Masters Degrees (Agronomy)

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Browsing Masters Degrees (Agronomy) by Subject "Avena fatua L. -- Effect of herbicides on"

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    Glyphosate resistance in wild oat (Avena fatua L.)
    (Stellenbosch : Stellenbosch University, 2018-12) Matshidze, Mulweli Millicent; Pieterse, P. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Herbicide resistance is the ability of weed species to thrive and reproduce following applied recommended dosage of the herbicide that is toxic to the wild type. There is a world-wide occurrence in agriculture of weeds with high genetic diversity that have developed resistance to weed management, ryegrass (Lolium spp.) and wild oat (Avena fatua) included. Wild oats has developed resistance to commonly used herbicides which include clodinafop-propargyl, diclofop-methyl, fenoxaprop-P-ethyl, fluazifop-P-butyl, imazamox, iodosulfuron-methyl-sodium, sethoxydim, sulfosulfuron, and tralkoxydim in South Africa. There is an opportunity of using glyphosate to alleviate wild oats weed resistance problems when used in a pre-plant application. The herbicide has an uncommon mode of action but also has no wild oat resistance yet proven in South Africa. There are precautions to be considered when applying glyphosate since it is a post emergence herbicide. Most precise recommended dosage rates of herbicides can be developed by determining the effect of environmental factors, different location and plant growth of weeds on efficacy of glyphosate. The principle objective of the study was to determine the effective dosage rate of glyphosate for the control of wild oats from different wild oat populations, after different germination processes and at different temperatures. Studies on the influence of three wild oat populations and two germination processes on glyphosate efficacy were carried out in Chapter 3. Screening of nine wild oat populations to observe the level of sensitivity to glyphosate was done in Chapter 4. Influence of temperature on glyphosate efficacy in six wild oat populations was investigated in Chapter 5. A study to establish if changes in temperature during the duration of the experiment influence the efficacy of glyphosate on wild oat plants was carried out in Chapter 6. A summary of and recommendations about the entire study are given in Chapter 7. In chapter 3 wild oat populations from Malmesbury, Prieska and Eendekuil were germinated after treatment with ammonia gas, gibberellic acid and water and the germination rate and –percentage were calculated. Glyphosate (360 g a.e. L-1 formulation) at dosage rates of 0, 270, 540 and 1080 g a.e ha-1 were applied on the resulting wild oat populations treated with gibberellic acid and pure water that was growing in a glasshouse set at 20/25 °C night/day temperature. The germination test proved that ammonia and gibberellic acid treatments improved germination of the Malmesbury and Prieska populations compared to the water treatment. Gibberellic acid treatments had no influence on the survival of wild oat seedlings treated with glyphosate. Almost 100% control of the three wild oat populations was accomplished with 270 g a.e. ha-1 of glyphosate indicating that there were no glyphosate resistant plants present in the samples tested. The results also proved that gibberellic acid can be used as a treatment to enhance germination of dormant wild oat seeds without influencing the efficacy of glyphosate. In the first experiment of Chapter 4 wild oat populations from Lindley, Bethlehem A, Bethlehem B, Clarens, Prieska, Eendekuil A and B were germinated with gibberellic acid (1Mm GA3) and the resulting seedlings treated with 0, 270, 540 and 1080 g a.e ha-1 glyphosate dosage rates. Glasshouses were set at 20/25 °C night/day temperatures. Results of this study indicated that populations which were tested, showed no signs of resistance to glyphosate. The Prieska wild oat population showed some tolerance to glyphosate only at the 270 g a.e ha-1 dosage rate. All populations showed high sensitivity to glyphosate at the recommended 540 g a.e ha-1 dosage rate. In the second experiment in Chapter 4 two wild oat populations from Malmesbury and Eendekuil C that previously showed signs of possible resistance were germinated with gibberellic acid (1Mm GA3) and treated with 0, 270, 540 and 1080 g a.e ha-1 glyphosate dosage rates. Glasshouses were set at 20/25 °C night/day temperatures. Results of this study indicated that the Malmesbury and Eendekuil C populations showed no resistance to glyphosate. In Chapter 5 wild oat populations from Prieska, Bethlehem A, Malmesbury, Eendekuil A, B and C were germinated with gibberellic acid (1Mm GA3) and exposed to 0, 180, 360, 540 and 720 g a.e ha-1 glyphosate dosage rates. Plants were grown at four different temperature levels: 10/15 ºC, 15/20 ºC, 20/25 ºC and 25/30 ºC. Significant three-way interactions (p<0.05) between population, glyphosate dosage rates and temperature was noted in terms of the survival percentage, fresh plant mass pot-1 and dry plant mass pot-1. The Bethlehem A and Prieska populations had the highest survival rate percentage when glyphosate at 180 g a.e ha-1 was applied, this was revealed under glasshouse temperatures of 20/25 ºC (Bethlehem A), 15/20 ºC (Prieska) and 25/30 ºC (Prieska). The lowest survival rate percentage appeared when all the population were sprayed with 360, 540 and 720 g a.e ha-1 under all four temperatures in each glasshouse. These wild oat populations did not show resistance characteristics based on the results found. In Chapter 6 wild oat populations from Bethlehem A and Malmesbury were germinated with gibberellic acid (1Mm GA3) and exposed to 0, 180, 360, 540 g a.e. ha-1 glyphosate dosage rates. The plants were grown at two different temperature regimes 15/20 ºC and 25/30 ºC. Then half of the plants grown in each glasshouse were switched from 15/20 ºC to 25/30 ºC and vice versa on the day that glyphosate was applied. Significant three-way interactions between populations, dosage rate and temperature regime occurred when the temperatures were changed. The Bethlehem A population showed the highest survival percentage of 50% when switched from 15/20 ºC to 25/30 ºC temperature at 180 g a.e. ha-1 dosage rate. Malmesbury in contrast showed the highest survival percentage of 46% when switched from 25/30 ºC to 15/20 ºC at 180 g a.e. ha-1 dosage rate. Low survival percentages occurred at dosage rates of 360 g a.e. ha-1 and no plants survived at 540 g a.e. ha -1 dosage rates. The wild oat populations therefore did not show any sign of glyphosate resistance based on the results found.