The effect of five rootstock cultivars and two pruning methods with two crop loads each on Botrytis cinerea Pers. rot of Vi tis vinifera L. cv. Chenin blanc was investigated. The effect of these factors on bunch compactness, berry skin strength, pedicel strength, total soluble solids and nitrogen content of berries was also investigated to determine the correlation between these parameters and botrytis rot. The most rot occurred with Chenin blanc on Ramsey, 110 Richter and 101-14 Mgt when spur pruned, while the least rot occurred with Chenin blanc on 99 Richter when cane pruned.Rootstock cultivar had a significant effect on bunch compactness, berry skin strength, pedicel strength, cane mass and crop mass while rootstock cultivar and pruning method had a significant effect on total nitrogen and total soluble solids of berries. Except for bunch compactness none of the other parameters appear to have any direct effect on botrytis rot.Control of bunch rot of grapes caused by Botrytis cinerea Pers. is achieved mainly by chemical means. This is an expensive operation; the total cost in South Africa for wine and table grapes is estimated at R2,0 million per season. As a result of the rise in cost of chemical control as well as the fact that strains of B. cinerea resistant to some of the fungicides have occurred, it is unlikely that practical control of botrytis bunch rot can be achieved by the use of fungicides alone.It is known that many cultivation practices which are likely to increase vine vigour, e.g. excessive nitrogen fertilisation, vigorous rootstocks and irrigation, will increase the susceptibility of grapes to B. cinerea (Branas, 1960;Champagnol, 1969;Delas, 1972;Dry & Smart, 1982). Christensen (1981) found that by increasing the number of nodes per vine from 40 to 60 in the case of Chenin blanc, a significant decrease in botrytis bunch rot occurred. Practical experience in European viticultural areas has shown that choice of rootstock and scion cultivar as well as fertiliser application level, are very important factors with regard to control of botrytis bunch rot (Dry & Smart, 1982).The present study was carried out to determine the effect of certain cultivation practices, viz. the use of certain rootstock cultivars, pruning method and crop load on the incidence of botrytis rot of Chenin blanc. The effect of these factors on bunch compactness, as well as pedicel strength, berry skin strength, nitrogen and sugar content of berries was also evaluated in order to determine if a relation exists between these parameters and botrytis bunch rot.
MATERIALS AND METHODSA fourteen-year-old vineyard at Robertson, consisting of five rootstock cul ti vars viz. Ramsey, 99 Richter, 110 Richter, 101-14 Mgt and Jacquez with Chenin blanc as scion, was used in this study. Vines were trellised ac'cording to the Perold system as described by Zeeman (1981).A randomized block design in which each rootstock cultivar was replicated four times was used. Each plot consisted of four rows with seven vines per row. Two pruning methods v...
