California Without Citrus

Last week, after the tour of the UCR Citrus Collection, my friend Russ of LA Farm Hands and I drove across town to see history. We visited the lone survivor of the two original California Washington navel trees, planted in Riverside in 1873, and progenitor of all navel oranges in California. All of them. If you live in California and have a navel orange in your yard, generations ago, someone took a cutting from this tree or its sister, grafted it onto other rootstock, then did it again and again until finally onto the rootstock that is growing in your yard. You are, in fact, growing this tree, or part of it. Millions of parts of it are spread across the state. If you are eating a navel from California, even if you're across the country, you are eating fruit from this tree. This tree changed California history, and it changed our nation's diet.

In order to keep this ancient tree alive, its caretakers have added new rootstocks through the years. You can see by the strangely rooting trunk: those aren't roots, those are rootstocks planted close to the tree and grafted into the tree. The rootstocks have saved it from the rotten old, original trunk.

This tree has lived for almost 140 years. But now, it may not make it 140 more. It may not even make it two more.

In 2008, scientists discovered the the Asian Citrus Psyllid had broken through California's green curtain and onto her citrus; the psyllid isn't pretty, and though it will damage young growth, it won't kill it. The problem with the Asian Citrus Psyllid making its way to California is what has historically followed the psyllid, the virus known as Citrus Greening or Huanglongbing. The psyllid is the primary carrier of the virus that slowly kills the tree and makes it a source of more infection for more trees. It's incurable. It has destroyed 100,000 acres of Florida citrus, devastated the Brazilian citrus industry, and last week, it was discovered here.

I found this excerpt from "California braces for a deadly stalker of citrus" in today's Los Angeles Times particularly frightening:
Wingtack Wong, who with his siblings owns Temple Garden Center in El Monte, is sadly familiar with huanglongbing. He worked for the agricultural commission in China's Guangzhou province when the disease arrived there in the 1960s. He remembers the commission tried everything from pesticides to experimental cures to stop it, but by the 1980s and early '90s, the disease had traveled slowly north, killing all the citrus.

A wiry man who usually bustles around his sunny nursery answering three questions at once, Wong sat down to speak of huanglongbing.

He recalled a farm famous for "fields and fields of mandarins."

"One yellow leaf tuned into an entire yellow tree, the fruit shriveled up and slowly the rest of the trees turned yellow, and then it was all gone," he said, slouching in his chair.
Dr. Tracy Kahn, the curator of the UCR citrus collection, told us last week that the tree in which the disease was found had multiple grafts, likely smuggled in illegally. The recent news reports the tree was a Meyer lemon with a Chinese pummelo grafted on it. The man who grafted the tree says he received the budwood for the pummelo from a fellow gardener in his church. Though the grafted pummelo may not have been the source of the virus, it likely is. If it is, that means that there is another pummelo (maybe more than one, along with other other trees on which it has been grafted) out there that is sick.

California is worried, rightfully. I'm worried. Dr. Tracy Kahn was worried when she was talking to us, too, but she was also hopeful. She told us careful monitoring can help us catch any other diseased trees quickly, and California has already released a predator for the psyllid that will help keep its population in check; however, she implored us to share information, especially to non-English speakers, and she also forbade us from grafting any citrus budwood, whether we are inside or outside the quarantine area. She reminded us citrus relatives were also carriers, and one that commonly shows up at farmers' markets, Asian markets, and produce swaps has no place in California: curry leaf. (There are no legal sources of curry leaf in California. Everything that is here has been imported and shared illegally.)

So, what do we do?
  • Read this.
  • If you're in the quarantine zone, do not remove any citrus from your property. Do not even put it in the trash. My best suggestion, if you can't eat or preserve it, is to bury it deeply. 
  • Whether or not you're in a quarantine zone, do not graft any other citrus material onto your trees.
  • If you want more citrus trees, make sure you purchase trees that are tagged by the state as free from evidence of psyllid activity and disease.
  • Consider supporting California citrus by removing ornamental citrus relatives from your property; both curry leaf (illegal!) and orange jasmine (lovely!) are great temptresses of the psyllid, and remember, the disease follows the bug.
  • Every time you move from working on one citrus tree to another in your garden or between gardens, even if you think your property is free from virus, sterilize your tools. A quick dip in alcohol will do.
This doesn't have to be the end of California citrus, but to keep it from becoming so will take the effort not only of every citrus researcher and farmer in the state, but every home gardener too.


Jeez, Christina. We were recently making light of the strict laws about bringing produce and plants into California with a friend, a former Californian herself. But this shows why it is so important. Good luck!
Petrea Burchard said…
I didn't know. If it weren't for you and Elizabeth, I still wouldn't. Thanks for such clear instructions--the what, and also the why.
Anonymous said…
I have a curry leaf tree, a seven year resident. Won't bring the leaves to the swap anymore, not that they attracted much interest.
I now want to pay homage to the Eve of citrus

BTW: They found the bug in Highland Park. Disturbing. I had heard nothing about this until that Patch article. Timely in that I'm getting ready to do an post on feral orange groves (I like to keep an eye out on them) one step ahead of the developer's wrecking ball

Also disturbed to discover Mock Orange on the watch list. The curry tree - is that the obnoxious tree you see taking over all unkept yards?
Christina said…
PA: I think what you're probably seeing is sumac, which has the same leaf pattern as curry leaf, but isn't related.
Dan Willey said…
Great article! The future of citrus in California is not looking so great since the Asian Citrus Psyllid has been moving north and has now been found in a high-risk area of San Jose. The current technology for detecting HLB does not work well.

I have created some resources to teach about grafting citrus with budwood from disease-free source trees that I hope will be helpful in avoiding spread of the disease:
Bud Grafting Citrus Trees (Step-by-Step with photos)
Bud Grafting Citrus Trees (Video)

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