Evaluation of transient, in-season applied heat to ‘Merlot’ and ‘Syrah’ wine grapes in Eastern Washington

Abstract

Sufficient heat accumulation is critical for fruit ripening in wine grape (Vitis vinifera). In 2013, a directed-heat application machine was evaluated for its ability to abridge vine phenology and improve fruit quality in commercially grown ‘Syrah’ and ‘Merlot’ in Paterson, WA. Heat was generated through the propane burning and applied to the vine via angled vents. The heat-generator was pulled by a tractor operating at 4 mph, resulting in a 2-second exposure of heat per vine. Rows were treated on a weekly to biweekly basis with transient heat treatments during: 1) bloom only, 2) véraison only, 3) both bloom and véraison, 4) from budbreak to harvest, and 5) a no-heat applied control. Data collected included the timing of phenological stages, percent fruit set, duration and level of heat exposure of the fruit and canopy, juice soluble solids, titratable acidity (TA) and pH at commercial maturity. Air temperature at the vent blower was ≈300 °F; however, by the time the air reached the canopy, air temperature was ≈130 to 150 °F. As a result, the typical increase in leaf or cluster temperature was 10 to 20 °F for 10 to 20 s. Heat application did not increase the number of berries per cluster or fruit set, did not enhance or abridge key vine phenological stages, did not increase soluble solids concentration accumulation, and did not alter juice TA or pH. Results indicate that heat application of this form does not advance vine phenology and in-field measured aspects of fruit quality in climates with large day-night temperature changes such as those in eastern Washington.