Suppressing Psyllids Could Curb Citrus
Disease By Alfredo Flores February 1, 2007
To help citrus growers manage the crippling disease called citrus
greening, two Agricultural Research Service (ARS) units in Fort Pierce, Fla., are
investigating a range of strategies. One involves developing controls for the
Asian citrus psyllid (Diaphorina citri Kuwayama), which is a major
carrier of the disease.
The tiny brown psyllid was first spotted in Florida in 1998. Discovery
of citrus greeningalso known as Huanglongbing, or HLB
diseasefollowed in August 2005. The characteristic yellow shoots, mottled
leaves, and degeneration of vein phloempart of trees' vascular
systemare caused by the Candidatus Liberibacter asiaticus
bacterium that is spread by psyllids as they feed.
With HLB attacking all kinds of Florida citrus, several strategies are
being developed by scientists in the
Subtropical Plant Pathology Research Unit, led by plant pathologist
Gottwald, and in the
Insects Research Unit, led by entomologist
The ARS researchers believe that an integrated HLB management program
incorporating cultural, chemical and biological control strategies will have
the best chance of success. Program components will include the removal of
infected trees and special replant strategies, along with active psyllid
control. To develop an integrated program, scientists will conduct
epidemiological experiments testing the different management components, as
well as pursue an array of approaches to maximizing biological control of the
The psyllid is already known to be subject to natural control by lady
beetles, syrphid flies, lacewings, spiders and one parasitoid species,
Tamarixia radiata. Another parasitoid species has been found to attack
the psyllid in Asia, and ARS is working with the
Florida Department of Agriculture and
Consumer Services to import this promising candidate for testing.
Another intriguing approach is trying to create citrus trees that are
partially deciduous during some periods of the year. Since psyllids need leaves
to feed on and reproduce, eliminating leaves at a certain time of year would
eliminate the psyllids as well. Researchers are also working with Vietnamese
and Australian scientists, who have indicated that interplanting citrus with
guava almost entirely negated infestations by citrus psyllids, the vector of
the disease, and as a consequence the citrus trees remained free of HLB.
about the research in the February 2007 issue of Agricultural Research
ARS is the U.S. Department of
Agriculture's chief scientific research agency.