Citrus Greening (Huanglongbing) Disease 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

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

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