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Poster: Biology & Disease Mgmt: Cultural Control


Fertigation and soil acidification sustain root density of huanglongbing-infected trees in Florida citrus groves
J. GRAHAM (1), E. Johnson (1), K. Gerberich (2), D. Bright (1) (1) University of Florida, U.S.A.; (2) University of Florida, Canada

Huanglongbing (HLB) is a devastating citrus disease caused by the phloem-limited bacterium Candidatus Liberibacter asiaticus (Las). Early symptoms of HLB include fibrous root loss and leaf blotchy mottle, followed by yield decline, leaf drop, and canopy dieback. As a consequence of initial bacterial infection of fibrous roots, a 30-50% reduction in fibrous root density and elevated soil Phytophthora populations were detected in field surveys. Continued sampling of Hamlin and Valencia orange trees on Swingle citrumelo rootstock in different stages of HLB decline revealed that root loss occurs in two stages. The second phase of root loss (70-80%) begins at the early stage of tree canopy thinning resulting from leaf drop and branch dieback. Managements have been implemented to reduce soil, nutrient and water stress, and Phytophthora root rot. They include frequent irrigation cycles, fertigation and acidification of irrigation water and soil to reduce rhizosphere pH, and fungicides. Root density of trees under these practices fluctuates seasonally and annually but has not declined over the last 3 years. Trees managed with soil acidification and fertigation have steadily recovered in health and yield.