Efficacy of Area-Wide Inoculum Reduction and Vector Control on Temporal Progress of Huanglongbing in Young Sweet Orange Plantings

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 eliminate HLB-symptomatic trees to reduce sources of bacterial inoculum and to 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 an HLB epidemic region of Sao Paulo, Brazil, in October 2005 and May 2006, respectively. Local inoculum reduction (tree removal) intervals for E1 were every 4, 8, and 16 weeks and, for E2, every 2, 4, 12, and 26 weeks. Local vector control strategies for E1 were no control, program A (PA), and program B (PB); and, for E2, no control and program C (PC), as follows. Psyllids were controlled 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 compared with appearance of the first diseased tree in E2 but wasn't affected by different local strategies in either experiment. 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 plots both with and without vector control. These reductions were explained by smaller psyllid populations and lower frequency of bacterialiferous psyllids in E1 compared with E2. Annual productivity increased over time in E1, as expected for young plantings, but remained stable or decreased in E2. These results confirm that immigration of bacterialiferous ACP vectors plays a critical role in HLB epidemics and suggest that area-wide inoculum reduction and ACP management strongly affect HLB control.

Asymptomatic spread of huanglongbing and implications for disease control

“…If it is feasible to attain a 90% psyllid population reduction compared with the population without psyllid control, groves could be producing fruit free of HLB for 2+ y beyond the time of symptom onset in uncontrolled groves. Such reductions from spraying adult psyllids have been demonstrated in Brazil, for example (28). The question of how to reach 90% reductions in psyllid populations relative to uncontrolled conditions in a multigrove setting is starting to get serious consideration from grower cooperatives (www.crec.ifas.ufl.edu/extension/chmas/chma_overview.shtml).…”

Áreas de abundancia potencial en México del vector del Huanglongbing, Diaphorina citri (Hemiptera: Liviidae)

“…En el estado actual del modelo, es innegable su contribución potencial a la planeación para realizar el manejo regional que se ha planteado para solucionar el problema (Bassanezi et al, 2013;SENASICA, 2014 On the presence of the disease in Chiapas, the fact remains that it lacks a clear pattern of the epidemic associated with the natural flow of the vector potential, since the municipalities concerned are distant (SENASICA, 2014); is likely to anthropocentric components were related to the occurrence of the disease in the affected areas. These factors are not yet included in the model, since it is difficult to distinguish a trends that could influence become valid data for the system because they can generally occur in accidental, circumstantial or occur in a very disjointed ways, and are indeed difficult to compare such with the information analyzed Gottwald et al (2013) to detect the disease in urban areas in the United States.…”

“…In the current state of the model, its potential is undeniable contribution to planning for regional management that has come to solve the problem (Bassanezi et al, 2013;SENASICA, 2014).…”

Phenology of Asian Citrus Psyllid (Hemiptera: Liviidae) and Associated Parasitoids on Two Species ofCitrus, Kinnow Mandarin and Sweet Orange, in Punjab Pakistan

“…Vector reduction is a signiÞcant factor in HLB management because transmission rates of bacteria increase with an increasing number of CLas-infected psyllids feeding on a plant and the likelihood of disease development subsequently increases (Pelz-Stelinski et al 2010). Consequently, reduced psyllid population densities can lead to a decrease in the incidence of HLB (Etienne et al 2001) because fewer bacteriacarrying psyllids capable of inoculation are feeding on trees (Bassanezi et al 2013).…”