Farm Progress

ACP-HLB continue to force citrus nurseries indoors

Growing citrus plants in approved protective structures is becoming an economical and regulatory mandate to protect the industry from insidious pests and diseases.The top pest and disease which threatens worldwide citrus production is the Asian citrus psyllid and Huanglongbing disease.“HLB is not just one of the most devastating citrus diseases; it is the most devastating disease."

August 18, 2011

6 Min Read
<p> Asian citrus psyllid</p>

The phrase ‘Life on the Inside’ sounds like a movie profile about a convicted felon sentenced to prison without parole.

In reality, the phrase is the new status quo for U.S. citrus nursery growers and the theme of a recent workshop held in Ontario, Calif., sponsored by the California Citrus Nursery Board.

In the real world of citrus nursery production, growing citrus plants in approved protective structures is becoming an economical and regulatory mandate to protect the citrus industry from insidious pests and diseases which threaten the foundation of the industry’s future.

Today, the U.S. citrus industry employs 110,000 people from Florida to California with an economic value of $12.3 billion nationally including wholesalers, retailers, and other industries. About $4.7 billion is generated in annual wage income.

The top pest and disease combo which continues to threaten worldwide citrus production is the Asian citrus psyllid (ACP) insect, Diaphorina citri, and the bacterial Huanglongbing disease (HLB), Candidatus Liberibacter asiaticus, also called citrus greening.

The ACP is the primary vector of HLB yet the disease can be spread through grafting. ACP adults and nymphs carry the bacteria. The insect usually feeds on new plant flush.

Adult psyllids are one-eighth to one-sixth inch-brownish insects similar in size to an aphid. The insect feeds with its head down almost touching the surface of the leaf.

“HLB is not just one of the most devastating citrus diseases; it is the most devastating disease,” said Osama El-Lissy, director of emergency and domestic programs in the plant protection and quarantine unit with the USDA-Animal and Plant Health Inspection Service (APHIS) in Riverdale, Md.

“HLB will not only impact the industry economically - it will take out the industry,” said El-Lissy, the kick-off speaker at the California citrus nursery workshop. “There is no cure for HLB. An entire orchard can die in three years. That’s total destruction in a short period of time.”

The U.S. citrus industry is inundated with pests and diseases including HLB, citrus canker, citrus black spot, and sweet orange scab. Florida citrus growers battle all four organisms.

According to El-Lissy, financial losses to the Florida citrus industry total about $300 million annually from pests and diseases. Growers spend $500 per acre per year in pest control. Citrus diseases have increased production costs by 40 percent. The industry has survived the extra costs due to higher fruit prices.

HLB-caused tree death is tied to blocking nutrient movement through the phloem. The tree is choked and eventually starves to death. HLB symptoms include blotchy leaf mottling, yellowed leaves, and small, misshapen, sour-tasting fruit that is unmarketable.

The three HLB strains include Asian, African, and American. Brazil has the American strain while the U.S. has the Asian version.

Fallen citrus acreage

Florida citrus acreage has fallen from about 800,000 acres to 539,000 acres; about 120,000 acres abandoned due to pests and diseases, El-Lissy says. Florida grows citrus mostly for juice. California is the nation’s second largest citrus-producing state with 253,000 acres followed by Texas with 27,000 acres and Arizona with 22,000. California fruit is sold mostly for fresh consumption.

Texas, Mississippi, and Alabama have detected the ACP but not HLB. Florida, Georgia, South Carolina, and Louisiana have both.

HLB was first discovered in China in the early 1900s. El-Lissy drew a troubling road map on the rapid spread of the ACP and HLB worldwide. The disease was confirmed in Brazil in 2004. The first U.S. HLB find was in Florida in 2005, then found in Central America, other southern U.S. locations, and in a handful of places in Mexico over the last two years. Each HLB find in Mexico is closer to the U.S.

“You can see a trend and it’s headed this way,” El-Lissy informed the crowd of California citrus nurserymen, growers, researchers, regulators, and other industry leaders. “The situation in Mexico is quite troubling. Some (Mexican) citrus growers are considering replacing citrus with sugarcane. The Mexican government is providing financial assistance to help growers with those decisions.”

California citrus industry leaders state verbally it is a matter of when, not if, HLB is found in the Golden State.

The ACP was first found in California in Fall 2008 in San Diego County near the U.S.-Mexico border. The pest then moved to the counties north and west. The pest or related quarantines involve Imperial, Los Angeles, Santa Barbara, Riverside, Orange, and San Bernardino counties.

All California ACP finds have tested negative for HLB. The insect has not been found in the Central Valley major citrus production area.

The ACP has been intercepted in packages coming into California containing fruit and plants, including citrus, ornamentals, herbs, and cut flower bouquets shipped from other states and countries.

Federal and/or state ACP quarantines are in effect for the entire states of Texas, Louisiana, Mississippi, Alabama, and Hawaii, plus portions of California, Arizona, and South Carolina. Quarantines for ACP and HLB are in place in the entire states of Florida and Georgia, plus Puerto Rico.

Californian’s citrus industry is benefitting from the ACP-HLB lessons learned the hard way by other states and countries. Citrus leaders are actively engaged in planning and pooling financial resources to fight the threat.

Fighting the threat

“We have to partner,” El-Lissy said. “We must have a solid way to coordinate, communicate, leverage resources, and pull everything together to handle the disease in the most effective and practical manner. Everyone is pooling resources to move us forward to deal with the disease.”

Nationwide, the short-term strategy is to slow the spread of ACP and HLB from infested areas to healthy areas, and to suppress the ACP.

California’s offensive includes routine inspections of 47,000 yellow panel sticky traps, 6,000 visual tree inspections, and testing 15,000 plant tissue samples. Traps are placed in a project area at a density of 100 traps in the core and 50 traps per square mile in the surrounding eight square miles of an ACP find.

Within 400 meters of an ACP find, citrus trees and host plants are treated with a foliar application of the insecticide Tempo which kills the ACP. The host tree or plant is also soil drenched with the systemic insecticide Merit to protect against psyllids over an extended period.

El-Lissy says the protection of foundation citrus nursery stock is critical for the long-term health and survival of the citrus industry. Part of the solution is a clean nursery stock network.

“The citrus nursery stock sector is the foundation of which the citrus industry is based,” El-Lissy said. “If the nursery stock system gets HLB then you lose the whole system. We need rules in place that are effective, efficient, but yet practical to safeguard the nursery stock system.”

APHIS regulations will require U.S. citrus nursery stock production in a pest-exclusion area screen house designed to prevent pest and disease penetration. The screen size must be 0.3 square millimeters or less in size. Each protective screen facility will be inspected.

El-Lissy says the long-term solution to HLB will involve a national coordination of research aimed in part at breeding HLB-resistant plant cultivars.

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