Effects of the leaf galling density of grape phylloxera on Sangiovese grape productions

Daktulosphaira vitifoliae Fitch, the grape phylloxera, has represented the main problem for Vitis vinifera since its introduction in Europe, at the end of the 19th century, until French scientists proposed to use native American Vitis spp. as rootstocks to control this pest. Grafted, resistant grapevines have solved the issue for decades, nevertheless, in the 80’s leaf galling infestations appeared in Italy becoming more common and serious recently. Up to now, few studies have been carried out on the effects of leaf galling generations on grapevine growth and production. Since severe grapevine leaf infestations were recorded in Tuscany, a study was conducted in two vineyards in the Siena province in order to evaluate possible effects on grape production. The phylloxera infestation was monitored by sampling Sangiovese vines (V. vinifera) in summer 2017. Infested plants were divided into 3 different groups according to the infestation level and compared to uninfested vines. Grapes were sampled and addressed to technological and phenolic analyses. Although the weather has been very dry for the entire experiment, it has been possible to evidence a remarkable effect of the leaf infestation on grape quality. The phylloxera leaf galling incidence decreased as the temperatures increased. The photosynthetic rate and gas exchange decreased as the infestation level increased. Technological and phenolic analyses carried out on grapes highlighted a reduction of the grape quality. As a matter of fact, grapes from heavy infested vines showed reduced sugar and polyphenolic contents. These preliminary findings confirm the necessity to carry on further researches aimed at investigating the phylloxera population dynamics in order to define appropriate economic thresholds for applying control methods against this pest.