Protective Rain Covers Influence the Rain-inducing Cracking and Quality of Sweet Cherries

Abstract

For many years, researchers and growers have attempted to find methods to alleviate the rain-induced cracking of sweet cherries. Cracking is thought to be caused primarily by the osmotic uptake of rain water through the fruit skin. A 3-year study was conducted at East Malling to test the hypotheses that rain covers reduce, while irrigation increases, fruit cracking. Two types of rain shelters, with and without trickle irrigation, were compared against control treatments on 8-year-old `Merchant'/Colt trees. Covers reduced cracked fruit by up to 11% in 1991, 7% in 1992, and 25% in 1993 when natural cracking on uncovered trees was ≈20%, 25%, and 40%, respectively. Trickle irrigation was associated with a 6% increase in fruit cracking in all 3 years. Tree covers and irrigation also tended to increase fruit size and maturity. Fruits from beneath covers were lower in soluble solids concentration and were firmer in comparison with fruits from uncovered trees. This study indicates that tree covers, while affording some protection against rain-induced cracking, do not altogether prevent the problem. Furthermore, irrigation appears to aggravate cracking when used with tree covers. A mechanism for cracking under covers will be discussed in relation to rainfall, fruit transpiration, and tree water relations.