2018 ASHS Annual Conference

The major apple growing regions in WA are located in the semi-arid eastern half of the state which experiences harsh environmental conditions due to the rain shadow effect from the Cascade mountain range. Fruit sunburn results in substantial losses to the apple industry every year. To mitigate these losses, the adoption of protective netting to reduce fruit sunburn and trees stress is increasing in WA. The types of protective netting structures commonly used by commercial apple growers in WA are exclusion netting, horizontal over the top of the orchard only and louvered / partial overhead netting. Factors that influence a grower’s decision on the netting structure include cost, amount of protection needed and tree row orientation. The primary benefits of protective netting is the reduction in solar radiation reaching the orchard environment underneath it. Protective netting primarily modifies light quantity and quality underneath by reducing light intensity by an approximately pre-determined percentage. Depending on the cultivar, apple growers in WA use protective netting that reduce the total amount of incoming solar radiation by 10–30% depending on the cultivar. This results in a reduction in photoinhibition and improved photosynthetic light use efficiency. In young orchards under protective netting, trees are able to fill-in the canopy earlier compared to an uncovered control. The reduction in incoming solar radiation under protective netting reduces the occurrence of sunburn by decreasing the amount of radiation reaching the fruit surface and reduces photooxidative damage to the fruit peel. Protective netting has been shown to consistently reduce the incidence of sunburn in apple under high light intensity growing conditions experienced in WA. Overall, protective netting provides is a resilient innovation to protect apple fruit from sunburn and reduce abiotic stress that limits tree establishment in WA.