Shade netting on subtropical fruit: Effect on environmental conditions, tree physiology and fruit quality

Extreme weather and climate events, such as very high temperatures, wind velocity and hail incidences that occur due to climate change and global warming, have detrimental effects on subtropical fruit orchards. Shade netting is one of the emerging techniques used by growers to protect their orchards against various biotic and abiotic stresses, such as excessive solar radiation, insects, hail as well as wind. There are different shade netting systems used in the fruit industry, these include insect proof screens, anti-hail and photoselective nets. This review presents the studies assessing the influence of shade netting on orchard microclimatic conditions, tree physiological parameters and fruit quality. Environmental conditions, such as air and canopy temperature, light intensity and wind speed, are notably reduced by shade netting, while relative humidity is significantly increased. Depending on the shade net type, colour and shading intensity, relative humidity is increased by 3.2-12.9%; light intensity, canopy temperature and wind velocity is decreased by 9-46%, 1.3-7.6% and 2.5-17.1%, respectively. Low bee activity and pollination services in trees grown under shade netting is a serious cause of concern. On tree physiology, shade netting enhances photosystem II efficiency, with high leaf numbers being common in subtropical trees grown under shade nets. Water use efficiency (WUE) is significantly improved under shade netting, and it reduces external fruit disorders, such as fruit splitting and sunburn. Although the influence of shade netting on phytochemical and nutritional attributes has been reported, there is little research on this area. Shade net colour and shading intensity have considerable effects on tree physiology and external fruit quality. It is crucial that each shade netting system is properly evaluated and analysed before being recommended for commercial use. The use of computational fluid dynamics for assessing, analyzing and improving the efficiency of shade netting systems in subtropical orchards should be explored.