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Science, industry fight citrus greening disease

Peter Spyke, president of Arapaho Citrus Management in Fort Pierce, says growers missed the chance to stop citrus greening when tree removal may have worked. “They did not do that. That doomed the rest of us to living with it,” he says.    

Palm Beach Post

Peter Spyke, president of Arapaho Citrus Management in Fort Pierce, says growers missed the chance to stop citrus greening when tree removal may have worked. “They did not do that. That doomed the rest of us to living with it,” he says. 

When the citrus tree-killing disease known as greening was detected for the first time in the United States in Homestead in August 2005, some feared the end was near for Florida's signature industry.

Now, more than seven years later, the apocalypse has not occurred, but the disease that results in bitter, misshapen fruit is said to be present in every grove. Although no one knows the actual number of infected trees, many place it between 40 percent and 70 percent.

The citrus industry has undergone a sea change. Production costs are up about 40 percent in many cases, mostly due to the cost of spraying for psyllids, the insects that spread the disease, and to nutritional programs to keep trees as healthy as possible.

Primarily through a grower-funded tax on each box of fruit, the citrus industry has invested $66 million in 129 research projects run by 30 doctoral scientists looking for a solution to the disease, also known as Huanglongbing, or HLB.

But the industry continues to shrink. The state's commercial citrus acreage has shrunk to 531,493 acres as of the fall of 2012, a 28 percent decline from 748,555 acres in 2004. That's the lowest since the U.S. Department of Agriculture began the survey in 1966.

This season the USDA has revised the crop forecast downward twice since October, because the amount of fruit dropping from trees is greater than expected and the worst in more than 40 years. Growers are blaming greening and drought.

New protocol

But, Tom Spreen, a professor emeritus at the University of Florida's Institute of Food and Agricultural Sciences, said growers have come up with a whole new line of defense the doomsayers did not predict, which has allowed it to produce more fruit than it would have.

Young trees are babied in greenhouses to keep out the Asian citrus psyllid, an insect that spreads the greening bacterium. Once in groves, trees are sprayed to keep the psyllid population down.

"The total industry is working diligently to control the psyllid population, but the challenge is, the psyllid in Florida is as prevalent as the mosquito," said Ricke Kress, president of Southern Gardens Citrus, a U.S. Sugar subsidiary south of Clewiston. Southern Gardens owns groves and has the only large orange juice plant in the southern part of the state.

Southern Gardens has invested more than $6 million in research. It has planted the fourth generation of trees that contain two spinach genes that provide resistance to greening. The trees are developed in the lab by Erik Mirkov, a Texas AgriLfe Research plant pathologist in Weslaco, Texas.

The genetically modified trees and fruit will have to go through regulatory approval from the U.S. Food and Drug Administration, the Environmental Protection Agency and the USDA.

Once a disease-resistant tree is available, Kress said, chemicals to control psyllids can be eliminated.

Citrus greening disease

What it is: A bacterial disease known as Huanglongbing (HLB) or yellow dragon disease, it is one of the most serious citrus diseases in the world, and kills trees.

Origin: Farmers in Southern China first noted the presence of the disease in the late 1800s.

Florida history: In 2005, U.S. Department of Agriculture scientists confirmed the first U.S. detection of greening on samples of pomelo leaves and fruit from a Miami-Dade County grove. It is now endemic to Florida and found in every citrus-producing county.

Symptoms: Yellow shoots, mottled leaves, twig death, tree decline and reduced fruit size and quality. Affected fruit tastes bitter, medicinal and sour. Symptoms don't show up for an average of two years following infection.

How it's transmitted: Asian citrus psyllids, first found in the United States in Delray Beach in 1998, transport the greening pathogen from infected trees to healthy trees as they feed on the plant. They have mottled brown wings and sit at an angle to the shoot or leaf on which they feed.

The cure: None.

Source: U.S. Department of Agriculture Animal and Plant Health Inspection Service

Science, industry fight citrus greening disease 01/25/13 [Last modified: Friday, January 25, 2013 9:53pm]

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