Thursday, September 15, 2022

Citrus Greening Disease

Global fight rages against HLB

Citrus growers all over the world are fighting against HLB, short for huanglongbing, or citrus greening disease.

However, the approaches vary, said Fred Gmitter, professor of horticultural sciences at the University of Florida’s Citrus Research and Education Center.

For example, Gmitter said Brazil has very large citrus plantings and that has colored how they approach the disease.

"They’ve done things like spraying the borders of huge properties on a weekly basis, because the bug comes to the edge of the grove first, and then it moves,” he said. “So, if you can kill it when it lands on the edge, you know, you're that much ahead.”

In China, Gmitter said there's always been a fair amount of research going on with HLB, noting that Chinese scientists are exploring genetic resistance.

The Chinese approach to HLB pairs grove care and economic investment with expected grower returns.

“If you look at some of the top provinces that produce citrus, they're actually places where there's a lot of HLB. If you follow economics, you'll see they have a period of time where there are not many citrus trees in the ground anymore because of the disease,” he said. “Then, suddenly, the prices for fruit go way up. And so, some more people get in, and they're making money, and they're taking better care of their groves, which is critical.”

With that, production increases and there is more fruit than demand, and the prices go down.

Lower prices will prompt growers to stop investing in their growth and management, and that causes a resurgence of the disease, he said.

“If you look over the last 50 to 60 years, as I have in some of the production figures, it's an up and down, and they just keep going up and down, up and down, up and down."


Citrus regions that are free from HLB include Australia and the Mediterranean region. “There are a few locations in Mexico where it seems to be held at bay, but most of the rest of the world is living with it,” Gmitter said. “Japan is free of it on the main Japanese islands. But if you go down to Okinawa, they have it there."

Greening was perhaps first identified in India at least about 150 years ago.

“They didn't quite know what it was," he said. "And they had different names for it. And ... maybe 120 years ago, they started describing plants that had the same symptoms in China and southern China and into Taiwan and Southeast Asia.”

At one point, some thought it was a nutritional deficiency.

“This was 100 years ago. We didn't even know what DNA was, so descriptions in a time where the science wasn't quite at the point it is today, where we can understand that it's a bacterial disease,” he said. “It goes back that far.”


Gmitter said CUPS, or citrus under protective screens, is a growing trend for grapefruit and mandarins, but it won’t be an answer for the orange juice industry.

“The price that you can get for oranges for juice, you know, isn't as high as the price you can get for, let's say, a premium red grapefruit right now that's being produced,” he said. With tens of thousands of dollars in production costs per acre, whatever is produced needs to be really high value so growers can make money.

“That’s what it is all about,” he added.

Gmitter said researchers have been selecting varieties for HLB resistance in the environment for several years.

“There are some things that we've identified that are really quite tolerant to this disease in the field, and some of those produce fruit that is very similar to sweet orange; they're not technically sweet orange,” he said. “They're quite a bit like sweet orange, except they have higher degrees of tolerance of HLB.

"We just had one of these approved for release by the university [earlier this year],” he continued, noting that the variety isn’t named yet.

The variety stood out, thriving and producing good-quality fruit while many other selections “went down the tubes,” he said. “That’s all we can say about it. We haven't proven it on a massive scale because, really, it's just been selected in the last four years, after 12 to 15 years of HLB onslaught.”

The variety produces fruit that looks like an orange, with incredible orange-red color, and the flavor has some tropical notes that score better than oranges, Gmitter said.

In addition to the unnamed variety, the University of Florida has developed some seedless lemons.

“Lemons are a kind of citrus that tolerates HLB pretty well if you take good care of them," he said, "and so we have some seedless lemon options that also were selected for peel oil production."

In addition, Gmitter said the University of Florida has some new sweet oranges that are showing greater tolerance of HLP than our standard run-of-the-mill varieties.

“Again, it gets to the same point of, well, how much information can you tell me how secure will my bet be? If I put my money on this, what guarantees can you give me that I’m going to win this bet?”

Under current circumstances, just a small handful of growers are going to take the leap of faith and give the new variety a shot, he said.

Once that happens, and the experiment is successful, the rest of the growers will follow.

“It’s an interesting exercise in human psychology," he said.

Because of HLB and other challenges, Gmitter said Florida is never going to be the juice orange giant it once was, but the state’s growers have some real opportunities.

Whether it be fruit from CUPS or new fresh-fruit varieties that are going to be highly tolerant to HLB, Gmitter believes growers will make money with citrus in Florida.

In addition, researchers and growers will learn about how to feed and care for infected trees, he said.

“You put all these pieces together, and there are going to be people who are going to do it because the people who are still around are really the hardcore of the industry,” he said.

Source: The Packer