273 Reduction of Fruit Cracking by Automatic Application of Calcium Chloride

Abstract

We have developed a system of automated intermittent salt application above the tree during a rain event that has shown very encouraging results (Washington State Hort Soc. Proc. 1995, Good Fruit Grower, vol. 47; pp. 23-24; Acta Hort. vol. 468 pp. 649 & 683) in Michigan and the Pacific Northwest. In 1998, we significantly reduced rain cracking with the system used in previous years. At the Southwest Michigan Research and Extension Center (SWMREC), on `Ulster', the control averaged 18% while the 0.5% calcium chloride had 6.7% cracks. Similar results were found for `Ulster', `Somerset', and `Rainer' at the Northwest Station. Cracking was greater in the upper part of the tree than the lower part for the control. The calcium chloride had less cracking on the upper part than the lower part indicating that calcium chloride applied from above the tree was not uniformly distributed to the lower part of the canopy in high enough concentrations. Multiple emitters per tree decreased this problem. We determined that there was an interaction with temperature. More fruit cracked at high temperature than low temperature. In the field more fruit cracked during the day than at night. We attribute this to the difference in day and night temperature. Using a bioassay system we able to determine the critical concentration of salt that must be on the fruit to inhibit water uptake and rain splitting up to a 4-h period. It ranged between 0.05% to 0.10 % depending on the variety and stage of development.