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Spread of citrus pest threatens trees with disease

Issue Date: February 22, 2012
Asian citrus psyllid isn’t particularly destructive to citrus plants on its own, but it can spread a bacterium that causes huanglongbing disease, which kills citrus trees.

Citrus farmers and pest-control officials continue their work to keep the Asian citrus psyllid out of commercial citrus groves in California, but experts who spoke about the pest threat last week at the World Ag Expo in Tulare urged farmers to be prepared for the possibility of psyllid quarantines in commercial groves.

The small, winged insect isn't particularly destructive on its own, but as it feeds on citrus it can spread a bacterium that causes huanglongbing disease, also known as HLB and sometimes called citrus greening. The bacterial disease has not appeared so far in California.

It has, however, spread widely in Florida, reducing that state's commercial citrus production by at least 10 percent a year. In Texas, the first known case of HLB was confirmed in mid-January on orange trees in the Rio Grande Valley, known for its grapefruit and orange production.

The Asian citrus psyllid has also been found in Louisiana, Georgia, South Carolina, Arizona, Hawaii and Mexico. HLB has been found not only in Florida and Texas, but also in Louisiana, Georgia, South Carolina, Belize and Mexico.

Plant pathologists say the proximity of Mexico to California and the rapid rise in globalization of trade, travel and immigration make the threat of the disease entering California through infected plants or insects a serious one.

In a recent California Senate briefing, lawmakers were told Florida has lost more than 60,000 acres of citrus trees and growers there are spending more than $500 per acre on psyllid control and eradication. One projection suggested that almost all of Florida's citrus trees will be infected in seven to 12 years.

Once trees are infected, the fruit produced is not marketable and the trees ultimately die. There is no cure for HLB.

In California, quarantines for the psyllid have been established in all of Imperial, Los Angeles, Orange and Ventura counties, as well as parts of Riverside, San Bernardino, San Diego and Santa Barbara counties.

In early February, the San Barnardino County Board of Supervisors adopted a resolution supporting the state's efforts to stop the spread of the insect. In January, the Redlands City Council approved spending $38,000 to treat city-owned citrus trees to prevent spread of the psyllid.

Ted Batkin, California Citrus Research Board president, said citrus farmers should be prepared for "the call" that the psyllid has been found in or near their grove.

"Eighty percent of issues can be planned for ahead of time," Batkin said. "Have a plan in place. Know what you're going to do and take action. Know who to call."

Typically, that call would be to the county agricultural commissioner or a local pest control district, he said.

"Discuss the steps with your farm management team," Batkin advised. "Be sure everyone in your organization knows what to do. If you have to treat or clean fruit, know what procedures you'll have to follow."

Citrus nurseries have been particularly affected by psyllid quarantines. Larry Rose, field manager for Brokaw Nursery in Ventura, said that to stay in the citrus business the nursery is required to keep its propagative material under screens with positive-atmosphere entrances, which includes a vestibule with air blowers that prevent insects from entering the structures.

"That's mandatory by state and federal agencies," Rose said. "We now have citrus registration regulations and we're operating under two quarantines. It's not difficult to comply, but it costs a lot of money."

He said there are about 30 citrus nurseries in the state and that building the required protective structures costs between $2 and $30 a square foot, depending on the level of permanence and site requirements.

"Because we're in a quarantine area, we're treating all the time," San Diego County nursery operator Mark Collins said. "We don't really have any psyllids and our treatment program is so regular and complete, the problem with this pest has disappeared into the woodwork for us."

San Diego County, because of its proximity to Mexico, is under continual, often multiple quarantines for invasive insects.

"Our plan is to keep on doing what we're doing," Collins said. "Treating for the pest has become a regular part of our operation."

Scientists say a long-term solution to the vector-disease problem isn't easy to find, but there are some glimmers of hope. Researchers at the Cornell University Agricultural Experiment Station have created several orange trees, bred through biotechnolgy, that show pest resistance and could help prevent the spread of HLB.

Entomologists Mark and Christina Hoddle of the University of California, Riverside, located a parasitic wasp in the Punjab region of Pakistan about 18 months ago. The couple found that the wasp lays eggs in psyllid nymphs, killing them through feeding, before emerging as adults.

The Hoddles brought the stingerless wasps back for study and breeding. Last December, university and government researchers joined them in releasing the first batch of the wasps on the UCR campus, to see if they can provide biological control of the psyllid.

Mark Hoddle said the wasps won't eradicate the psyllid, but might reduce populations and improve chances for control using other methods. Citrus farmers would still have to treat for the pest, but control might be possible with fewer applications, he said.

(Kate Campbell is an assistant editor of Ag Alert. She may be contacted at Editor Dave Kranz contributed to this story.)

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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