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R. Louis Baumhardt, W. N. Lipe, David Rayburn, and C. W. Wendt

Mild temperatures during late winter have caused early budbreak in grapes which resulted in freeze injury and significant crop losses in 1980 and 1988. Evaporative cooling of grapevines with microsprinklers when the air temperature exceeded 10 °C (50 °F) used 100 liters/min/hectare of treated grapes (11 gallons/min/acre) and delayed budbreak for a period of 7 to 10 days. Methods of reducing the amount of water used while not reducing the cooling were evaluated. The average hourly difference between wet and dry bud temperatures, measured with thermocouples, were summed during the system operation time and compared as a function of air temperature, wind speed, global radiation, and relative humidity limits. Limiting the cooling system operation time as a function of air temperature, wind speed, or global radiation reduced cooling efficiency by approximately a one to one ratio. Limiting system operation to humidities less than 60% reduced the amount of water used by 33%, with only a 9% reduction in cooling efficiency. By changing the wetting interval employed in this research from 25 seconds every three minutes to 25 seconds every four minutes, total water conservation would increase to 50% with insignificant changes in cooling efficiencies. These system modifications would reduce water application requirements to 50 liters/min/hectare of grapes (5.5 gallons/minute/acre).

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William N. Lipe, R. Louis Baumhardt, C.W. Wendt, and David Rayburn

The major production risk for grapes on the Texas High Plains is freeze injury to buds and wood due to deacclimation brought about by warm periods in late winter. Delaying plant development by any means would reduce risk from injury. Reducing cumulative heat summation between rest and bloom has resulted in delayed bloom on peaches but internal rest is not expressed in grapes. An evaporative cooling system using microsprinklers was applied to a Cabernet Sauvignon vineyard during Jan.-April 1989. The system provided a 25 second wetting period at 3 minute intervals anytime air temperatures exceeded 10° C. Bud temperatures were monitored continuously with a data logger and correlated to cumulative budbreak and plant development. Significant bud cooling was achieved and by normal budbreak cooled buds lagged uncooled buds by 72% in degree days. A similar lag in budbreak was recorded early with some cooled buds breaking 3 weeks after most uncooled buds were open. Cooled plants continued to lag uncooled plants at bloom and even at harvest where oBrix and pH were lower and total acids higher from cooled plots.

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R. Louis Baumhardt, W. N. Lipe, David Rayburn, and C. W. Wendt

Mild temperatures during late winter have caused early budbreak in grapes which resulted in freeze injury and significant crop losses in 1980 and 1988. Evaporative cooling of grapevines with microsprinklers when the air temperature exceeded 10 °C (50 °F) used 100 liters/min/hectare of treated grapes (11 gallons/min/acre) and delayed budbreak for a period of 7 to 10 days. Methods of reducing the amount of water used while not reducing the cooling were evaluated. The average hourly difference between wet and dry bud temperatures, measured with thermocouples, were summed during the system operation time and compared as a function of air temperature, wind speed, global radiation, and relative humidity limits. Limiting the cooling system operation time as a function of air temperature, wind speed, or global radiation reduced cooling efficiency by approximately a one to one ratio. Limiting system operation to humidities less than 60% reduced the amount of water used by 33%, with only a 9% reduction in cooling efficiency. By changing the wetting interval employed in this research from 25 seconds every three minutes to 25 seconds every four minutes, total water conservation would increase to 50% with insignificant changes in cooling efficiencies. These system modifications would reduce water application requirements to 50 liters/min/hectare of grapes (5.5 gallons/minute/acre).