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Abstract
The response of ‘Red Delicious’ apples to low volume overtree evaporative cooling (EC) irrigation was studied over a 4-year period from 1969-72. While the amount of thermal load and irrigation system run-time varied from year to year, EC consistently resulted in fruit temperature reductions averaging 5.6°C (10.1°F) for the entire 509 hr the system operated over the 4-year period. In each of the 4 years, EC improved fruit quality; on the average increasing total reddish color 8%, solid red color 13%, soluble solids 1%, and fruit weight 22-g while reducing corking 8% and bitter pit 7%. The additional fruit coloration stimulated by EC concentrated harvest in the earlier portion of the harvest season. During the 4 years of the experiment, an additional 1/3 of the cooled crop was harvested, with sufficient solid red color to meet “extra fancy” U.S. grade, during the 1st 2 weeks of the seasons. Because of higher early-season prices, the concentrated earlier harvest of EC fruit is of considerable economic benefit. In locations where heat stresses are common, the use of EC and soil irrigation should be economically feasible.