Can Shade Help Trees Fight Citrus Greening?
At UF/IFAS, we are working on finding solutions for Florida’s citrus growers. This is a summary of one project made possible by state legislative funding for the UF/IFAS Citrus Initiative during the 2018-19 cycle. It documents how we are making progress and providing Florida growers with reasonable, pragmatic solutions to successfully grow citrus in the new age of citrus greening.
Researchers: Christopher Vincent, Horticultural Sciences; Yu Wang, Food Science and Human Nutrition; and Nabil Killiny, Plant Pathology
IMPACT: Providing shade for HLB-affected citrus trees may result in reduction of HLB symptoms, improved water uptake, improved photochemical performance and possible reduced attraction of the Asian Citrus Psyllid, extending the trees’ productive lives.
Like all photosynthetic plants, citrus trees need light to produce food. But in Florida, groves located in full sun sometimes receive more light energy than they can utilize. When this happens, photosynthesis slows down and the plants invest their energy in protecting their leaves from sun damage. Consequently, the trees have less food available for fruit production.
In groves affected by citrus greening disease, this situation is especially serious. The disease interferes with transport of carbohydrates from citrus leaves to other parts of the tree, making it less likely the tree will benefit from the carbohydrates it do s manage to produce. Reports suggest that citrus trees under shaded conditions are more tolerant of greening disease, so UF/IFAS Citrus Research and Education
Center tree physiologist Christopher Vincent investigated whether there were differences in the health of HLB-positive citrus trees growing in full sun, versus partial shade.
They located naturally occurring stands of grapefruit trees that are periodically shaded, and collected data indicating that shade exposure promotes optimal photosynthesis, and that it greatly reduced citrus greening infections by reducing the number of disease-transmitting insects that arrived. In a second experiment, the team assessed the effects of shade n sweet orange trees that were previously established in full sun and were all HLB-affected. The team constructed shelters for treatments that provided 30%, 50%, or 70% shade, plus a control group receiving full sun. Results after one year indicate that trees receiving 30% and 50% shade were holding more water in their tissues at midday — an important indicator of tree health — compared with trees receiving full sun or 70% shade. In a two-year follow-up study, team members hope to determine the amount of shade needed to reduce symptoms in greening-affected trees, enabling them to explore shading of trees as a strategy for mitigating HLB symptoms. In the future, this might be accomplished by spraying clay materials
directly onto trees to provide the amount of shade needed to increase productivity of HLB-affected trees.