Browsing by Author "Joseph, Beverley-Anne"
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- ItemThe effect of timing of stripping on hop production under South African conditions(Stellenbosch : Stellenbosch University, 2015-12) Joseph, Beverley-Anne; Agenbag, G. A.; Reinten, E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Agronomy.ENGLISH ABSTRACT: Hops is a small, but important agricultural commodity in South Africa. The hop cones contain secondary metabolites responsible for the flavour, aroma and bitterness in beer. The George and Waboomskraal area are the best suited for growing hops due to climate and geographical location. The optimum latitude for hops growing is 45° - 54° north and south of the equator, while these areas are at 34° S. International hop varieties are not adapted to the South African climate. Winters are too warm and summer days too short, thus all the varieties grown in South Africa have been bred for these specific conditions. The Hop breeding and research program strives to develop internationally competitive varieties with higher yields, desirable brewing characteristics, reducing input costs and increased productivity. To evaluate the current agricultural practices and to determine whether some of these practices negatively affect the plant health and yield, a study was conducted to investigate the effect of the time of stripping. Stripping refers to the practice of removing basal growth of the lower laterals and untrained bines. The study was done in two different microclimates, namely George and Waboomskraal. The aim was to determine the effect of the time of stripping on the vegetative growth, light interception, biomass, soft resins (alpha and beta acids), yield, rootstock weights and carbohydrate concentrations. The effect of stripping was also evaluated on different planting systems and plant maturity, namely Tram lines and conventional planting and 3 years old versus 5 year old plants. The effect of early stripping in terms of dry weight on mature plants is considerably less than the effect on younger plants. Young plants delivered lower dry weights, but accumulated higher carbohydrate reserves in the early stripping treatment. On young plants early stripping showed a significant difference favouring yield on tramlines. There is a general trend across all sites of higher crop efficiencies in the early stripped treatments. Growers could significantly increase yields without negatively affecting the quality (alpha and beta acids) by applying early stripping, especially in the George area. The effect of early stripping becomes more apparent in consecutive years as the time of defoliation affects foliage, carbohydrate concentration, canopy microclimate and light interception resulting in increased yields, especially on tramlines. From this study it can be concluded that early stripping appeared to have an influence on the dry root weight, carbohydrate concentration, light interception, crop efficiencies, yield and biomass. This practice is not only environmentally friendly by using less herbicide, it also delivers an economic gain. The effect of the time of stripping in consecutive years and different varieties deserves further study.