Two words — canker and greening — continue to send shudders through the U.S. citrus industry.

Huanglongbing, also known as citrus greening disease or HLB, tends to turn fruit green after ripening, and is the most widespread threat. According to the U.S. Department of Agriculture, greening is “the most serious threat that the Florida citrus industry has ever faced.”

According to USDA, the bacteria that cause HLB — three species of Liberibacter — probably originated in China in the early 1900s. In countries where the disease is endemic, citrus trees begin to decline within 5 to 8 years after planting and rarely bear usable fruit.

Greening was first found in Florida in 2005, and, by 2008, it had been identified in most of the citrus growing counties in the state.

Now the disease is in Texas, detected in January. Although Asian citrus psyllids have been found in California, none tested positive with the disease.

Florida also continues to face an ongoing threat from citrus canker, a bacterial disease spread by wind, rain or contaminated equipment.

Canker, which hurricanes spread in Florida in 1986, 1995 and 1997, leads to premature leaf and fruit drop and a decline in citrus tree health and production of fruit. In addition, lesions on the fruit make it unmarketable, according to growers.

USDA ended funding in 2006 to remove canker-infested trees, as the agency decided it was no longer possible to eradicate the problem by removing trees.

For the moment, growers and shippers are working to stem the spread of such problems, and they’re reporting some success.

“We’re adhering to consumer safety regulations and are not packing any fruit that has canker,” said Al Finch, marketing director at Lake Hamilton-based Florida Classic Growers Inc., which, until 2010 was known as Diversified Citrus Marketing.

“We’re addressing the issue and complying to all food-safety regulations to assure our customers are not seeing fruit that has any problems.”

But the prevalence of canker remains a problem for Florida growers, said Richard Kinney, president of Lakeland-based Florida Citrus Packers Inc.

“It’s day to day,” he said. “Canker is spreading.”

The industry is making progress in its efforts, said David Mixon, senior vice president with Vero Beach, Fla.-based Seald Sweet International Inc.

“Absolutely,” he said. “The industry is investing a tremendous amount. There have been developments that are by far better than what they were.”

There’s also a lot of research on the psyllid, the vector that causes greening, Mixon said.

“I think next year there will be opportunities for planting new varieties that will be far better and consumer-friendly than we have in the state of Florida now,” Mixon said. “You match the right root stocks with the right varieties that can fight off some of the natural diseases and pests.”

He also said the industry is making gains in spite of the disease difficulties its faces.

“We’ve had probably the best year in recorded history for maturity and flavor in the fruit,” Mixon said. “We had fruit that was ahead of maturity standards. We had an early start and thus far the product we are shipping to the customers has been well received.”

The threat posed by the spread of greening is the biggest issue Texas growers now face, said John McClung, president of the Texas Produce Association, Mission.

“The biggest single issue we’re dealing with in the citrus industry is the relentless march of greening up from Mexico,” he said. “There’s nothing you can do about greening itself. What you can do, though, is try and suppress the Asian citrus psyllid population, because they’re the vector.”

Greening could pose a particular threat to Johnston Farms, a Bakersfield, Calif.-based grower that ships mandarins that still have stems and leaves, said Dennis Johnston, partner.

“Here’s what’s going to hurt us: When it’s here and we get in the quarantine zone, we won’t be able to ship stem-and-leaf anymore, because they’re afraid that it will carry the psyllid on the stem and leaf, even though we wash them,” he said.”

So far, California has been able to keep greening out of its citrus groves, said Andrew Brown, a grower and director with the Exeter-based California Citrus Mutual.

“The state of California and the industry itself have taken a very aggressive position from the lessons learned in Florida and globally, in psyllid-prevention,” Brown said.

Bob Blakely, the citrus mutual’s director of industry relations, said growers are winning the battle.

“We’re certainly having to keep up the communication effort and keeping the awareness level high, especially in the urban areas,” he said.

Research is underway to introduce natural enemies to fight the psyllid, Blakely said.

“We’re hopeful that they allow us to have an alternative to pesticide treatments sometime in the future,” he said. “It’s not going to replace the treatments immediately, but we are hopeful that over time we’ll be able to establish some natural enemies that will help us.”