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California Citrus Fights Back

UC Riverside

On the outskirts of Northern San Bernardino you’ll find remnants of a citrus empire. Arnott Farms is just one of the many groves in Southern California. From an outsider’s point of view, it looks completely normal, but as you move inwards you’ll notice the leaves.

"You see the way that the leaf is distorted. This is called cupping where the leaf curls under. Another symptom, I call the left turn, the leaf turns like 90 degrees. So part of the leaf is growing in one direction and another part's growing in a different plane. And it twists in the middle where the damage from the pest happened."

Some of them warped, others have spiraled and for Jim Davis, a Pest Control Advisor, this could mean the trees are under attack.

Davis, who regularly checks up on the trees at Arnott Farms says this particular grapefruit grove has been exposed to a parasitic bug for several years. 

The Asian Citrus Psyllid, is a tiny bug that feeds on citrus trees and spreads the disease Huanglobging (HLB) or citrus greening. It causes significant damage to the trees and ultimately kill them. While these trees have been exposed to the bug they still have yet to show more worrying signs of Huanglongbing; including misshapen fruit, tree greening and bitter tastes.

“The HLB is kind of like mosquitos and malaria. The mosquito is not very harmful, but since it carries the malaria, the malaria’s very serious. So the bug itself is really just a nuisance. It really isn’t a pest on the trees, it doesn’t harm the trees, but if it carries this disease then that makes it very serious because no trees have been found so far to resist the disease. Every variety has died from this infection.”

Credit Natalya Estrada
Pest Control Specialist, Jim Davis talks about the difference between normal citrus leaves and citrus leaves affected by Huanglongbing in a grapefruit grove at Arnott Farms.

Huanglongbing first appeared in California, in 2008 in San Diego. However, Dr. Mark Hoddle of UC Riverside says that the psyllids are spreading to the rest of the state.

“All of southern California now, south of the Cajon Pass, is pretty much infested with Asian Citrus Psyllid. We are now getting increasing numbers of reports of Asian Citrus Psyllid finds in the San Joaquin Valley, especially around Bakersfield and Tulare. It looks like the psyllid is now moving north out of southern California and into the Central Valley, where about 80 percent of California Citrus is growing.”

If Huanglongbing isn’t contained, California’s citrus industry could take a hit.

“Once your tree has this bacterial infection, it’ll die and some estimates suggests that citrus trees will die within 5 to 8 years after being infected by this bacterium. So obviously it’s a concern for a lot of citrus growers and a lot of homeowners who enjoy picking fresh citrus out of their backyard gardens.”

This isn’t the first time the disease has swallowed up a large citrus industry. The first case of Huanglongbing, in the United States, happened in Florida where Asian Citrus Psyllids were identified in the late 90s. By 2005 traces of it were found in the fruit trees. This affected Florida’s citrus industry, causing deformations in oranges and roots. The trees eventually died leaving some Florida groves uninhabitable. Additionally, this caused millions of dollars in damages, and about 6 thousand jobs were lost to the disease. That’s something Hoddle wants to prevent in California.

“We’ve been very active about getting on top of this problem quickly, and the reason we did that is we were looking at Florida, we were looking at Texas and we saw what happened to those two states and we don’t want a repeat of that here.”

There are several methods being used to combat the Asian Citrus Psyllid, and one of those involves using its natural enemy.

The TamarixiaRadiata are tiny, stingless parasitic wasps from Pakistan, that prey upon the pysllids.

Credit UC Riverside
Close up of the Tamarixia Radiata.

Another words they are lean, mean and in this case citrus bug eating machines. It's kind of like hiring a very small team of exterminators, or what Hoddle might call little mercenaries.

“Right so that’s exactly how we look at it this. We’ve recruited mercenaries to kill Asian Citrus Psyllids in our citrus orchards and our backyard gardens.”

Other methods of controlling the bugs and Huanglongbing include several different insecticide sprays which can be sprayed once every two weeks. New methods and developments are being studied to combat the disease. UC Riverside researchers have teamed up with The California Citrus Foundation and the US Department of Agriculture to save citrus trees like the ones at Arnott Farms from further destruction.

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