratory in nature, one of the main aims has been to collect information which may may assist in determining an approach to the control of the disease.
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ItemStudies on the cereal cyst nematode (Heterodera avenae Woll.) in Victoria( 1973)Ten populations of the cereal cyst nematode (Heterodera avenge Will.) from the Victorian Mallee and Wimmera districts, were tested for their variation in pathogenicity, using a selected range of cereal species and cultivars as.indicators. The tests were made in a glasshouse between 1967 and 1969. Of the oats used, Avena sterilis and A.strigosa were resistant, but all other cultivars and species were susceptible to each of the populations. Two barley cultivars, Morocco, and Marocaine 079 were resistant to all populations, but all other barleys used were susceptible. None of the cultivars of wheat was resistant; the spring wheat cv. Loris was very susceptible. Rye cv. South Australian was resistant to all populations. The results indicate that a single biotype of H. avenge is present in Victoria. It appears to be more "aggressive" than any of the biotypes known in Europe. Two hundred and forty cereal species and cultivars (wheat, barley, oats, rye and Triticales) were field . tested for resistance to H. avenge at Sea Lake in the Victorian Mallee between 1966 and 1969. All wheats tested were susceptible to very susceptible, and all Triticales were susceptible. Two barley cultivars Morocco, and Marocaine 079 were resistant and two others moderately resistant. Avena sterilis and A. strigosa were resistant and fifteen cultivars of A. sativa were moderately resistant. Rye cv. South . Australian, posseses a high degree of resistance in contrast to European ryes. The systemic nematicides "Temik" and "Lannate", and the fumigant nematicides ethylene dibromide and dibromochloropropane, were tested for control of H. avenge in a field experiment with Wheat at Sea Lake in the 1968-69 season. All chemical treatments reduced white cyst production, and four of the treatments increased grain yield, and reduced nematode carryover. "Temik" (11 kg/ha broadcast), gave the best nematode control and more than trebled grain yield. "Lannate" (13'kg/ha broadcast) was almost as effective. Dibromochloropropane was an effective nematicide, but was phytotoxic at 56 1/ha. The systemic nematicides "Temik", "Lannate", "Nemafos", "Vydate", "Nemac ur P", and the contact nematicide "Mocap" were tested for control of H. avenge in field experiments with wheat; at Greenland Dam in the Wimmera (1969-70), and at Sea Lake in the Mallee (1969-70 to 1971-72). In one series of experiments all the nematicides were compared on a broadcast basis. All chemical treatments reduced white cyst production and nematode carryover. Plants from plots treated with "Temik" (9 kg/ha) were always cyst-free. "Mocap" when used at the same rate was severely phytotoxic. Grain from plots treated with "Temik" and "Lannate" at the higher rate (9 kg/ha) were analysed for the presence of chemical residues. No "Lannate" residues were detected, and "Temik" residues were less than 0.1 ppm. In a second series of experiments, a comparison was made of methods and rates of application of "Temik" and "Lannate". All broadcast nematicide applications, except those at Sea Lake in 1969-70, reduced white cyst production and nematode carryover. All nematicide applications with superphosphate in the drill row, except for "Lannate" 0.3 kg/ha at Sea Lake in 1971-72, also reduced white cyst production and nematode carryover. Significant grain yield increases were obtained in each experiment. "Temik" (9 kg/ha broadcast, and 2.2 kg/ha in the drill row) consistently gave the best control of H. avenge. Plants from plots receiving these treatments were always cyst-free. In all experiments "Lannate" dusted wheat seed provided little, if any, control of H. avenge. When used at comparable rates of application, "Temik" was a more effective nematicide than "Lannate".
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ItemDecline of river red gum (Eucalyptus camaldulensis Dehnh.) on grazing lands in Western Victoria( 1988)River Red Gum (Eucalyptus camaldulensis Dehnh.) is a common and extensively distributed tree in western Victoria. Widely-spaced stands of this species are a prominent feature of pastoral landscapes in that area. Many of these remnant stands are in a state of decline, with individuals being lost through deliberate clearing, senescence or the effect of rural dieback disease syndromes. This thesis reports on a study of the decline of one stand of E.camaldulensis trees growing on part of a grazing property near Buangor, in west-central Victoria. The rate of tree loss from agricultural land in the Buangor district was assessed from aerial photographs taken in 1947 and 1980. The average compounding rate of tree loss over that period was 1.1% p.a.. Rates of tree loss were greater from the remnant box-stringybark stands (1.9% p.a.) occurring in the district than from remnant River Red Gum stands (0.8% p.a.). The size and crown condition of all trees in the stand under investigation were assessed. Dieback-affected trees had relatively small and open crowns, that often had many dead branchlets and branches. The crowns of dieback-affected trees were largely of secondary or epicormic origin. Tree height and stem girth were not affected by contemporary crown health. The age of one tree was estimated by radiocarbon dating to be 440. ± 110 y B.P.. Detailed investigations of trees classified as either "healthy", "average" or "unhealthy" were undertaken. The amount of organic matter in soil declined as the quality of tree cover changed from "healthy" to "unhealthy" tree to open pasture. This change was probably linked with reduced additions of organic material through litterfall as tree crown cover deteriorated. The possible consequences of reduced litterfall and declining soil organic matter levels were that; (i) it may have disrupted biogeochemical nutrient cycling; and (ii) it may have increased the susceptibility of trees to root damage and other problems associated with animal traffic. Measurements of soil strength and bulk density indicated that soil under open pasture had been compacted, presumably by animal traffic. Soil under trees was harder during winter than soil under open pasture and was therefore less susceptible to puddling. Soil under trees was not as strong as soil under open pasture during spring and hence provided more favourable conditions for root growth. Investigations into the mineral nutrition of study trees found that "unhealthy" trees did not appear able to mobilize some macronutrient elements (N,P, K, Mg) to the same extent as "healthy" trees. The apparent nutrient deficiency may have been due to disruptions to the biogeochemical nutrient cycle as dieback progressed. The nutrient deficiency may exacerbate this disruption, since it was associated and possibly linked with delayed new foliage production in "unhealthy" trees and reduced area growth in that foliage. Measurements of leaf water potential, diffusive conductance and transpiration showed that atmospheric, rather than soil water deficits had the greatest influence on water relations in the study trees. The measurements showed that "unhealthy" and "average" trees did not greatly restrict transpiration during periods of high evaporative demand. "Healthy" and "average" trees transpired more water and assimilated more carbon than did "unhealthy" trees. Differences in gas exchange were due only to large differences in leaf area. Soil under "healthy" and "average" trees remained drier than soil under "unhealthy" trees and open pasture throughout the study period. However, there was little difference in soil water depletion during the summer, even though the annual pasture had died off. Measurements provide evidence of deep infiltration of water beyond plant root zones, particularly under open pasture and "unhealthy" trees. The healthier trees appeared to have a beneficial impact on the local water balance. Continued rural dieback and/or tree loss is likely to exacerbate disruptions to the local water balance that commenced with clearing for agriculture.
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ItemA study on damping-off in a regeneration mixed eucalypt forest( 1986)Although damping-off is known to cause considerable loss before and after emergence of seedlings in forest nurseries, little is known of its role in seedling mortality after direct seeding in artificial regeneration of mixed eucalypt forests. Findings reported in this thesis are the result of a survey for the presence of damping-off fungi in soils and dying seedlings, and tests of their pathogenicity to a range of eucalypts found in the Wombat State Forest of Victoria. This study was carried out in conjunction with a research programme established by the Victorian Department of Conservation, Forests and Lands to determine which factors govern the successful establishment of E. obliqua and E. radiata in three seed-bed types under five levels of overwood. Propagule counts for Pythiaceous fungi in burnt and unburnt soils from field experiment, plots prior to sowing indicated that the inoculum level was low and differed with levels of overwood retained following site preparation in summer (Chapter 2). Baiting the soils with E. sieberi cotyledons, apples or directly sowing E. sieberi seed in samples of the field soil showed that both burnt and unburnt soils were variably infested with Pythium spp., Fusarium spp., and Cylindrocarpon destructans. A small portion of the seed to be sawn in the field plots without any fungicidal pre-treatment was found to harbour a range of fungi, sane of which had the potential to inhibit germination of the eucalypts sown on the plots (Chapter 3). The fungi having this ability were however not isolated from damped off seedlings in the experimental plots. Field studies showed that the proportion of germinated seedlings killed as a result of damping-off was lower than that attributable to frost heave, droughting following freezing and insect damage (Chapter 4). Damping-off was found to be widespread over the entire study site and the rate of damping-off to differ with seed-bed type. Overwood density did not affect the disease level. Although Pythium spp. were responsible for most deaths, Cylindrocarpon destructans and Fusarium spp. also caused some mortality. Pathogenicity tests (Chapter 5) confirmed that the fungi associated with seedling mortality in the field can cause significant pre- and post-emergence damping-off in a range of eucalypts found at the study site. The fungi differed in their pathogenicity to the eucalypts and sane induced feeder root necrosis after the two leaf stage of seedling development. No differences in susceptibility to post-emergence damping-off were found between the tree species sown on the plots and others of economic importance in the forest. The overall findings and their implications for direct sowing as a management option in future field regenerations are discussed in Chapter 6.