Browsing by Author "Ntombela, Bongani Nkosinathi"
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- ItemOptimizing the use of pre-emergent herbicides in wheat production, under conservation agriculture practices in the South-Western Cape Region(Stellenbosch : Stellenbosch University, 2019-04) Ntombela, Bongani Nkosinathi; Pieterse, P. J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Agronomy.ENGLISH ABSTRACT: The interception of herbicide by residue cover can result into poor weed management, leads to more weed seeds reaching the soil seed bank, which results in higher weed pressure in the following seasons and, in the long-term, these sub-lethal doses can lead to the development of non-target site herbicide resistance. Therefore, the aim of this study was to investigate possible dosage rate/application rate combinations that can result in the required amount of selected pre-emergent herbicides to reach the soil surface at different levels of residue cover. The efficacy of pyroxasulfone herbicide when applied on increased amounts of residue cover was executed in a field trial, discussed in Chapter 3 and a glasshouse trial, discussed in Chapter 4. For field trials at Langgewens residue cover were arranged to 0, 6 and 12 t ha-1 and to 0, 4.5 and 9 t ha-1 at Tygerhoek. Pyroxasulfone’s treatment were as follows; recommended and 1.5 times the recommended dosage rates and recommended and double the recommended application rates. Weed and crop counts were made at seven weeks after planting and at crop anthesis. Vegetative growth parameters were determined at anthesis. Yield components were determined just before harvesting. After harvesting; yield, thousand kernel mass and hectolitre mass were determined. For the glasshouse trial, 50 commercial ryegrass seeds and five wheat seeds were planted per pot. Wheat residue cover was arranged as 0, 1.5, 3, 4.5 and 6 t ha-1. Pyroxasulfone was applied at similar dosage rates and application rates as in Chapter 3. After the herbicide was applied, 5 mm of clean water was used to wash off the herbicide. Ryegrass counts was made at 7 weeks after planting (WAP). After harvesting; vegetative growth parameters and yield were determined. Doubling of recommended application rate had a little impact compared to increasing the dosage rate. A field trial comparing the effectiveness of weed control of pyroxasulfone, prosulfocarb plus triasulfuron and triallate when applied on increased amounts of residue cover is discussed in Chapter 5. The study was executed at Tygerhoek and Langgewens with residue cover arranged to result in 0, 5.5 and 11 t ha-1 and 0, 4.8 and 9.6 t ha-1 respectively. At both sites, herbicide dosage rates and application rates were arranged as in Chapter 3. Data was collected as in Chapter 3. Pyroxasulfone at increased dosage rates, controlled weeds better than other herbicides followed by prosulfocarb plus triasulfuron. Triallate treatment performed poorly across residue cover levels, even on an increased dosage rate. The results showed similar trends to the previous two chapters indicating that an increase in dosage rate was more effective than an increase in application rate to improve the efficacy of pre-emergence herbicides under high residue conditions.