For my March feature on a disease that is threatening the U.S. citrus industry (“The End of Orange Juice”), I spent time with researchers and growers who are working to stop this bacterial illness, which leaves fruit green and bitter and kills trees. Known as huanglongbing (HLB)  -- Chinese for yellow dragon disease -- it is caused by bacteria that hide in the salivary glands of invasive insects known as Asian citrus psyllids. The pests arrived in the U.S. in the late 1990s and have spread the disease by injecting germs into plants as they feed on sap from their leaves. There is no cure for the disease. 

Huanglongbing, which is also called citrus greening, was first spotted in Florida—the heart of America’s orange juice industry -- in 2005 and has since spread to Georgia, South Carolina, Texas and southern California. Nearly every commercial grove in Florida has been infected, costing the state billions of dollars and thousands of lost jobs. Late in 2012, the first Asian citrus psyllid was spotted in California’s commercial groves--which grow nearly 80 percent of all the fresh oranges produced in the U.S.--most likely heralding the arrival of the disease. 

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Scientists are looking at many different approaches to managing and eradicating the disease. Many say the only long-term solution will be genetic modification, which is still years away. In the meantime, entomologists are using biological control -- the practice of releasing living organisms to prey on pests -- as a means of keeping psyllid populations in check in residential areas where pesticide sprays have failed. (In Los Angeles, for example, psyllids multiplied so quickly on backyard citrus trees that state authorities couldn’t keep pace). Mark and Christina Hoddle, entomologists at the University of California, Riverside, have imported tiny wasps from Pakistan to feast on Asian citrus psyllids and have released them at more than 100 sites in Los Angeles, Riverside, and Orange and San Bernardino counties. (The wasps do not sting humans). In this video, Christina releases a vial of wasps--29 females and 15 males--on a curry bush in the parking lot of a Los Angeles hotel. (Curry is a citrus relative). The site may seem random, but in fact the Hoddles used state data to identify this site as being particularly infested with Asian citrus psyllids, which Christina calls “ACP” for short in this clip. She also talks about having previously scouted the shrub to make sure it has plenty of psyllid nymphs at the 4th and 5th instars, which are the two life stages that the wasps attack.

4 Comments

1. 1. rugeirn 11:05 AM 2/27/13

   The wasp species in question is Tamarixia radiata.
   
   There's an excellent detailed article on these wasps at http://entnemdept.ufl.edu/creatures/beneficial/wasps/tamarixia_radiata.htm with much more information than is supplied here.
   
   What I haven't seen is any sign that anyone has studied the potential downside of introducing the wasps. We know what the psyllids are up to; what will the wasps decide to do?

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2. 2. akuchment 11:22 AM 3/5/13

   rugeirn: the feature lays out more information about the wasps, this is only supplementary material. But they have an extremely narrow host range, and the Hoddles have pitted them against native flora and fauna in California and have found that they attack only Asian citrus psyllids. Here's a link for some more info from UC Riverside: http://newsroom.ucr.edu/2819

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3. 3. Anomalocaris 10:34 AM 3/6/13

   So, farewell to the orange juice industry. That will blow up the same down the border, actually, Veracruz, as far as I know.

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4. 4. jjaphx 01:26 PM 3/7/13

   as a horticulturist, i feed my citrus with the following-
   at 5#/100 sq ft, or two handfuls/plant around feeding zone- NOT ON CROWN!
   blood meal, cottonseed, low n formulation bat guano(sub bird guano, or soft rock phosphate), green sand, dolomite, rockdust, humate, prilled sulfur, then just a spoon of both kelp meal and actinoiron for each plant (imagine that rate(for kelp and iron) at 1#/100 sq ft).
   cover with 1 or 2 inches of steer manure, NOT BARK OR SAWDUST PRODUCTS (DUE TO S.O.D.). YOU SHOULD SEE IMMEDIATE IMPROVEMENT IN A FEW WEEKS.
   I DO THIS AFTER THE LAST FROST DATE EVERY YEAR.
   during the growing period, i use all season oil on the trees to control insect damage, averaging a spray every two weeks at least, set on 1 T/gal setting.
   this step would help to control this disease, but keeping your plants healthy is the better step.
   if just planting make sure you use two inches of lava sand, or 1/4" grade lava chips, with one inch of oly#2 sand to increase drainage under citrus- the #1 problem i see in the bay area in gardening. dig in 2-4" cow manure, and use manure for your topping.
   note on nitrogen use- if your tree is yellow, use blood meal, if it is light then use cottonseed. in late summer you may need to readdress plant need due to intense heat- keep it light, and balanced.
   avoid any inorganic salt fertilizers- citrus hate them, the soil structure is destroyed, and you can taste it, yech!
   if your plants are in container, just a spoon of each, then manure. citrus do not want to dry out, but do not overwater. an inch per week should do.
   good luck.

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