Some movers and shakers in California’s $1.3 billion citrus industry concur it is a matter of when, not if, the deadly Huanglongbing (HLB) disease is found in the Golden State.

Commercial citrus leaders, growers, packers, nurserymen, and others are implementing proactive measures to manage the almost inevitable outbreak of HLB in California.

The California-Arizona citrus belt is the only major citrus-growing region in the world where HLB has not reared its ugly head.

HLB, also called citrus greening and yellow shoot disease, is caused by the Liberibacter bacteria.

The primary vector is the Asian citrus psyllid (ACP), a small insect about the size of an aphid.

The psyllid thrives on citrus tree flush (new growth). In California and Arizona, flushes occur in the spring and fall. The ACP has been found in several Southern California counties and in Yuma County in southwestern Arizona. HLB has not been found in either state.

The disease kills every tree it infects. It initially causes misshapen fruit with a turpentine-like taste which renders the fruit unmarketable.

Classic HLB symptoms signs include blotchy mottling (uneven color distribution) in the leaf. The symptom resembles a zinc or manganese nutrient deficiency yet the blotchy mottling is more uniform with HLB.

HLB is a problem of global proportion, remaining dormant for more than a century in major citrus-growing areas in India, Pakistan, China, and parts of Southeast Asia. Then the disease spread to Brazil. The first case of HLB in the United States was detected in Florida in 2005. Within one year HLB stretched across the Sunshine State’s citrus belt.

HLB and other plant diseases are moving quickly around the planet today. Why?

“Globalization is the driving factor,” said Ted Batkin, president, Citrus Research Board (CRB), Visalia, Calif. “People and goods are moving more.”

Add to that the villainous nature of HLB, says Jim Cranney, president, California Citrus Quality Council in Auburn, Calif.

“One of the sinister things about HLB and why it’s so difficult is it has very latent symptoms,” Cranney explained. “A tree can be infected but there is no (immediate) visual sign of infection in the tree. It can take one-and-a-half years after infection occurs before yellowing leaves and other symptoms appear.”

Cranney, Batkin, and other California citrus leaders discussed the ACP and HLB in depth during the 62nd annual National Citrus Institute in San Bernardino, Calif. in November.

Batkin and other Western citrus industry leaders have traveled to Brazil and Florida to learn about the pest and disease. They have gleaned a plethora of information to develop plans in the West to minimize and control the ACP, and HLB if and when it is found.

The California and Arizona state Departments of Agriculture are heavily involved in the process, along with the USDA’s Animal and Plant Health Inspection Service (APHIS) and other groups.

Florida mistakes

Central Valley citrus grower Nick Hill participated in an international HLB conference in Florida followed by farm tours and walked away shell shocked.

More than 200,000 acres of productive Florida citrus acreage have been lost to HLB and the amount keeps growing, Hill reported. Up to $500 per acre, beyond regular production costs, is spent annually by growers for HLB scouting, detection, treatment, and tree removal.

“Florida in the last few years has spent more than $30 million for research to find a silver bullet to stop the disease,” Hill said. No such bullet exists today yet developing a resistant rootstock to the disease is the goal of researchers worldwide.

Florida citrus leaders are the first to admit that mistakes were made when the disease was first detected. At the time, growers were heavily involved in battling citrus canker disease and HLB took a back seat.

A communication breakdown occurred in educating homeowners with backyard citrus and commercial growers. Florida also failed early on to gain adequate state and federal funds to fight the insect and disease.

Very little tree re-planting has occurred in Florida since the ACP thrives on tree flush. The bottom line is HLB has devastated Florida’s citrus industry.

“It’s sad; they are like the walking dead and they know it,” Hill said. “They are trying to find a way to survive long enough so they can get back in the picture later on.”

Worldwide, the National Academy of Sciences estimates that more than 100 million citrus trees are infected with HLB in 40 countries, according to Hill. Brazil has removed more than four million trees. Brazilian growers there spend up to $1,000 per hectare on detection and eradication.

California unifies

Hill says the four leading factors or “horsemen” which impact California’s citrus industry are markets, weather, California government regulations (estimated at $300 per acre), and diseases.

On the disease front, the California citrus industry is poised with both fists swinging at the ACP-HLB nemeses.

California Citrus Mutual and the Citrus Research Board developed a plan to form a statewide pest control district to attack the issue. California lawmakers crafted and passed Assembly Bill 281, a fast track effort signed into law to construct a statewide ACP-HLB plan.

Hill chairs the Citrus Pest and Disease Prevention Committee formed by the law. The body includes 14 growers, two citrus nurserymen, and one at-large member.

The group’s ongoing mission is to develop recommendations to the Secretary of the California Department of Agriculture (CDFA) on citrus pest and disease issues, an action protocol, educate and inform growers and the general public on the importance to survey and detect citrus vectors and diseases, and increase assessment dollars in the private sector to pay for programs, noting the huge shortfalls in the California State budget.

“It’s up to us (citrus industry) to pay for detection, mitigation and treatment,” Hill said. “To remain a citrus grower in this industry in the years to come we have to pay for this program.”

The committee recommended, and CDFA Secretary A.G. Kawamura approved, an assessment increase in October 2010 from 1-cent to 9-cents per 40-pound box of citrus. The increase will raise about $14 million annually to combat the threat.

“We will never eradicate the Asian citrus psyllid,” Hill stated. “As long as we keep it suppressed we should keep the insect contained.”

Most California ACP control efforts are concentrated on backyard citrus since, according to Batkin, backyards in Southern California likely have more citrus trees than the orchards in commercial production.

Treatment costs for backyard citrus are paid by the CDFA. The grower assessment fees are targeted for commercial citrus endeavors.

Backyard citrus

Given the large number of citrus trees in backyards in Southern California, the CRB has conducted numerous media interviews directed toward English and Spanish-speaking residents. CRB communications specialist Lynne Sanderson is delivering the ACP-HLB message at home and garden shows.

“We are at home and garden shows to meet key people in the community,” Sanderson said. “We are establishing relationships, getting addresses and lists, and working to follow-up with these people on additional ways to get out the message.”

Lawnmower shops, churches, and home owner associations are among the places and groups where the ACP-HLB message is playing.

Trapping

While CDFA is trapping for psyllids in urban settings, the CRB has about 7,500 traps across California’s commercial citrus belt, says the association’s field operations director Brian Taylor. Roughly one trap is placed on every 40 acres; about 16 traps per square mile.

Traps are placed on the outside perimeter of groves since that is where most psyllids are found. Adult ACPs primarily feed on the leaves and stems of citrus plants. Immature psyllids and eggs are found on the flush while adults are found year round. Nymphs excrete waxy tubules (honeydew) on the plant.

“It’s a small insect but it causes a lot of damage,” Taylor said.

The CRB electronically records trap information including the GPS coordinates, the tree health, and other information which is loaded into a database. Suspicious-looking plant samples are analyzed at the CRB laboratory in Riverside, Calif. using a polymerase chain reactive machine which checks the DNA.

Mexico link

HLB was found in Mexico in 2009 in the Yucután Peninsula and has spread to several other areas.

“We need to keep an eye on Mexico,” said Jim Cranney of the Citrus Quality Council.

Preventive efforts include a two-year partnership with Mexico to tackle the pest and disease threat on an area wide basis. The Mexicans have large trapping programs underway. The U.S. is sharing technology to compliment local control efforts.

“We want to coordinate the suppression program in Sonora and Baja California including intensive ACP testing, nursery screening, and a tight movement of plants,” Cranney explained. “We want to build on the suppression efforts on the border and keep the pest bottled up in Mexico to prevent the spread.”

Insecticide control

The best way to keep HLB out of California is to eliminate or minimize the vector, says Beth Grafton-Cardwell, University of California, Riverside entomologist and director of the Lindcove Research and Extension Center located near Visalia.

“Many different insecticides have good efficacy against the Asian citrus psyllid including the pyrethroid group, the neonicotinoids, older groups of organophosphates and carbonates, plus new chemicals,” Grafton-Cardwell said. “All of these have the ability to kill one or more life stages of the psyllid.”

The best strategy for ACP control is to utilize two different insecticides, Grafton-Cardwell says. Nearly 100 percent of current insecticide treatments are in urban backyards as the insect is not currently found in commercial citrus.

A psyllid found in the backyard triggers an insecticide treatment with two products: cyfluthrin (Tempo), a foliar pyrethroid; and imidacloprid (Merit), a systemic neonicotinoid.

CDFA has used this one-two punch since the first psyllid was first found in California in San Diego County in Summer 2008. The insect was later found in Orange, Los Angeles, and Imperial counties which triggered quarantines.

Commercial citrus

“We expect the psyllid to move into commercial citrus,” Grafton-Cardwell predicts. Commercial growers have many available insecticides.

Of the foliar products, Grafton-Cardwell says pyrethroids are the best chemical class to kill the ACP. The neonicotinoid insecticide group is very effective in a systemic application. A problem lurking with some products in both groups is its broad spectrum component where the ACP and beneficial insects are both killed.

For now, the organic route for ACP control is limited.

“Organic insecticides have too short of a residual to be useful for eradication at this point,” Grafton-Cardwell said. “They do not knock down the population as low as the synthetics and lack a long residual so the animal pops back up quickly.”

The entomologist has an organic insecticide study underway where an oil is sprayed in the orchard. She is evaluating how frequent oil sprays could impact fruit quality and the tree’s growth characteristics. 

Grafton-Cardwell believes the ACP will move into commercial citrus in three phases. Phase One, which already occurred in Imperial County, involves finding several psyllids in a trap in a commercial orchard followed by insecticide treatments to suppress the infestation.

Phase Two would involve multiple site finds (backyards and commercial simultaneously) where area wide treatments would begin. Phase Three would involve psyllid finds less than nine months after previous finds. Continuous area wide treatments with up to three treatments per year could be required for insect suppression.

“In Phase 3, my initial recommendation for psyllids found in commercial citrus is to hit them hard immediately with the most effective chemicals using at least two different kinds,” Grafton-Cardwell said.