Since Huanglongbing (HLB) was first found in Florida, growers have recognized the importance of controlling the Asian citrus psyllid (ACP) that vectors the disease.   ACP management programs have been developed and applied over large acreages, yet in many instances, the incidence of the disease continues to increase.   When asked, the growers invariably report that they are controlling ACP and it is obvious that the control programs are reducing the level of ACP in the groves.  However there is an outstanding question as to whether the levels of ACP are being reduced enough to limit the spread of HLB.  In most cases, growers have not implemented ACP scouting programs so the level of infestation is based on rough grove surveys and feelings.  Even if scouting programs are in place, there are no established data-based thresholds to trigger additional applications of pesticides resulting in a “chasing” approach where applications are made after an infestation is found.  Southern Gardens has had an ACP and HLB scouting program in place for many years.  By comparing the annual ACP levels to resulting HLB infection succeeding years, it may be possible to elucidate thresholds and then design ACP control programs that effectively limit the spread of HLB.  Data will be presented for three years of ACP scouting and four years of HLB scouting in an attempt to show the level of control that must be achieved in order to limit the spread of HLB.  The bottom line is that control thresholds are very low and the level of ACP control that must be achieved in order to limit spread HLB is much lower than most growers realize.

Florida growers have reported that enhanced nutritional programs (ENPs) maintain productivity of HLB-infected trees.  However, efficacy and sustainability of the nutritional approach for HLB disease management remains uncertain.  Complementary studies of multiple ENPs and their individual components compared to the standard nutritional program (SNP) on nursery and field trees were initiated in 2010.  Two independent nursery trials were initiated with final data collection of the second trial currently underway.  The field site was chosen for its mix of healthy, presymptomatic, and HLB symptomatic trees to determine if observed differences resulted from effects on healthy or infected trees.  We have found no evidence of reduced phloem plugging in ENP treated nursery trees.  Candidatus Liberibacter asiaticus (Las) populations are similar for ENPs and the SNP.  Minor differences in Las movement have been observed.  Las invaded new flush tissue faster in ENP treated trees than SNP trees.  Phosphite treatments have caused Las to favor early invasion of root tissue compared to other treatments.  Preliminary observations of the second nursery trial suggest that foliar symptoms are more apparent on the standard nutrient program compared to ENPs; however, root and canopy decline are unaffected.  Fruit yield and HLB symptoms in field trees treated with ENPs have not differed significantly from the standard nutritional program after two years.  Third year yield data will be presented.