|Bergamin Filho, Armando|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2012
Publication Date: N/A
Citation: N/A Interpretive Summary: Huanglongbing (HLB) is the most destructive disease of citrus known. It threatens the viability of citrus industries worldwide, including those within the United States. The disease is caused by bacteria and spread by a small insect vector known as a psyllid. Disease control is predicated on the use of insecticides to control the vector, and removal of infected trees which act as sources for the disease. However, even these control methods have been inadequate to completely the manage the disease. Recent work in Brazil has demonstrated that the disease is most effectively controlled with an areawide approach. That is growers must get together and manage entire regions by the use of insecticide suppress psyllid populations. If all of the vectors are suppressed within the region, the disease does not spread. This paper demonstrates the effect of such an areawide management strategy for HLB. It shows the difference between regional management and incomplete regional management. Such management controls the insect populations to such a level that the progress of the disease is considerably slowed. This management strategy has become the predominant intermediate strategy recommended to growers both in South and North America.
Technical Abstract: Huanglongbing (HLB), caused by Candidatus Liberibacter spp. and transmitted by the Asian citrus psyllid Diaphorina citri (ACP), is an important threat to citrus industries worldwide, causing significant yield loss. The current recommended strategies to manage HLB are to: (i) eliminate HLB symptomatic trees to reduce sources of bacterial inoculum, and (ii) apply insecticides to reduce psyllid vector populations. The objective of this study was to assess the effectiveness and the importance of both strategies applied within young citrus plots (Local management), in different frequencies and combinations, on HLB temporal progress. Two factorial field experiments, E1 and E2, were initiated in a new plantation of sweet orange in a HLB epidemic region of Sao Paulo, Brazil, in October/05 and May/06, respectively. Local inoculum reduction levels for E1 were every 4, 8 and 16 weeks, and for E2, every 2, 4, 12, and 26 weeks. Local vector control levels for E1 were no control, program A (PA) and program B (PB), and for E2, no control and program C (PC), as follows. Psyllid control was done with two 56-day-interval soil or drench applications of systemic insecticides concurrently with the rainy season each year; and during the rest of the year, with insecticide sprays every 28 days for PA, and every 14 days for PB and PC. Regional HLB management was present for E1 and absent for E2. The beginning of the HLB epidemic was delayed for 10 months in E1, but wasn’t affected by different local strategies for both experiments. After 60 (E1) and 53 (E2) months, the HLB incidence and progress rates were not affected by different frequencies of local inoculum reduction in either experiment, and were different only in plots with and without local vector control in E2. In E1 the disease incidence was reduced by 90% and the disease progress rate by 50% in both plots with and without vector control. These reductions were explained by smaller psyllid populations and lower frequency of bacterialiferous psyllids in E1 compared to E2. Annual productivity remained increasing over time in E1 as expected for young plantings, whereas remained stable or decreased in E2. These results confirmed the great importance of primary infection by migrating bacterialiferous ACP populations on HLB epidemics and suggest that an area-wide inoculum and ACP management heavily affects HLB control.