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    A study of the susceptibility to Dalapon of four common pasture grasses : a thesis presented at Massey Agricultural College in part fulfilment of the requirements for the degree of Master of Agricultural Science in the University of New Zealand
    (Massey Agricultural College, 1959) Lawson, H. M.
    One of the more important developments of recent years in New Zealand agricuture has been the introduction of herbicides selective against grass species. Originally intended for the control of grass weeds in arable crops these herbicides have proved capable of being utilized in many other aspects of farming practice, the most spectacular of which is 'chemical ploughing'. This popular name has been coined to describe the process whereby pastures may be improved with the aid of herbicides on land which cannot succesfully be cultivated by conventional means. Extension of this technique to land which is only accessible to the aeroplane is being investigated by Blackmre (1958) and the preliminary reports suggest that 'chemical ploughing' may be a useful aid to aerial top-dressing and oversowing. Every new development, however striking, must satisfactorily blend with or replace existing practice before it becomes generally accepted. Many problems of practical application require solution before recommenbdations can be made to farmers and there are at present under investigation in field trials throughout the country. At the same time a thorough knowledge of the properties of the herbicides and the factors affecting their efficiency under a wide range of field conditions is essential. Where herbicides are applied to a mixed population of plants, as in a pasture, it is desirable to know, within fairly narrow limits, the tolerance of each constituent species. The experiments reported in this thesis were undertaken to investigate the susceptibility of some common pasture species to dalapon, the most important of the selective grass-killing herbicides involved in 'chemical ploughing' and associated techniques.
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    Some physiological effects of the herbicide bromacil (5-bromo-3-sec-butyl-6-methyluracil) on Asparagus officinalis L. : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science at Massey University
    (Massey University, 1985) Balasingam, Godwin
    The root-absorbed, photosynthesis-inhibiting herbicide bromacil (5-bromo-3-sec-butyl-6-methyluracil) was applied in sand culture to tissue-cultured 18-month-old Mary Washington 500W clone of Asparagus officinalis L. grown under controlled environmental conditions. Dose-response characteristics were determined and ED₂⁰ and ED⁵⁰ values computed by regression analysis for several parameters for asparagus plants exposed to a single application of 0, 2, 4, 8, 16, 32, 64, 128, 256, and 512 p.p.m. bromacil in non-draining pots. The results of this initial broad spectrum studies revealed a drastic decline in visually assessed foliage damage score, shoot growth and root fresh weight, and an increase in shoot death at relatively low concentrations. Good dose-response characteristics were obtained, and time-course data showed that the rate and severity of effects increased with increasing dose. The ED⁵⁰ values 18 days after treatment were: visually assessed damage score, 2.7 p.p.m.; shoot growth, 25 p.p.m.; shoot death, 4.6 p.p.m.; and root fresh weight, 2.1 p.p.m. A catalogue of colour plates showing visual phytotoxic effects was compiled. The injury symptoms observed were: yellowing of cladophyll tips followed by bleaching with the effects extending towards the base, cladophyll tipping and progressive cladophyll death leading to shoot death. Equal increment dose-response experiments were conducted at 0, 2, 4, 6, and 8 p.p.m. bromacil, using a portable fluorometer (Model SF-10) to obtain fluorescence emission measurements. The results showed a dramatic decline in the initial rise in fluorescence yield from the cladophyll tips 156 hours after treatment. The ED⁵⁰ value was computed to be 2.3 p.p.m. Fluorescence emission measurements from cladophyll tips from excised shoots placed in bromacil solution at the same concentrations showed a dramatic decline in fluorescence yield within 17 hours indicating that uptake and translocation was more rapid without the roots. No significant changes in chlorophyll a, chlorophyll b and total chlorophyll concentrations, as determined by 80% acetone extraction technique, were evident in the samples in which a dramatic decline in fluorescence yield occurred. The results of this study, conducted under controlled environmental conditions, showed that the asparagus clone tested readily absorbed bromacil through its roots and translocated it to the foliage causing severe initial damage to the photosynthetic apparatus followed by detrimental effects on other parameters such as shoot growth, root fresh weight and shoot death. Even at a bromacil concentration of 2 p.p.m. the asparagus plants were found to susceptible to herbicide damage.
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    Responses of Rumex obtusifolius L. to several 'hormone' herbicides : being a thesis submitted in partial fulfilment of the requirements for the degree of [Master of] Agricultural Science, University of New Zealand, Massey Agricultural College
    (Massey Agricultural College, 1952) Templeton, John Keith
    Weeds have been a problem to man ever since he began to till the soil. Their presence is a factor lowering yield and increasing the cost of production of almost every economic crop. Weed eradication and control measures therefore, are bound to loom large in the management of crops at various stages throughout their growing period. Following upon such discoveries as those of Slade et al (1) and Mitchell and Hamner (2) that synthetic growth-regulating substances possessed properties capable of causing violent and often fatal disturbances to plant growth, new and effective methods of destroying undesirable species were developed. In fact, it can be said that the whole thought and practice of weed control was revolutionized by the promotion of certain practical aspects proceeding from the rapidly accumulating knowledge of plant-growth substances. [FROM INTRODUCTION]
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    Aspects of resistance to phenoxy herbicides in nodding thistle (Carduus nutans L.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1992) Harrington, Kerry Charles
    A nodding thistle (Carduus nutans L.) population had been reported from Argyll in Hawkes Bay, New Zealand, which had poor susceptibility to MCPA and 2,4-D. Plants from the Argyll population were grown beside another Hawkes Bay nodding thistle population in a glasshouse and their dose response curves for MCPA were compared in three separate experiments. The Argyll population was significantly less susceptible to MCPA in all experiments, though the magnitude of resistance varied between experiments from 5-fold to 14-fold. When grown beside each other in the field, the Argyll population was 7 times more resistant to MCPA than the other population. A range of other herbicides was applied to the Argyll nodding thistle population. Cross-resistance was detected for 2,4-D and MCPB, but no significant decreases in susceptibility were detected with mecoprop, clopyralid, picloram, dicamba, paraquat/diquat or glyphosate. A significant reduction in susceptibility to tribenuron-methyl was measured in a field experiment, but this difference was not apparent when the experiment was repeated in a glasshouse. The cross-resistance to MCPA, MCPB and 2,4-D meant selective control of nodding thistle at Argyll in clover-based pastures was now very difficult to achieve. Nodding thistle populations from 20 Hawkes Bay and 7 Waikato properties were tested for resistance to MCPA, and significant levels of resistance were detected in 14 of these populations. Interviews of property owners indicated that resistance had developed where 2,4-D or MCPA had been applied annually for many years, whereas properties without resistance had been sprayed less regularly. Resistant and susceptible nodding thistle seedlings were grown together at a 1:1 ratio under conditions of nutrient stress to determine whether herbicide-resistant nodding thistle plants are less competitive than normal. No difference was detected between the resistant and susceptible biotypes used. Under some conditions, susceptible plants were more likely to have high trichome densities on their leaves, but this trait was found to be too variable and not correlated closely enough with herbicide susceptibility to be useful in distinguishing between resistant and susceptible biotypes. Significant differences in susceptibility to MCPA were maintained between resistant and susceptible biotypes even when leaf surfaces were damaged to allow better foliar penetration of the herbicide, or when herbicide was applied to plants via the root system. Thus the mode of resistance did not appear to involve difficulties with foliar uptake. Studies with radiolabelled 2,4-D confirmed that resistance did not relate to poor leaf penetration. These experiments indicated that 2,4-D was broken down more rapidly in resistant plants. Other findings were that 2,4-D or its metabolites were released in greater quantities from the root systems of susceptible plants, and that herbicide molecules were more difficult to extract from the interior of susceptible plants, possibly due to increased binding. Reasons why resistance to phenoxy herbicides has developed in nodding thistle are discussed, and techniques for controlling resistant populations selectively in pastures and preventing further resistance from developing are also analysed.