Retractable Netting and Evaporative Cooling for Sunburn Control and Increasing Red Color for ‘Honeycrisp’ Apple

Abstract

Protective netting and evaporative cooling are commonly used for sunburn protection in apple (Malus domestica Borkh.) orchards in semiarid environments such as central Washington state. Sunburn is caused by a combination of solar radiation and heat, which can cause significant economic losses. Although protective netting and evaporative cooling can be effective for preventing apple sunburn, netting can also introduce new risks, including red color development on the fruit surface. This study evaluated whether retracting netting before harvest improves red color development and/or changes sunburn risk compared with leaving netting in place until after harvest. An experiment was conducted that compared three netting treatments: 1) netting from June until harvest, 2) netting retracted 10 d before harvest, and 3) no netting all season combined with the presence or absence of evaporative cooling. Fruit was harvested and assessed for sunburn incidence and external quality characteristics immediately after harvest. In retracted netting treatments, red color was higher when netting was retracted compared with the nonretracted controls, and sunburn risk did not increase with netting retraction. Evaporative cooling reduced sunburn incidence. Retractable netting can be used to minimize the loss of fruit to sunburn while allowing a full light environment that promotes red color near harvest. There is no inherent increase in sunburn risk from netting retraction, and the proportion of fruit with red color improved.

Keywords

• fruit quality
• heat stress
• protective cropping
• malus domestica