Mitigation of Huanglongbing Effects on Grapefruit Trees Using Enhanced Nutritional Programs

The use of Enhanced Nutritional Programs (ENP) have been reported for ameliorate negative effects in health and productivity in citrus trees affected by the disease Huanglongbing (HLB). The present study evaluates the effect of different ENPs composed by five different sources of macro- and microelements. The treatments established are based on the combination of these fertilizers in order to evaluate the effect in the mitigation of HLB symptoms. The variables evaluated included the nutritional status, fruit drop, and yield in terms of fruit per tree, size and Gross Packing Value (GPV). After two years of treatment application, the fruit drop and the number of fruits per tree in trees sprayed with foliar fertilizers was not significantly different to the control (No ENP applied). However in terms of fruit size, the treatments that included applications of urea and potassium nitrate, produced significantly larger fruit than the control treatment. The increases in fruit size, represented a significant increment in GPV of approximately 66% to control trees., where the treatments with applications of potassium nitrate plus potassium phosphite, and DKP, potassium phosphite and microelements presented the higher values in this variable. Additionally, the same treatments showed increases in total fruit in comparison with control trees (38% and 31% more than control treatment respectively), and significant increments in large fruit production (8% more than control).