Citrus Greening (Huanglongbing) Identification and Management

Citrus Greening
(Huanglongbing)
Disease
Identification and
Management

Economic Losses
Asia
• Disease endemic – tree life 8-12 yr, yields low,
fruit small and/or unmarketable; yields better
in cooler, highland areas
South Africa
Greening manageable by healthy nursery stock,
removal of positive trees, psyllid control; most
severe in cooler upland areas.

Brazil
• Disease discovered in 2004 and now
widespread, but not having a major impact on
yield yet
• Management includes use of disease-free
nursery trees, removal of affected trees and
psyllid control

Names
• Yellow shoot (China) huanglongbing
• Likubin (Taiwan)
• Dieback (India)
• Leaf mottle (Philippines)
• Vein phloem necrosis (Indonesia)

The Pathogen
• Phloem-limited bacterium
• Not in culture
• Pleomorphic (shape can vary)
• Spreads in plant slowly, but downward
movement may be rapid.

Causal Agents
• Candidatus Liberibacter asiaticus – Asian
• Ca. L. africanus - African
• Ca. L. americanus- Brazil

Pathogen Host Range
• All citrus species are susceptible irrespective
of rootstock
• Symptom severity may vary with the strain
• Highly susceptible: sweet orange, mandarin,
mandarin hybrids
• Moderate: grapefruit, lemon and sour orange
• Tolerant: lime, pummelo, trifoliate orange

Movement of the disease
• Infected plant materials that may or may not
show symptoms – citrus, Murraya?, Severinia
• By flight or wind dispersal of psyllids
• Infected psyllids on ornamentals that may not
be host to the bacterium
• Not spread by contact, tools or equipment

Vectors and Epidemiology
• Diaphorina citri - Asian citrus psyllid
- transmits Asian greening
- established in Florida
• Trioza erytreae - African citrus psyllid
- transmits African greening
- not present in Florida

Asian citrus psyllids

5 nymphal stages
10 generations / year
Life cycle takes
15-47 days
egg adult in 2
weeks at 75-80°F
Asian Citrus Psyllid

• Psyllid Adults
Field Identification

Field Identification
• Psyllid Eggs – laid on developing leaves

Field Identification
• Psyllid nymphs – feed on young tender flush

Factors Affecting Psyllid Populations
• Availability of new flush
– Psyllid nymphs can only develop on young tender
leaves
• Temperature
– Optimal temperature for development 68-85°F
– Psyllid populations do not grow rapidly when
temperatures above 90°F

Vector Relations
• Acquisition access period: 15-30 min
• Latent period: 8-12 days
• Inoculation access period: ~ 1 hr
• Acquisition by adults, large nymphs, 4 th and 5 th
instars
• Persists and reproduces in the vector for life
• Probably not passed to next generation

Symptoms
• First symptoms of yellow shoot
• Blotchy mottle or variegated type of chlorosis with
small upright leaves
• Heavy leaf and fruit drop with off season flush and
bloom
• Severely infected trees - stunting, sparse foliation, die
back
• Fruit – small, lopsided with bitter salty taste and may
not color properly

Greening Management
• Disease-free nursery stock
• Removal of symptomatic trees
• Reduce psyllid populations by biological or
chemical control
• Cultural techniques

Disease Free Nursery Stock
• Begin with clean plant material
• Nursery/budwood under screen
• Additional protection provided by soil
applied systemic insecticides

Removal of Symptomatic Trees
• Important to remove immediately
• Pruning will not eliminate the disease from an
infected tree!
• Make application of foliar insecticide spray
prior to tree removal
• Increase frequency of scouting in areas where
infected trees have been removed

Suppression of Psyllid Populations
Chemical Control
• Important to protect the early season flush
when psyllid populations are at high levels
• use soil-applied systemic insecticides on
young trees
• foliar insecticide sprays will provide control on
both young and mature trees

Suppression of Psyllid Populations
Chemical Control (soil-applied systemic insecticides)
• imidacloprid (Admire 2F, Admire Pro)
- for use on trees < 6 feet in height
• aldicarb (Temik 15G)
- application allowed only from Jan.1 – April 30
- must be applied 30 days prior to flush for
suppression of psyllid populations on mature
trees

Suppression of Psyllid Populations
Chemical Control (foliar-applied insecticides)
• fenpropathrin (Danitol 2.4 EC)
• imidacloprid (Provado 1.6 F)
• chlorpyrifos (Lorsban 4EC)
• petroleum oil (2% rate)
- Oil sprays will control psyllid nymphs present at
application but have no effect on psyllid adults which
re-infest treated plants within a few days

Suppression of Psyllid Populations
Biological Control
There are numerous natural enemies of psyllids
present that suppress psyllid populations, especially
in the summer and fall
Overuse of broad spectrum foliar insecticides will
negatively affect populations of natural enemies of
psyllids and other potential pest species such as scale
insects, whiteflies, aphids, etc…

Suppression of Psyllid Populations
Biological Control
Over 90% of psyllids nymphs are consumed by
predaceous insects such as ladybeetles

Suppression of Psyllid Populations
Biological Control
Parasitoid:
Tamarixia radiata

Cultural Practices
Removal of surrounding alternative
host plants of Asian citrus psyllid
Website listing all known host plants
for psyllid and greening pathogen
http://www.doacs.state.fl.us/pi/enpp/ento/greening/hostlist.pdf

Orange Jasmine,
Mock Orange
(Murraya paniculata)
• a preferred host for psyllids
• unlikely to be a host plant for
greening disease ?????

Chinese box orange,
Box thorn (Severinia buxifolia)
• host for Asian citrus psyllid
• can serve as a source of
the bacterium for psyllids to
become infected

Greening identification and reporting
• Greening ID is difficult; many suspects that
will be negative
• Suspects should be confirmed as possible
greening by an expert
• Report high suspects to county agent or
regulatory agency

Credits
• R. H. Brlansky – plant pathologist CREC
• M. E. Rogers – entomologist CREC
• P. A. Stansly – entomologist SWFREC
• L.W. “Pete” Timmer – plant pathologist CREC
• G. Baut – graphics specialist CREC