Citrus Greening

(Huanglongbing)

DiseaseIdentification 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

• Trioza erytreae - African citrus psyllid

- transmits Asian greening

- established in Florida

- transmits African greening

- not present in Florida

Asian citrus psyllids

egg adult in 2

weeks at 75-80°F

5 nymphal stages

Life cycle takes

15-47 days

10 generations / year

Asian Citrus Psyllid

Field Identification

• Psyllid Adults

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, 4th and 5th

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)

• imidacloprid (Provado 1.6 F)

• fenpropathrin (Danitol 2.4 EC)

• 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

Tamarixia radiata

Suppression of Psyllid Populations

Biological ControlParasitoid:

Cultural Practices

Removal of surrounding alternative

host plants of Asian citrus psyllid

http://www.doacs.state.fl.us/pi/enpp/ento/greening/hostlist.pdf

Website listing all known host plants

for psyllid and greening pathogen

(Murraya paniculata)

Orange Jasmine,

Mock Orange

• a preferred host for psyllids

• unlikely to be a host plant for

greening disease ?????

(Severinia buxifolia)

Chinese box orange,

Box thorn

• 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