UF/IFAS Okeechobee County Extension Service

458 Highway 98 North

Okeechobee, FL 34972-2578

Phone: (863) 763-6469

E- mail:  dfculbert@ifas.ufl.edu

October 12, 2005

Feature Article - for release the week of October 16, 2005

Dan Culbert - Extension Horticulture Agent

Citrus Greening – Another Threat to Agriculture

During the past few weeks, local citrus growers have been listening closely to the mass media, fearing the much dreaded news that a new disease is in our neighborhood. Unfortunately, it’s on our southern doorstep.  On a one to ten scale, if Citrus Canker is a “three,” Citrus Greening is an imperfect “ten”.

Last week the Florida Department of Agriculture reported that some residential trees in Palm Beach and Martin Counties have been infected with citrus greening.  One of these sites is on the Martin/St. Lucie line, which puts it too darn close to our area.  It’s time to learn about this new threat to our struggling Citrus industry.

This past August, an entomologist with the Florida Division of Plant Industry was conducting a citrus pest survey in Homestead.  Two citrus trees in separate locations showed symptoms of citrus greening.  Shortly after that, another residential site of this disease was found on the Dade Broward County border. Lab tests have confirmed that we have a new battle to win.

By early last week, 161 trees on 140 properties in Miami-Dade and Broward counties have been identified with this bacterial disease, not including the Palm Beach and Martin finds.  The fear is that there is more out there, just waiting for surveys to uncover it.

Citrus greening is also known by its Asia name of huanglongbing, or yellow dragon disease.  It is a bacterial disease that attacks the vascular system of plants. Once infected, there is no cure for a tree with citrus greening disease. In areas of the world where citrus greening is found, citrus trees decline and die within a few years.  This deadly disease does not affect humans or animals, only certain plants.

The bacteria are usually transmitted by insects know as citrus psyllids.  In June 1998, the insect that carries the Asian strain of citrus greening (Diaphorina citri) was found for the first time in the US in Delray Beach; the inspector found no citrus greening infection at that time.

Because of the extreme threat to Florida citrus, the Department of Agriculture has been conducting a citrus greening survey for many years.  Once the Asian citrus psyllid was discovered here, citrus greening survey efforts were intensified.  A survey in June 2000 found two Okeechobee nurseries had plants with this insect.

State and federal officials have again intensified the survey to identify how far this disease has spread. Experts from the University of Florida and state and federal agricultural officials are quickly mobilizing to combat this threat to our agricultural industry.

Symptoms of citrus greening disease look like plants with severe nutritional deficiencies:  yellow shoots, twig dieback, tree decline and reduced fruit size and quality.   Often only a single branch is affected at first.  Older leaves develop patches of discoloration as shown in the attached photos.  The inside of the fruit is lopsided and is inedible due to poor taste. The fruit will drop off before ripening and has poor color.  

To confirm the presence of this disease, a complex molecular test is needed. Infected trees may live for 5-8 years, but never produce usable fruit. If allowed to live, the trees can provide a source of infection for other plants.  Research on how to deal with this disease is ongoing, but here’s what we know:

• A list of  the plants that can be effected by the insect vector which carries this deadly bacterial disease include all of the well know citrus fruit trees, plus a few other plants that are sometimes seen as ornamentals in our Florida Yards: orange jasmine, jackfruit and limeberry.  

·        A common landscape bush, Orange Jasmine has been implicated as a real problem plant, as it seems to be very attractive to the Greening Citrus Psyllid insect that can carry this “yellow dragon” from one plant to another.

·        The citrus psyllid has spread around the state on orange jasmine plants, and almost all new insect discoveries were in discount garden centers.

·        African citrus psyllids can fly about a mile, which is an area almost 7 times the quarantine area for citrus canker. We don’t know the distance that Asian citrus psyllids can fly.  It’s thought that if we can get rid of the insects, we may not have to cut down as many trees.

• It is thought that South Florida high risk areas include farms that supply local ethnic markets or those nurseries with a potential history of importing illegal plant material.

  Adult  Asiatic or oriental citrus psyllid Photograph by: Douglas L. Caldwell, UF/IFAS Collier County.

Please be on the lookout for the citrus psyllid insect and for citrus trees that show the symptoms described above.  As with canker, if you suspect that your plants might be affected by this disease, PLEASE DO NOT BRING CITRUS SAMPLES TO OUR OFFICE! Call us and talk one of our agents or Master Gardeners, who will discus your situation, and if necessary, have appropriate authorities visit your site.  With your help, we can slay this yellow dragon.

I’ve placed more information on our Okeechobee web page, http://okeechobee.ifas.ufl.edu.  If you need additional information on Citrus Greening, please email us at okeechobee@ifas.ufl.edu or call us at 863-763-6469.  Local residents can stop by our office at 458 Hwy 98 North in Okeechobee, and visit our Okeechobee County Master Gardeners from 1 to 5 PM on Tuesday afternoons.  

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Trade names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.  Florida Cooperative Extension Service / IFAS / University of Florida.  Larry A.  Arrington, Dean Last update: 03/23/2006 .  This page is maintained by Dan Culbert 

For More information  

Citrus Greening Hotline 1-800-850-3781  (Florida Dept. of Agriculture)

Web Links:

Florida Department of Agriculture-Division of Plant Industry FDACS/DPI  - Huanglongbing (HLB) / Citrus Greening Disease Home page :  http://www.doacs.state.fl.us/pi/chrp/greening/citrusgreening.html 

Maps of areas confirmed with Citrus Greening: http://www.doacs.state.fl.us/pi/chrp/greening/cgmaps.html 

Nursery Growers -  restricted shipping of nursery stock: http://www.doacs.state.fl.us/pi/chrp/images/nurserymemo3-14-06.pdf

Southern Plant Disease Network (SPDN) page: Citrus Greening / Huanglongbing (Liberibacter asiaticus):  http://spdn.ifas.ufl.edu/Citrus%20_Greening.htm 

USDA site: http://www.aphis.usda.gov/ppq/ep/citrus_greening

references

Halbert, Susan, et. al. Asian Citrus Psyllid Citrus update.  Gainesville: FDACS DPI, 1/2001. http://www.doacs.state.fl.us/pi/enpp/ento/asian-citrus-psyllid.htm 

ibid.   Citrus Greening / Huanglongbing Pest Alert. Gainesville: FDACS DPI, 2005. http://www.doacs.state.fl.us/pi/chrp/greening/citrusgreeningalert.html 

Mead, Frank W.  Asiatic citrus psyllid  [Featured Creatures Bulletin] EENY-33.  Gainesville: UF/IFAS Florida Cooperative Extension Service, September 2005. [Originally published as FDACS/DPI Entomology Circular No. 180.]  http://creatures.ifas.ufl.edu/citrus/acpsyllid.htm 

Salisbury, Susan. "Bigger threat to citrus than canker found here".  Palm Beach Post, October 12, 2005. Click here for archived copy