Budburst delay and berry ripening after vegetal oil application in Austria

Abstract

Context and purpose of the study – Occurrence of freezing temperatures in early spring when grapevine shoots are developing is termed late frost in viticulture. Young green tissues are very sensible to temperatures below zero and damages often lead to important yield and quality losses such as the case in Europe in 2017. An indirect method to avoid late frost damage in vineyards consist in delaying the budburst. Previous research reported similar effects by applying vegetal oil on dormant buds. Here, we tested the application of rapeseed vegetal oil during late winter to delay the budburst on two V.vinifera cultivars of interest in Austria, Grüner Veltliner (GV) and Zweigelt (ZW).

Material and methods – The experiment was carried out in 2017 and 2018 in an experimental vineyard located in Krems (N-E Austria), on 4 consecutive rows of ZW planted in 2004 and 4 consecutive rows of GV planted in 2007 and pruned as single Guyot. Experimental design consisted on 8 blocks of 12 vines each (4 controls and 4 oil-treated) per cultivar. Rapeseed oil (10% v/v in water) was manually sprayed on dormant buds in March (ca. 30-45 days before budbreak). The budbreak phenology and shoot development was assessed at the beginning of the growing season and berry samples were collected 5 times during ripening to determine possible impact of the treatment. At harvest, yield and leaf area was determined.

Results – The oil application resulted in a delayed budbreak for both cultivars and in both seasons. While in the first season oil-treatment did not impact yield or berry composition in both cultivars, during the second season phytotoxicity (bud necrosis or reduced shoot growth) was observed mainly in Zweigelt, leading to reduced yields and the alteration of some berry compositional parameters. G. Veltliner showed a lower degree of phytotoxicity (mainly reduced shoot vigor) that eventually disappeared during the season, resulting in no statistical differences in berry composition or yields compared with the non-treated controls. Overall, our results suggest an interaction between genotype, climatic factors (mainly temperature) and oil application, resulting in variable effects observed after oil application that needs to be fully characterized to avoid possible phytotoxic effects and fine tuning the technique.