|By using a supplementary leaf nutrient programme, specially developed by Agro-Hytec for wine grapes, a whole range of benefits can be obtained, including stretching of bunches, improvement of set, better resistance to heat and moisture stress, increased crop size, improved sugar content, more even ripening and improved wine quality.
According to Charl Viviers, technical consultant of Agro-Hytec, the basis of the leaf nutrient programme is the marine algae extract Symspray, which has a high cytoquinine content. It is the richest commercial agricultural source of cytoquinine available on the market (1% with a biotest). The functions of cytoquinine in the plant are wide-ranging and include the stimulation of cell division and the mobilisation of nutrients to growing organs, thus benefiting their development. A further important benefit is the maintenance of the integrity of the cell membranes which counter the effect of heat damage and delay ageing deterioration. Applied with the Symspray are nutrients aimed at supplementing deficits in specific stages of development.
The application of the Agro-Hytec nutrient programme stimulates flower bunch growth as opposed to shoot growth. This occurs because the apical dominance of the shoot tip vis – vis the flower bunch is reduced. The same applies to weaker shoots that bud later and are therefore subject to the primigenic dominance of the stronger shoots. By strengthening these weak shoots, better pruning canes are obtained for the next year.
Poor set as a result of heat stress may be improved by using Symspray at the onset of flowering. Sufficient quantities of Symspray make the leaf tissue greener by attracting nutrients and activating the cells. In wine grapes vine leaves showed 18% less moisture loss. During critical moisture shortages under dryland conditions or with little available irrigation water, the nutrient programme can therefore help to save moisture and keep the leaves functional for a longer period in order to produce sugars and other substances required for grape and wine quality.
Pure potassium, provided by the programme, is the most important nutritional element required in large quantities by grapes during ripening and at the time of harvesting, up to 60% of the potassium in the vine may be in the grapes. Potassium is particularly important for the production of sugar and phloem load. When there is a shortage in the vine, the bunches are first supplied and the leaves neglected. The leaves then begin to deteriorate prematurely and may even fall off. Potassium shortages occur especially on sandy soils that have little thereof to begin with, but dry conditions may cause insufficient potassium to be absorbed during ripening.
The effect of the Agro-Hytec leaf nutrient programme was tested in a statistically designed experiment in commercial vineyards in the Paarl and Somerset West vicinities. The grape cultivars included in the experiment were Cabernet Sauvignon, Pinotage, Cinsaut and Chardonnay. Grapes for small scale vinification were supplied to the Department of Viticulture and Oenology at the Stellenbosch University, where wines were made by Loftie Ellis. The bottled wines were organoleptically evaluated and chemically analysed. Wine samples were also sent to the ETS laboratory in California for analysis of the phenolic components. Statistical analyses of the data were done where applicable on all cultivars, and where colour was involved, on the red wines only.
The increase in the sugar content as a result of the treatment was highly significant (Fig 1), while the pH increased significantly with treatment (Fig 2). The treated grapes therefore ripened earlier. If the untreated grapes had been left to hang longer to develop sugar, the pH would have increased in any event. Here the most important effect on wine quality is the sugar:pH ratio and this improved significantly with the treatment (Fig 3).
The improved colour density in the wines (Fig 4) and the degree of red pigment colour (Fig 6) were significant for the experiment as a whole. For the individual vineyards, only the colour density of Cabernet Sauvignon (Fig 5) was significantly improved by the treatment. The improvement in the phenolic components, which was best in Cinsaut and Cabernet Sauvignon, is indicated in Figures 7 and 8. The components on the left side of the graph have the strongest bearing on wine quality. In the graphs the components in the wines of the untreated control are indicated as 100%, while the wines made from treated grapes are given values relative to that.
Loftie Ellis summarised the organoleptic tests as follows: “Wines prepared from treated grapes have shown higher extract levels, better colour and higher phenolic levels than the wines from untreated grapes. General comments made by the judges were that these wines exhibit more character and intensity of flavour on the palate than the corresponding control wines.”
For more information, contact Charl Viviers on 082 466 0662 .