Results from USDA-APHIS tests conducted on the first confirmed case of the citrus tree-killing disease Huanglongbing (HLB), found March 22 in a California residential citrus tree in a Los Angeles County residential area, have state and federal governments in emergency response mode.

(For more, see: Huanglongbing citrus disease confirmed in California)

The California Department of Food and Agriculture (CDFA) March 30 confirmed HLB in plant tissue from an 8-foot-tall pummelo tree in the Los Angeles community of Hacienda Heights. HLB, also called citrus greening, was also found in a single Asian citrus psyllid (ACP) insect found on the same tree in a CDFA pest trap.

During a conference call with reporters, CDFA Plant Health and Pest Prevention Services Director Robert Leavitt said, “We’re asking for expedited review of emergency regulations to establish quarantine and eradication authority in the area and statewide for this disease.”

“Once the emergency regulation is approved and in place, we will remove the infected tree material,” Leavitt said. “This is the best way to get rid of the reservoir of the citrus disease and hopefully eradicate the disease before it threatens the rest of the residential trees in the area and commercial citrus groves in California.”

This past weekend, CDFA and USDA planned to place hold notices on all citrus nursery stock within five miles of the detection site. It is basically a stop sale and a stop order.

A public meeting will be held April 5 in the Hacienda Heights area on CDFA’s immediate plans.

Leavitt said, “We (CDFA) will treat all property within 800 meters (about one-half mile) of the psyllid find to stop the spread of the disease.”

Backyard citrus treatments will commence April 9 with two insecticides approved by the California Department of Pesticide Regulation and the U.S. Environmental Protection Agency.

The treatments will include the foliar-applied product Tempo for the immediate knockdown of ACP adults. The soil-applied Merit product will follow for residual control.

Leavitt added, “We have an investigative unit that will try to figure out where this particular tree came from in case it came from out of the country or a pathway for this disease in California which we don’t know about.”

The California Research Board (CRB) found the HLB during routine laboratory screening. A test called real-time polymerase chain reaction (PCR) conducted at the CRB lab in Riverside, Calif. confirmed the sample as HLB positive.

A second battery of USDA-ARS lab tests included real time PCR and two other tests. The tests confirmed the CRB’s original HLB-positive diagnosis.

Threat

“There is no threat at this time to commercial citrus but that’s one of the reasons we want to stop the spread as quickly as we can,” Leavitt told reporters.   

Western Farm Press asked Leavitt for the distance from the residential HLB find site to the nearest commercial citrus orchard. He said a commercial orchard was located 14 miles away in northern Orange County.

California’s commercial citrus industry is valued at nearly $2 billion. About 75 percent of U.S. fresh market citrus is grown in California.

The ACP is the primary vector of HLB but the disease can also be spread by budwood. California is the last major citrus-growing area in the world to get HLB; a disease caused by the Liberibacter bacteria.

HLB is considered the world’s worst disease of citrus. Each infected tree dies within several years. Leavitt says an HLB-infected citrus plant results in bitter-tasting fruit, discolored and odd-shaped fruit, and decreased yields until the tree dies.

California commercial citrus growers should be on high alert.

Beth Grafton-Cardwell, University of California-Davis IPM specialist and research entomologist, says this first case of HLB was found exactly where many thought it would – in an L.A. County residential area.

Grafton-Cardwell says it is essential that CDFA move quickly in the find area to prevent the possible spread into commercial citrus.

“Hopefully the CDFA will be incredibly aggressive about attacking this tree and the neighborhood and will keep an incredible vigilance to determine if other trees come up positive.”

A difficult realization is tree symptoms do not show up for awhile after infection. A tree can transmit the disease to a psyllid without showing symptoms.

“CDFA must be right on top of testing, testing, testing everything in that area,” Grafton-Cardwell said. “If we’re lucky, it is a one tree problem.”

She says the HLB find is yet another reason for commercial citrus growers and pest control advisers to keep an eye on citrus blocks for the pest and disease.

California’s first HLB case is bad timing. Citrus trees are in the spring flush-growth cycle, Grafton-Cardwell says. Psyllids are attracted to new flush which can spread the disease even faster. 

cblake@farmress.com