The Madeleine Brand Show for April 6, 2012

California's citrus trees could be in trouble

orange tree grove

Cecilia Aros/ Flickr Creative Commons

California's citrus plants could be in trouble if a disease known as "citrus greening" spreads.

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Sanden Totten

Agricultural Technician Hector Verduzco grabs a sample of an Asian Citrus Psyllid bug. The bug is responsible for spreading the bacteria known as yellow dragon disease.

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Sanden Totten

Agricultural Technician Hector Verduzco showing off his aspirator. It's a tool used to trap tiny insects, like the Asian Citrus Psyllid.


Imagine California with no oranges, no lemons, no limes. This could be reality if state officials don’t find a way to stop the spread of a plant disease known as “citrus greening.”

The disease, also known as Huanglongbing or Yellow Dragon Disease, turns fruit into small, bitter lumps and slowly kills every tree it infects.

Part of Hacienda Heights, Calif. is currently under an agricultural quarantine after the disease was detected there last week, the first time it’s been detected in the state.

In pandemic thrillers like “Outbreak” or “Contagion,” Patient Zero is a poor sick soul coughing to death in a hospital bed. In this case, Patient Zero was a lemon pomelo tree in someone's front yard.

Tina Galindo tracks plant diseases for the California Department of Food and Agriculture. Right now, she’s searching the Hacienda Heights area for other trees that may be infected.

“So this is a lime tree and we are looking for symptoms of citrus greening disease,” she said.

The leaves of infected trees turn mottled and yellow, the fruit green and hard. The disease is spread by little flies called Asian Citrus Psyllids. Even though this particular lime tree looks healthy, Galindo wants to nab one of the bugs for testing.

“You can see how small this insect is that we are looking for. It’s just about the size of a flea,” she said.

Bug catcher Hector Verduzco pulls out a small glass vile with two tubes called an aspirator. He carefully holds one tube next to the tiny psyllid. He sucks on the other and the bug is pulled into the vile.

The bug will be sent to a lab to be tested for citrus greening. If it turns out that this bug and others have been spreading the disease, California’s citrus trees are in serious trouble.

“It’s a death sentence for the tree. There’s no cure. You can’t give them antibiotics,” said UC Riverside entomologist Mark Hoddle. “You can’t effectively prune out the disease once it’s in the tree, because it spreads throughout the entire tree. So once it’s infected it’s just a matter of time before it goes into decline and eventually dies.”

Hoddle says symptoms take years to show up, so the tiny psyllid bugs can spread the infection far and wide before an outbreak is evident. Citrus greening bacteria clog up the tree’s internal circulation, effectively cutting off nutrients.

“Basically the bacterium is starving its host of its food and that’s why you end up with yellow leaves and small, misshapen, bitter citrus fruit,” explained Hoddle.

Bob Blakely is with California Citrus Mutual, a group that advocates for the state’s $2 billion citrus industry. He says citrus greening is the most serious citrus disease in the world.

The bacteria ravaged crops in Asia, it showed up in Florida seven years ago and has since killed off thousands of the state’s citrus-related jobs and billions in potential revenue.

"The citrus industry could virtually be wiped out in Southern California if it’s not stopped,” said Blakely. “It’s a huge challenge for those of us in California because one in about every four backyards has a citrus tree in it.”

Blakely adds that researchers are developing a resistant strain of tree using spinach DNA. They’ve also released a tiny wasp that kills the disease carrying psyllids, but so far, there’s no easy answer.

The California Department of Food and Agriculture’s Tina Galindo knows a lot is riding on her team. They’ve already cut down Patient Zero — the sick lemon pomelo tree — and shipped it to a lab for analysis.

So far, that’s the only known case of citrus greening in California. Her theory is that plant picked up the sickness from an imported graft, not from an infected fly.

“Hopefully we found the one needle in the haystack and we will be able to prevent it from spreading as well,” said Gallindo.

If she’s right, California citrus growers have dodged a bullet. For now, Galindo’s team will keep looking over lemons and observing oranges, to make sure there aren't other trees sick with citrus greening.


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