By Len Wilcox
California agriculture has long kept a watchful eye on the spread of HLB (huanglongbing or citrus greening disease). It’s a firestorm on the horizon, and the devastation the disease has wrought in Florida and other parts of the world has the full attention of California citrus growers. Working closely with industry leaders and grower groups, federal, state and county agencies have enacted controls to restrict the movement of the disease. But no one thinks those restrictions will work to keep HLB out of California orchards forever. These efforts have, however, helped to contain the disease while researchers search for a permanent solution.
Karen Ross, secretary of the California Department of Food and Agriculture (CDFA), in an interview earlier this year, talked about the agency’s approach to HLB management. She pointed out that HLB currently presents a challenge that feels very similar to the threat posed by Pierce’s disease years ago.
“We’ve got to be in this for the long haul and make sure we’re putting the resources around the right priorities,” Ross said. “It’s about keeping the pest vector of the disease away from our commercial production and to rapidly work on long-term cures.”
Vigilant monitoring for the presence of HLB is the CDFA’s first priority. Inspecting citrus fruit and plants as they enter the state is an important step in that vigilance. CDFA operates 16 border protection stations on the major highways entering the state. Vehicles are inspected for commodities infested with invasive species, including citrus that may be contaminated with HLB.
According to the CDFA, California established its first agricultural inspection stations in the early 1920s. Since that time, more than 20 million private vehicles and 7 million commercial vehicles have been inspected. From these vehicles, inspectors rejected over 82,000 lots of plant material (fruits, vegetables, plants, etc.) because they were in violation of California or federal plant quarantine laws.
The border inspection program is particularly effective in California because many natural predators of commercially grown products are not native to the area. Biologically speaking, the state’s growing regions are islands, separated from similar agricultural centers by many miles of inhospitable terrain. The state is surrounded by natural barriers — towering mountains to the north and east, scorching desert to the south, and a vast ocean to the west. Most plant pests cannot cross these barriers on their own; however, the constant threat is that those pests will be brought to California by humans. Border inspections help prevent this.
Vigilance does not stop at the state line. Under CDFA supervision and training, biologists from affected county agricultural commissioner’s offices conduct agricultural product inspections at airports and in maritime, truck, rail, postal service and commercial parcel carrier facilities and terminals throughout California. When agricultural pests and diseases of concern are discovered, immediate quarantine action may be taken to limit further spread.
ACP MONITORING AND CONTROL
To control HLB disease, the vector carrying the disease must be controlled. That vector is a very tiny insect, Asian citrus psyllid (ACP). In the field, scouting for the insect requires extensive trapping and sampling in citrus-growing regions. County agriculture commissioners and CDFA scientists place more than 45,000 traps in citrus trees each year. The traps are placed in commercial orchards as well as residential trees, and results are carefully scrutinized and monitored.
The first ACP in California was found in 2008 in San Diego. Since that time, insect finds have occurred in many areas of the state. Each discovery prompted quick eradication efforts that have, to date, had an impact on populations in commercial areas. Additionally, all loads of citrus on their way from the field to the packinghouse must be tarped. This further reduces the risk of transporting ACP from infested groves to clean ones.
One major worry is transporting ACP in nursery stock. To mitigate this hazard, the state has been divided into 3 zones. Zone 1 is comprised of the non-infested regions, generally the northern counties. Zone 2 is made up of counties in the middle of the state that are partially infested with ACP, but HLB has not been detected. Zone 3 counties are generally infested with ACP, and HLB has been detected in some areas. Southern counties of the state make up Zone 3. Movement of outdoor-grown citrus nursery stock is controlled based upon the zones. Stock from Zone 3 is generally not permitted to Zone 1 or Zone 2.
Within Zone 3, a total of 674 square miles are under quarantine for HLB. The quarantine is primarily in residential areas, except in the Riverside/San Bernardino area. According to the CDFA’s 2018 ACP/HLB Semi-annual Accomplishment Report, a total of 22 citrus growers and three packinghouses operate in the quarantine area. They have compliance agreements in place that ensure their fruit is cleaned of all ACP before being transported outside of the quarantine area.
COMMUNITY OUTREACH PROGRAM
The cooperation of residents is crucial to maintain control of ACP infestation. The CDFA operates an outreach program to inform Californians of the gravity of the problem of HLB, and what actions are required of anyone with citrus trees, whether residential or commercial.
According to the accomplishment report, between October 2017 and March 2018, there were 18 media stories, 54 advertisements, 139 public service announcements and 13,705 informational materials released. There were also over 30,000 web views on pages devoted to the HLB threat.
The combination of HLB preventative strategies adds up to a major campaign to control the spread of the disease in California’s citrus industry. The risk remains high, but so far, vigilance by the CDFA and grower community has been effective in preventing a devastating infestation while researchers around the world work diligently for a permanent solution to HLB.
Len Wilcox is a retired scientist who ran a weekly newspaper and has written for agricultural publications since the 1980s. His commentary, “The Western View,” is a regular feature on the AgNet West Radio Network.
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