Postponing first shoot topping reduces grape cluster compactness and delays bunch rot epidemic
D. Molitor, N. Baron, T. Sauerwein, C. M. André, A. Kicherer, J. Döring, M. Stoll, M. Beyer, L. Hoffmann, and D. Evers
American Journal of Enology and Viticulture, vol. 66 no. 2, pp. 164-176, 2015
Field trials investigating the impact of the timing of first shoot topping in a vertical shoot positioning (VSP) trellis system on (i) the cluster morphology, (ii) the canopy structure in the cluster-zone, and (iii) the progress of the bunch rot disease severity, were conducted in the white Vitis vinifera L. cultivars Pinot gris and Riesling in Luxembourg in the years 2012 and 2013. First shoot topping was carried out at seven different time points between one week prior to flowering (BBCH 57) and four weeks after the end of flowering (BBCH 75–79) at approximately weekly intervals. Late first shoot topping reduced cluster compactness, delayed bunch rot epidemics and thereby prolonged the potential ripening period compared to the standard treatment (first shoot topping one week after the end of flowering). First shoot topping four weeks after the end of flowering delayed the moment when a disease severity level of 5% was reached up to eleven days. Total soluble solids increased by 0.77 to 2.24 Brix compared to the standard treatment, with no significant impact on grape yield. In conclusion, results show that postponing first shoot topping to the latest technically possible moment can be recommended to improve grape architecture and grape health as well as to optimize grape maturity and potential wine quality under cool climate conditions. Late first shoot topping could be implemented in bunch rot control strategies without causing any additional costs and might allow minimizing the use of pesticides.