Comparison of Commercial Sunburn Protection Products

Sunburn is the primary physiological cause of apple cullage in Washington, sometimes damaging up to 50% of the fruit in a given orchard. Losses occur both as surface damage as well as predisposition to storage disorders. Trials were carried out from 2005 to 2008 to evaluate and compare the efficacy of commercially available sunburn protectants and to evaluate their ease of cleanup on a packing line. Materials tested included: Cocoon, Eclipse, Fruit Shield, Invelop, Raynox, Raynox Plus, Sun Guard, and Surround WP.  All materials were applied four times throughout the season starting in early July; applications were made consistent with product labels for concentration and use of adjuvants.  At harvest, individual fruit was graded for sunburn according to the Schrader/McFerson system (0 = clean, 6 = necrosis). All materials tested increased the percentage of sunburn-free fruit, enabling packers to move more fruit into the highest grade and increasing the returns for individual growers.  We evaluated standard warehouse washing and rinsing of fruit on a research packing line, since residues of protectants can cause marketing problems. Visible residues were observed before placing fruit on the line and after 24 hours of drying time. All materials cleaned easily off fruit flanks. Residues remained in the stem bowls at significantly higher levels for kaolin clay and calcium carbonate-based products, which would be commercially acceptable in most cases.