Location: Subtropical Plant Pathology Research
Title: Orchard and nursery dynamics of the effect of interplanting citrus with guava for Huanglongbing, vector, and disease management Authors
Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 2014
Publication Date: July 5, 2014
Citation: Gottwald, T.R., Hall, D.G., Kriss, A.B., Salinas, E.J., Parker, P.E., Beattie, G.C., Nguyen, M.C. 2014. Orchard and nursery dynamics of the effect of interplanting citrus with guava for Huanglongbing, vector, and disease management. Crop Protection. 65:93-103. Interpretive Summary: In 2006 the authors became aware of an alternative control for citrus huanglongbing (HLB) reported by citrus farmers in the Mekong Delta of Vietnam. The authors visited citrus production areas in the Mekong Delta in 2007 and confirmed that citrus interplanted with guava appeared to be surviving for many years longer than when citrus is grown alone as a monoculture. Guava appeared to be releasing unique volatile chemicals that either inhibited or confused the vector of citrus HLB known as the Asian citrus psyllid (ACP). To test this in Western Citriculture, we establish replicated field and nursery plantings in Florida and in Texas of citrus interplanted with white guava and compared it with plantings where citrus is grown as a monoculture. Evaluation of the floor and Texas field plantings over the next two years indicated that there was no difference in disease incidence over time or insect vector populations between the citrus-guava interplanted and citrus monoculture field plantings. However there was a slight inhibition when citrus was interspersed with guava in nursery settings. Our conclusion is that interplanting citrus with guava as a management strategy for suppression of vectors and control of HLB was ineffective in field settings and although gave some suppression in citrus nurseries, was not an adequate control strategy there either.
Technical Abstract: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an important pest of citrus in the United States of America primarily because it vectors ‘Candidatus Liberibacter asiaticus’, the bacterium putatively responsible for Asiatic huanglongbing (HLB). Asiatic HLB is considered one of the most serious diseases of citrus. In the United States where Asiatic HLB was first found in the state of Florida, vector control is considered an essential component to mitigate pathogen infection and spread of the disease. Therefore commercial citrus growers in Florida have adopted intensive insecticide programs to manage psyllid populations. However, the repetitive use of insecticides for ACP control is expensive and interferes with biological control of ACP and other citrus pests. As an alternative to insecticides, reports from Vietnam indicated that infestations of ACP in citrus (and consequently incidence of HLB) were reduced when citrus was interplanted with white guava, Psidium guajava L. Speculations were that guava volatiles reduced ACP infestations in citrus by either repelling ACP or interfering with ACP ability to locate and infest citrus grown next to guava. We present the results of two studies conducted in Florida (where both ACP and HLB occur) to assess ACP infestations and HLB incidence in citrus interplanted with either white or pink guava compared to infestations and disease incidence in citrus grown as a monoculture, both in orchards and nurseries. In the field study, the effect of guava on ACP infestations was assessed alone and in combination with insecticide or oil applications. Significant reductions in ACP infestations in citrus interplanted with pink guava were identified, but there was no reduction in citrus interplanted with white guava. The effect of pink guava on ACP infestations could be investigated further. However, intercropping citrus with either white or pink guava did not prevent the introduction and spread of HLB. Conclusions from field studies regarding guava as a management tactic against ACP were difficult to make due to persistent nematode problems and freeze damage to guava, which could have interfered with the production of guava volatiles responsible for deterring ACP infestations. Conversely, citrus nursery trees interspersed with guava did show reduced HLB incidence and disease progression over time. However, vector and disease reduction resulting from guava intercropping in citrus nurseries was not adequate to recommend it as a management strategy.