Two Western scientists hope the two finds of citrus greening disease (Huanglongbing or HLB) in Texas in January will provide valuable information to help the California and Arizona citrus industries prepare for the inevitable outbreak of the deadly tree disorder in the West.

The Texas Department of Agriculture in late January confirmed the state’s first case of HLB in a commercial orange grove in San Juan in the Rio Grande Valley. A second disease find was confirmed days later in a grapefruit grove in the same area.

“Finding Huanglongbing disease in Texas means finding the disease is much closer to California,” said MaryLou Polek, California Citrus Research Board (CRB) vice president of science and technology, Visalia, Calif.

With HLB moving closer to Western groves, California’s citrus industry continues to fight an uphill battle against the disease that already could be present in the Golden State.

“Huanglongbing disease could already be in backyard citrus in Los Angeles,” Polek said.

Large numbers of the Asian citrus psyllid (ACP), Diaphorina citri, the primary vector of HLB, are now in the L.A. basin. 

“A single citrus tree in the L.A. basin area can have hundreds of psyllids,” Polek said. Funding shortfalls and large psyllid numbers are why some insecticide treatments in the metro L.A. area have been curtailed.

“It was fighting a losing battle,” Polek said. “The new treatment strategy is designed to re-deploy limited assets to allow the greatest protection for commercial citrus growers. We are concentrating treatments in the outlying areas particularly the corridors leading to commercial citrus.”

Psyllid numbers have exploded in California since the first insect was found in the summer of 2008 in a backyard citrus tree in San Diego County. In 2011, 13,967 psyllids were found in California in many repeat locations, according to Steve Lyle of the California Department of Food and Agriculture (CDFA).

More than 1,200 psyllids were found in the first 20 days of this January alone; 801 insects in Los Angeles County, Lyle says. Almost all of the psyllids have been found in residential citrus.

A few psyllids have been found in traps in commercial groves in Riverside and San Bernardino counties, but not in the major commercial citrus counties of Tulare, Fresno, and Kern.

Candidatus Liberibacter asiaticus is the bacteria associated with HLB disease and can be carried by the psyllid. HLB attacks the citrus tree’s vascular system and reduces water uptake and disrupts plant nourishment.

HLB-infected tree symptoms included mottled and yellowed leaves which can take two to three years to appear. The fruit can become misshaped, bitter tasting, and unmarketable.

No cure

There is no cure for HLB — the most deadly citrus disease in the world. Host plants for the disease include, grapefruit, orange, lemon, tangerine, and orange jasmine.

Polek concurs with other Western citrus leaders: It is a matter of when — not if — HLB is found in California and Arizona.

“My hope is researchers will find solutions before HLB gains a grip in California citrus,” Polek said. “It is a race now. We are at the final few laps. It’s getting a little tense.”

Polek says ongoing HLB-psyllid research is short- and long-term based. In late January, citrus and pest scientists from across the U.S. submitted a five-year, $10 million grant request to USDA to study potential solutions.

HLB is found worldwide in various climates. States known to have the disease include Florida, Georgia, Louisiana, South Carolina, and now Texas. So far, California and Arizona are, by the book, disease free but both have multiple psyllid finds.

In 2005, Florida officials detected HLB in the Sunshine State; the first HLB find in the U.S. The first psyllid arrived in Florida in 1998.

The University of Florida reports HLB has reduced Florida revenues by about $3.63 billion and eliminated 6,611 jobs by reducing orange juice production since —all since 2006.

According to the National Agricultural Statistics Service, Florida is the nation’s largest citrus producer with 503,000 bearing acres during the 2010-2011 crop year with an economic value of $1.57 billion. California follows with 267,400 acres — a $1.3 billion value. Texas ranks third at 27,300 acres worth $70 million; followed by Arizona with 13,500 acres and a $38 million value.

HLB was found in Mexico several years ago and has quickly spread across the country. Mexican HLB finds are within several hundred miles of California and Arizona.

Of Arizona’s 13 psyllid finds, one was trapped in commercial citrus in Yuma County.  The others were in residential citrus. Arizona’s first find was in San Luis in Yuma County in the fall of 2009. A psyllid was captured last year in a trap just north of the Nogales port of entry (Santa Cruz County). The latest find was in Pima County last December near I-19 near Continental.

Polek’s first concern is the most common path travelled by the psyllid — along major transportation corridors and at U.S.-Mexico border crossings. In addition, budget cuts by states have made psyllid control more difficult.

“We are very concerned as funding for border inspections to check for the psyllid and other pests and diseases has been cut in California, Arizona, and Texas,” Polek said.

In California, the CRB has increased trapping efforts especially along the routes near packinghouses. The CDFA has increased the collection of plant tissue samples to check for HLB; up from 1,000 total samples last year to more than 2,000 samples in the first two weeks of January.

The CRB Diagnostic Lab in Riverside, Calif., has agreed to assist CDFA in analyzing psyllid and plant samples for the presence of HLB-associated bacteria. Lab costs are paid by a commercial citrus grower assessment on field boxes of fruit through the Citrus Pest and Disease Prevention Program.

On close watch for HLB-ACP in Arizona is Glenn Wright, University of Arizona citrus specialist, Yuma, Ariz. About 75 percent of Arizona citrus is grown in Yuma County; about 75 percent are lemons.

Wright says Florida’s HLB experience allowed Texas to better prepare for HLB. California and Arizona will learn valuable lessons from Texas’ psyllid-HLB experiences. “So far it looks like the Texans have done a good job as they had time to plan following the finds in Florida.”

500-pound gorilla

The citrus researcher says the 500-pound gorilla question is how was HLB brought into Texas? The adult psyllid hitchhikes on fruit in bins and on semi trucks. There is concern the disease may have been on Mexican limes imported from Mexico to Texas. HLB has been found in Mexico in Mexican lime production areas.

On Dec. 7, 2011, Ray Prewett, president of Texas Citrus Mutual, sent a letter to USDA-APHIS Administrator Gregory Parham expressing concern that imports of Mexico-grown limes into Texas could have psyllids carrying the HLB bacterium.

Prewitt’s letter said HLB was in 17 of Mexico’s 23 citrus-growing areas — the closest find 130 miles from Texas commercial citrus production.

Prewett said shipments of Mexican key limes from the Mexico State of Colima and Persian (sweet) limes from the State of Veracruz are of the most concern to the Texas citrus industry. Limes are a preferred psyllid host due to frequent flush cycle characteristics of lime plants.

Prewett expressed concern over the low inspection rate of imported limes. Many limes enter the U.S. through Texas’ Pharr and Progreso ports of entry. During 2010, the USDA Agricultural Marketing Service recorded 15,560 truckloads of limes entered the U.S. through the Texas ports of entry. Most of the shipments originated in the states of Colima and Veracruz.

Lime imports fall under the guidelines of the National Agriculture Release Program where only 1 in 50 loads are inspected to ensure that leaf and stem material in the shipment is within set limits. 

Prewett said adult psyllids had not been found in shipments to date. Yet psyllids could be present but not seen due to the insect’s almost microscopic size (one-quarter inch) and its high degree of motility when disturbed.

With thousands of truckloads of limes entering Texas each year from known HLB infected areas, Prewett said USDA has a responsibility to protect Texas citrus growers from an HLB infection from Mexico.

Prewett said, “We are requesting that a formal risk assessment be initiated as soon as possible to include packing house operations at the point of origin; survivability of adult psyllids under normal shipping environmental conditions; presence or absence of adult psyllids upon arrival at destination; and a determination of HLB positive or negative of any psyllids found.”

Wright says infrequent citrus inspection is also likely at Arizona’s port of entry in Nogales. “Imported limes from Mexico could be a real risk and we’re not paying enough attention to it as a citrus industry,” Wright said. “We are running into issues of people wanting continued U.S.-Mexico agricultural trade but without fully considering the disease implications.”

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