Citrus greening is a bacterial disease that threatens the entirety of the citrus industry in the U.S. and has already killed 90,000 trees in the state of Florida. The disease progresses rapidly and blocks the trees’ ability to translocate water and nutrients. One symptom of the progressive disease is the emergence of partially green fruit. Asian citrus psyllids are the carriers of this potential plague which threatens the citrus industry and are now being cultivated by scientists in California in order to develop an antidote. The psyllids suck up the bacteria as they feed on the tree and transfer the disease from tree to tree. Biological control (biocontrol) is the control of pests by interference with their ecological status, as by introducing a natural enemy or a pathogen into the environment, and this is an idea being put into play to combat this citrus threat. Tamarixia radiata is a flea-size parasitic wasp from Pakistan that attacks Asian citrus psyllids and has already been released into the California environment by the thousands in the hopes that it will help control the psyllid issue.
The U.S. Department of Agriculture has promised funding of up to 1.5 million dollars to ramp up the wasp program next year, the goal is to release approximately 1 million wasps per year.
California is desperate to avoid the fate of Florida, as 80 percent of whole fruit sold in the United States is produced there. This would be a devastating blow to the economy and ecology of California with echoing repercussions felt across the country. Asian citrus psyllids were first identified in Florida in 1998 and citrus greening hit Florida hard in 2005. It has since spread to Georgia, Texas, Louisiana and is also killing trees in Central and South America, Africa and Asia. Although the psyllids have already migrated to California, agricultural inspectors have only found one case of citrus greening at a single residence south of Los Angeles on an illegally imported orange tree. Because it can take up to two years for a healthy tree to begin to show symptoms, the psyllids and disease needs to be identified and quarantined quickly and efficiently. For now the CA Department of Food and Agriculture with federal support, are focused on killing and controlling Asian psyllid populations by eradicating as many as possible. While it is in the interest of the citrus producers to identify and control disease there are more than 2 citrus trees per residential property in southern California, so a greater danger lays in the disease gaining a foothold in the suburbs. Insecticidal sprays are impractical for this level of control, the hope is that the parasitic wasp population will spread to the yards and properties of homeowners. While a wasp hive on your landscape may sound less than ideal this species is less than a millimeter long and their stingers are not strong enough to pierce human skin.
Citrus groves may seem like someone else’s problem to us, but if this disease goes unchecked it may have a domino effect on the ecosystem and definitely the economy. Also, this can be seen as an allegory to topics of importance on this blog; buy and plant native species, continue to monitor and care for your plants, controlling disease and pests on your property affects your community and the ecosystem. Consult your arborist with any questions or concerns, and develop a plan to keep your landscape and your community healthy and safe.