Citrus greening disease threatens the entire citrus industry

I always look forward to this time of year when citrus supplies are plentiful. My favorite one has always been the tangelo, but that is changing. It’s not because I like them less, it’s because they are nowhere to be found.

The reason for this is the citrus greening disease, sometimes called huanglongbing disease or HLB. It’s caused by a bacterium spread by a tiny sucking insect called a psyllid. Bacterial diseases are difficult to control in plants.

Bacteria reproduce extremely fast, so host plants must be treated constantly. That’s impractical for large acreages. The bactericides and insecticides also must be systemic and enter the plant tissue to be effective. Chemicals also can’t be toxic to the consumer.

Tangelos are among the most susceptible of all citrus types. Grapefruit, key lime, and clementine are more resistant. If you have been surprised to not find tangelos in the store, there’s good reason.  There are none.

Perhaps you’ve noticed more mandarin oranges at grocery stores than in past years. Mandarin types like clementines are somewhat more tolerant to the disease, and in recent years more farmers have planted them.

Once a tree is infected with HLB, there is no cure. The fruit yields in Florida are a fraction of what they were in 2000. Fruit prices have been on the rise to compensate for decreasing yields and everyone has suffered.

Plant pathologists have been working hard for over a decade to develop citrus that is resistant to these bacteria. They’ve also initiated programs to hinder the psyllid insect that carries them.

So, what does citrus greening disease actually do, you ask? Trees infected with the bacteria produce fruit that stays green even after it is ripe. It’s also bitter and poorly shaped. Sugar can’t be transported properly inside the plant, so fruit quality is poor and energy to the entire plant is limited. Infected trees usually die within a few years.

A few decades ago, another bacterial disease called citrus canker ravaged Florida. It’s still a concern. Entire orchards were quarantined and destroyed under government supervision. Many farmers were ruined, but it was minor compared to the present citrus greening problem.

Trees infected with that disease had fruits that had unsightly surface blemishes. They still were acceptable for much of the juice market. Citrus greening is different. Fruit quality is unacceptable for any human consumption. Sugars won’t translocate to the fruit normally.

Controlling both these diseases involves reducing the amount of disease inoculum available. That means destroying infected trees. Backyard gardeners must comply too. If either of these diseases is detected on any tree in a commercial orchard, nursery or private residence it must be destroyed.

Until recently the disease was limited to Florida and Texas in the US. It has now spread to California. Their problem has been less severe, but I suspect part of the reason is that the climate is less ideal for vector and pathogen growth.

Florida’s climate is hot and humid, while citrus producing areas in California are hot but far less humid. Whatever the case, we’re facing several more years of reduced citrus quality and yield. That’s a shame.


Ted Manzer teaches agriculture at Northeastern High School.

About tedmanzer

I grew up in Old Town Maine and got a B.S. at the University of Maine in Plant Sciences/ minor in Botany. From there I moved to West Virginia and earned a M.S. in Agronomy at WVU. I also met my wife there. She grew up in rural WV as the daughter of tenant farmers who raised cattle and hogs. Their lifestyle at times was one of subsistence and I learned a lot from them. I've always been a foraging buff, but combining my formal botanical knowledge with their practical 'Foxfire-type' background opened up my eyes a little more. I recently retired from teaching high school agriculture after 25 years teaching with my wife. Until recently I wrote a weekly nature/foraging column for the local paper ( I also have written several Christian nature/adventure novels that can be purchased on Amazon in Kindle format. One is a five book family saga I call the 'Forgotten Virtues' series. In the first book, Never Alone (presently out of print), a young boy comes of age after his father dies in a plane crash, and he has to make it alone. The second book, Strange Courage, takes Carl from his High School graduation to his recovery from a nasty divorce. The third book, Second Chances, takes Carl from his ex-wife's death and the custody of his son to his heroic death at age 59. The fourth book, Promises Kept, depicts how his grandchildren react and adjust to his death (this one is not yet published). In the final book, Grandfather's Way, his youngest and most timid granddaughter emerges from the shadow of her overachieving family and accomplishes more in four months than most do in a lifetime. I use many foraging references with a lot of the plants I profile in these articles in those books. I also wrote a romance novel titled Virginia. It is available on Amazon and is a different type of romance from a man's perspective.
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3 Responses to Citrus greening disease threatens the entire citrus industry

  1. tonytomeo says:

    How odd that the most susceptible citrus is a hybrid of two of the least susceptible. Tangelos are hybrids of grapefruits and clementines (Mandarin oranges or tangerines).

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