Research: Asian Citrus Psyllid
Citrus greening disease or “huanglongbing” (HLB) is caused by bacterium Candidatus
Liberibacter asiaticus, vectored by the Asian citrus psyllid (ACP), Diaphorina citri.
The bacteria are acquired primarily by the immature stage psyllid (nymph) when it
feeds and develops on infected trees. Eggs are laid on young flush were nymphs develop
to adults which spread the disease. Acquisition by adults occurs but at a much reduced
rate. The psyllid was first found in Florida in 1998 and the disease in 2005. Both
have spread rapidly throughout the state and are also found throughout Asia and
the Neo-tropics. The first sign of infection is often one or more yellow shoots
from whence the name huanglongbing in Chinese. Symptoms spread throughout the tree
and a gradual decline ensues resulting in dieback, leaf and fruit drop. The process
is hastened by continual inoculation by infected psyllids and appears to be mitigated
by foliar applications of micronutrients that seem to somewhat compensate for reduced
efficiency of the phloem that ultimately impacts the tree’s ability to absorb and
transport these materials from the soil.
HLB represents the greatest plant health problem to ever challenge the Florida citrus
industry. Vector management is the primary means of slowing spread of the disease
from tree to tree and even within trees. Our focus then is on the integrated management
of ACP using a combination of tactics aimed at economical pest suppression with
minimum impact to beneficial insects and mites. The major elements of this program
include the “dormant” spray directed against a declining, overwintering adult ACP
population at a time when much of the beneficial fauna is absent from the orchard.
Significant reductions of ACP of up to 6 months have been observed following a single
application in January. We are also working to improve the performance of systemic
insecticides applied to the soil, especially to protect young trees, and other selective
alternatives such as frequent, low volume application of horticultural mineral oil.
We have also developed a “tap” sampling method for efficiently monitoring pest and
beneficial populations to help with decision making during the growing season, and
are working with other scientists at University of Florida, USDA-ARS, DOACS-DPI,
and several institutions outside of Florida on methods of mass rearing and release
of the parasitic wasp Tamarixia radiata and other psyllid natural enemies
to reinforce or in some cases reestablish biological control. We are working with
the industry toward area wide application of these tactics beginning with a successful
cooperative dormant spray program in Southwest Florida during the 2008-09 and 2009-10
seasons. Information on all this and more can be found on this website as part of
our strong commitment to actively inform a citrus community in the search of solutions
for this and other pest problems that impact citrus production.