Impacts of using polyethylene sleeves and wavelength selective mulch in vineyards. II. Effects on growth, leaf gas exchange, yield components and fruit quality of Vitis vinifera cv. Merlot

Response of Merlot vines to wavelength-selective polyethylene mulch in the planted row and clear polyethylene enclosures (sleeves) around canes or cordons for 7 wk in the spring was studied in three Okanagan Valley vineyards. The mulch had no detectable effects on vine development, yield components and fruit quality. The sleeves advanced budbreak by 3 to 6 d, depending on the vineyard site, and increased the early growth rate of shoots. Time of budbreak and shoot growth rate were better predicted by cumulative daily mean temperature than by cumulative degree days (base 10°C). On the day sleeves were removed or opened at top, photosynthesis rates were higher in open-top sleeves than under ambient conditions due to higher mesophyll and stomatal conductances. Sleeves advanced the date of 50% bloom in all vineyards by approximately 10 d. Time of bloom, onset of veraison and the rate of fruit maturation were predictable from degree day accumulation. Sleeves advanced fruit maturation by 7 to 26 d, depending on the site, and reduced juice titratable acidity relative to °Brix at the coolest site. Sleeve effects on yield and yield components were inconsistent among sites. Sleeves reduced yield at one site due to lower cluster weights and apparently fewer berries per cluster. At another site, higher berry weights compensated for the apparent reduction in the number of berries per cluster in response to sleeves, and there was no effect on yield. At the third site, berry weights were lower in response to sleeves, likely in compensation for a higher number of berries per cluster. At one site where vines were shoot-thinned to retain primary shoots in the following year, the number of clusters per vine was unaffected by the treatments indicating that the treatments had no effect on bud fruitfulness. Key words: Wine grapes, photosynthesis, stomatal conductance, mesophyll conductance, plasticulture