By Christopher Vincent, Yu Wang and Nabil Killiny
Mild shade reduces stress, increases growth and yield, and may improve pest management under huanglongbing (HLB). It reduces high temperature and water stresses. Shade also may reduce HLB transmission by making trees less visible to Asian citrus psyllids (ACP). Shaded trees have less ACP, and shade appears to reduce the severity of HLB symptoms in already infected trees.
Over a 3-year University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) study, 30% shade doubled the yield, on average, of HLB-affected shaded trees compared with trees in full sun. This suggests a sustained increase in both growth and yield, which continued during more and less challenging weather events. Too much shade, though, (50% and 70% shade) reduced yields relative to the 30% level.
Shade reduced many symptoms of HLB in infected trees in the field. Shade improved water status and enhanced photosynthesis in HLB-positive trees. It also made trees more heat tolerant. This may be because the combination of high light and HLB pushes trees beyond their capacity to acclimate. Overall, shaded trees were less stressed and grew more than full-sun trees.
Shade can be utilized in three ways:
1) Citrus under protective screen is already being used.
2) Individual protective covers can be optimized to provide the healthiest amount of shade.
3) Particle film technology (kaolin clay) can be similarly dosed.
It may be worthwhile to invest in approaches to shade netting for production of high-value varieties.
Acknowledgment: Funding for this project was from the UF/IFAS Citrus Initiative funded by the Florida Legislature.
Christopher Vincent (civince@ufl.edu), Yu Wang and Nabil Killiny are associate professors at the UF/IFAS Citrus Research and Education Center in Lake Alfred.
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