December 3, 2023

Agriculturists find alarming citrus disease in local trees, quarantine it

Citrus greening, a citrus plant disease responsible for severely damaging Florida’s citrus industry since 2005, has been found in Riverside.

The disease, otherwise known as Huanglongbing or yellow dragon disease, was discovered in two trees at a residential area near the Interstate 60, 91 and 215 interchange late this summer.

Florida has lost about 75 percent of its citrus trees and $4 billion because of citrus greening, and the disease poses a direct threat to California’s citrus industry. The industry has an annual output of $2 billion and is a large contributor to California’s agricultural production.

Left unattended, citrus greening could lead to a loss of revenue in both Southern California and the state as a whole.

John Gless, owner and CEO of Gless Ranch, a citrus business in Riverside, California, weighed in on the potential effects of citrus greening nation- wide and locally. He stated that the disease is making progress in Texas, New Mexico, and portions of the South.

“Not only could citrus greening devastate our business here at Gless Ranch, but it has the potential to wipe out the entire citrus industry here in California,” Gless said. “It jeopardizes a lot of jobs here and in any citrus growing area.”

Citrus trees are a large part of Riverside’s history and can be seen in the California Citrus State Historic Park.

“Citrus greening is considered to be the most destructive disease of citrus,” said Dr. Hyun-Woo Park, professor of biology at California Baptist University. “Once a tree is infected, there is no effective control or cure for the disease. The disease poses no threat to humans but can destroy all types of citrus trees.”

Park said citrus greening is caused by a pathogenic bacteria, Candidatus Liberibacter spp, and is transmitted via the Asian citrus psyllid, Diaphorina citri. If an infected psyllid injects its mouth part into the tree to gain nutrients, the bacteria is transmitted throughout the tree.

Agriculturists determined the two Riverside trees were infected when Asian citrus psyllids on each tree tested positive for the pathogenic bacteria.

While citrus greening can be identified through yellowing of the veins and adjacent plant tissues, Park related that finding bacteria within the psyllid is more difficult and requires the use of Polymerase Chain Reaction (PCR), a technique used by experts to examine the DNA of the psyllid.

“Rapid removal of the infected trees is the only way to stop the spread of the disease,” Park said. “However, setting up a screen house around known, disease free citrus trees can prevent citrus greening if the screen is tightly woven. Treating the citrus tree’s leaves with certain insecticides may be useful, too.”

After agriculturalists received positive tests for the disease, each infected tree was removed. Riverside County established a five-mile quarantine area and every citrus  tree within a half-mile radius will be tested.

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