Response of fruitset and other yield components to shoot topping and 2-chlorethyltrimethyl-ammonium chloride application

Background and Aims: We investigated the effectiveness of shoot topping and 2-chlorethyltrimethyl-ammonium chloride (CCC) application on the control of fruitset and other yield components on the grapevine varieties Cabernet Sauvignon, Chardonnay and Tempranillo at two sites over two or three seasons. Methods and Results: Treatments were applied before and during the flowering period. Fruitset and yield per vine increased in response to both shoot topping and CCC treatment, especially when shoot topping was applied between E-L stages 19 and 23, and when CCC was applied 1 week before flowering. All varieties at both locations responded to shoot topping to some degree: from 20 to 57% relative to the control for fruitset and from 16 to 97% for yield per vine. Conclusions: Fruitset, and, thus, yield, can be improved by cultural practices in all seasons, but the magnitude of the response may be greatest in those seasons when fruitset is lower than the average. Neither berry number per bunch nor the visual appearance of the bunches were reliable indicators of fruitset performance. Significance of the Study: Optimal timing of shoot topping and CCC application as cultural practices is critical to maximise the response. The 'Coulure Index' and the 'Millerandage Index', which are described for the first time, are novel and useful indicators of fruitset that have been developed to quantify the reproductive performance of grapevines.