Greening Disease Threatens Texas Citrus

L to R:  Ruth Sagehorn and Virginia Schuerman look at entries in the citrus fruit exhibit at the Citrus Fiesta in Mission on Saturday Jan 28th, 2012.
L to R: Ruth Sagehorn and Virginia Schuerman look at entries in the citrus fruit exhibit at the Citrus Fiesta in Mission on Saturday Jan 28th, 2012.

On Jan. 13, the first-known case of citrus greening disease in Texas was confirmed on a Rio Grande Valley orange tree. The tree showed the telltale signs: undersized, discolored fruit and curled, mottled yellow leaves.

The one case in a San Juan grove became 14 trees in two separate groves, and the outbreak brought the Valley’s citrus harvest season to a halt, as the United States Department of Agriculture investigates how far it had spread. After getting the go-ahead, quarantined growers, pressed to move the last of the year’s oranges to market, cautiously resumed harvesting on Feb. 1. But they fear the disease could spread and seriously damage their industry.

Steve Lievens, who grows Rio Star grapefruits and Valencia oranges in the groves his father established in 1950, worries about being able to identify the disease. 

“There’s a lot of difference between looking at the greening on a slide show or on some laminated cards and looking at it out in the field,” Lievens said. “We’re going to have to really school ourselves hard to say with confidence we feel like a tree does or doesn’t have greening.”

Greening disease is caused by a bacterial pathogen that is transmitted to the trees by an insect, the Asian citrus psyllid. The disease, which is harmless to humans, starves citrus trees by clogging their vascular systems with bacteria, preventing the transport of sugars and other nutrients. The tree eventually dies.

 

The disease’s latency period can last up to five years, making it difficult to detect. Greening disease hammered Florida’s citrus market in 2005 and has cost the state more than $3.6 billion in the past five years. Florida’s troubles persuaded most Texas growers, who produce about $70.9 million worth of citrus a year, to spend more than $100 per acre to spray for psyllids.

“We knew this was coming, just not when,” said Juan R. Anciso, an associate professor at the Texas AgriLife Extension Service. A quarantine imposed by the Texas Department of Agriculture bars transporting citrus nursery trees, stems and leaves outside of a five-mile radius of where the disease is found.

Under the quarantine, cleaned fruit can be transported, but until Feb. 1, growers voluntarily stopped the harvest until all the regulatory actions were taken to ensure that transporting the fruit presented no added risks. A USDA survey of plant samples from Valley citrus trees will show how widespread the disease may be.

Paul Heller, a grower and production manager for Rio Queen Citrus, said Valley citrus experts are especially concerned that citrus trees in backyards won’t be sprayed for psyllids and will become havens for the disease.

“It’s really easy to monitor what we’re doing in our own groves, but when you’re talking about people’s dooryards, it's much more of a challenge to get in there," Heller said. "A homeowner enjoys a tree they produce, and they typically don’t pay a lot of attention to the tree health and nutrition, so they could be a harbor for psyllids or for the disease itself."

Heller said growers there were used to facing challenges. In 1983 and 1989, freezes wiped out entire groves.

“It’s going to change the way we do things. It’s going to cost more to produce fruit. It may have an impact on consumers at some point,” he said. “But fruit will remain available, and we’re going to do all that we can to keep producing the high-quality grapefruit and oranges.”

But Lievens said greening is not like a freeze. 

“A freeze has a beginning and an end. You know it’s coming,” he said. “With this greening, we don’t know exactly where we stand.”

 

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