Effects of mechanical leafing and deficit irrigation on Cabernet Sauvignon grown in warm climate of California

Abstract

Context and purpose of the study – San Joaquin Valley accounts for 40% of wine grape acreage and produces 70% of wine grape in California. Fruit quality is one of most important factors which impact the economical sustainability of farming wine grapes in this region. Due to the recent drought and expected labor cost increase, the wine industry is thrilled to understand how to improve fruit quality while maintaining the yield with less water and labor input. The present study aims to study the interactive effects of mechanical leafing and deficit irrigation on yield and berry compositions of Cabernet Sauvignon grown in warm climate of California.

Materials and methods – Field grown spur-pruned Cabernet Sauvignon vines grafted on Freedom rootstocks trained on quadrilateral cordons were included in this study. Two (water deficit) × three (mechanical leafing) factorial trial with a split block design, replicated in 5 times, was applied in 2018. Ten rows of vines (200 vines per row) were divided into two groups and each group was assigned to one of water deficit treatments as the “main plot”. Three mechanical leafing treatments were allocated randomly in the “main plot” as the “sub plot”. Two levels of water deficits included: 1) “sustained deficit irrigation” with 80% ETc from fruitset to harvest; 2) “regulated deficit irrigation” with 50% ETc from fruitset to veraison and 80% ETc from veraison to harvest. Three mechanical leafing treatments using the cut-suck type mechanical leafer to remove basal leaves on the “morning” side of the canopy included: 1) bloom leafing (stage EL-21); 2) pea size leafing (stage EL-31); 3) no leafing. Six vines in each “sub plot” were labeled as data vines.

Results – Leafing at bloom and pea size reduced about 8% of total leaf area as the comparison of control, however, bloom leafing only resulted in the temporary improved fruit-zone light exposure, while water deficit treatment did not cause any significant difference on leaf area. Water deficit had a bigger impact on yield than leafing with 20% yield reduction resulted from severe water deficit, and no impact on yield was found from leafing. The yield reduction was mainly driven by reduced cluster weight associated with the smaller berry size. Similar result was also found for leaf area/fruit ratio, while all the ratios fell in the previously published optimal range.As for berry composition, water deficit reduced titratable acidity and 3-isobutyl-2-methoxypyrazine (IBMP) while improving berry anthocyanins. Bloom leafing improved berry anthocyanins and increased IBMP. Resulted wine color was also improved by water deficit and bloom leafing. Key words: Mechanical leafing, Water deficit, Yield, Fruit quality, Wine chemistry