Citing continuing Asian citrus greening quarantines in Florida and outbreaks of the disease in Georgia, Louisiana and South Carolina, USDA will step up U.S.-Mexico border inspections over the holiday season to diminish the threat of infected plants crossing Mexico ports of entry in an effort to keep Texas and California free of the same deadly disease that has cost the Florida citrus industry an estimated $300 million annually since it was first detected there in 2005.

“USDA is working closely with U.S. Customs and Border Protection to stop the infiltration of all plant material across the border that might spread citrus greening disease to U.S. soil,” reports USDA spokesman Larry Hawkins. “The approaching holiday season presents a challenge to inspectors because of the elevated traffic across the border and stepping up inspection procedures and having a plan in place will help to insure the problem doesn’t cross over to sensitive areas like the Texas Rio Grande Valley.”

Hawkins says while Citrus greening is a major problem for commercial growers in Mexico, the disease is largely limited to southern Mexico and concentrated in the Yucatan Peninsula. But it’s not infected fruit imports that have USDA concerned. Hawkins says Mexico is doing a good job fighting the disease and carefully monitors all commercial fruit production to help control the spread of the problem.

Mexican fruit is screened

“All Mexican fruit imports are screened in a cooperative effort between USDA and Mexico’s agriculture counterpart before they reach the border and are subject to further inspection on this side of the border. The real danger in the spread of Citrus greening comes from infected plant parts like leaves and twigs attached to non-commercial imports of fruit, like those brought in by visiting Mexican residents,” Hawkins says. “The holiday season sees a spike in visitors from Mexico crossing at land ports of entry and this is the time of year that U.S. Customs and Border Protection inspectors step up their efforts to monitor potential spread of infected plants, including ornamental plants like orange jasmine.” 

Citrus greening disease, or Huanglongbing (HLB), is considered the most destructive disease of citrus worldwide. It is endemic in large parts of Asia and Africa, and has recently invaded the Americas. The disease is caused by a bacterium which is transmitted by insects called psyllids. There is no cure for greening, and the lengthy latent period after infection makes eradication almost impossible. The disease reduces fruit production, destroys the appearance, taste and economic value of fruit and eventually kills citrus trees.

Devastating disease

In Florida the disease has spread to all parts of the state threatening to cripple a $9 billion-a-year industry that supplies 90 percent of U.S. orange juice. The Florida Department of Citrus predicts that citrus greening will cut Florida orange production by 5 percent to 6 percent a year until a cure is found or disease-resistant trees are developed and widely planted. That translates into cutting orange production nearly in half over the next decade.

Citrus greening is widespread in Brazil, Cuba, Belize, and southern Mexico and four U.S. states (Florida, Louisiana. South Carolina, Georgia) – but so far the disease has not been detected in either California or Texas, although the Asian citrus psyllid (ACP) is widespread in both states. The psyllid is also found in Alabama, Arizona, Florida, Georgia, Hawaii, Louisiana, Mississippi, and South Carolina.

While there have been no confirmed reports of Citrus greening in Texas or California, Dr. John da Graca, a plant pathologist and director of the Texas A&M-Kingsville Citrus Center in Weslaco, a USDA citrus testing facility, says the Asian psyllid is well rooted in both states.

“In the (Texas) Rio Grande Valley alone we have confirmed large populations of the psyllid, first detected in 2001. By 2006 we detected psyllid populations in the Big Bend area, in College Station and the Houston area, and many areas south of that line that divides the state into north and south regions,” da Graca reports.

Da Graca agrees with Hawkins that Texas and California commercial growers are doing a good job in monitoring orchards for signs of the disease and are actively involved in prevention planning and attempts to control psyllid populations. He says the greatest threat of outbreak in the state comes from infiltration of nursery stock and cuttings from infected tress and plants from out of state, a problem Hawkins says is a challenge.

Greatest threat

“Our greatest threat is from an infected tree, plant or cutting entering the state by consumers. Unknowing residents might purchase ornamentals or nursery stock from unscrupulous sellers either through a Web site or by unknowingly purchasing an infected product out of state and bringing it back for use in their yard or garden. Once an infected plant takes root, it is subject to psyllid transmission,” Hawkins says.

Pathologists at the Texas A&M-Kingville Citrus Center are currently studying methods of developing Citrus greening resistant trees in hopes of one day providing an effective method of replacing non-resistant varieties as a way to eradicate the disease, but they agree it may be years or decades before that can happen.

In addition, da Graca says a method of applying a “nutrient cocktail” to non-resistant plants is being tested in Florida, Texas and California and has demonstrated promising results.

“We have been testing this and other methods of controlling the disease and have experienced some success. But such experimental methods of fighting the spread of the disease are still a few years away before widespread application will become effective. Until then we are actively promoting psyllid control and insect reduction in hopes of staying ahead of the game, but to think Texas or California will escape Citrus greening infection in the months and years ahead are “optimistic” at best,” da Graca says. “The best method of control currently is an informed public.”

More information about Citrus greening can be found at www.texascitrucgreening.org.