CENTRAL VALLEY – The United States Department of Agriculture (USDA) expanded its list of areas quarantined for Asian citrus psyllid to counties throughout the Central Valley earlier this month, to align with protocols the California Department of Food and Agriculture (CDFA) has had in place since 2018.

The USDA Animal and Plant Health Inspection Service (APHIS) published the quarantine expansion on Nov. 6 to include all of Fresno, Tulare, Kern and San Luis Obispo counties. The quarantine is intended to stop the spread of Asian citrus psyllid (ACP), an insect that feeds on citrus and can transfer the “citrus greening” disease huanglongbing (HLB) to citrus trees.

“There’s no changes for growers or anyone else in quarantine areas in California,” Victoria Hornbaker, director of the Citrus Pest and Disease Prevention Division for the CDFA, said.

Previously, the quarantine list published by APHIS included only portions of the above countries alongside quarantines of the entirety of Ventura, Santa Barbara, San Diego, Riverside, Orange, Los Angeles, Imperial and San Bernardino counties. Hornbaker said APHIS made these changes parallel to quarantines already established by the CDFA.

To match up with the CDFA quarantine areas, APHIS also added 18 other counties in California to its quarantine list as ACP has been detected in those areas since the last APHIS update.

“APHIS is applying safeguarding measures on the interstate movement of regulated articles from the quarantined areas in California,” the announcement said. “These measures parallel the intrastate quarantines that CDFA established. This action is necessary to prevent the spread of transmissible disease, such as HLB, by ACP to non-infested areas of the United States.”

The CDFA uses a zone quarantine system to identify what mitigation efforts growers need to take depending on the relative risk in their area, Hornbaker said. A full list of the zone guidelines and the risks each county faces is available on the CDFA website.

Asian citrus psyllid

ACP is a small insect — only 2.7 millimeters long — with mottled brown wings, according to the USDA. ACP adults rest and feed on young citrus plants, and females can lay approximately 750 eggs over a period of two months. When the insect is in its nymph stage, it feeds on new shoots of citrus, causing the ACP population to fluctuate with the availability of new flush, the USDA website on ACP said.

The insect cannot fly very far or sustain long flights, and instead spreads through a series of short flights. Because of this, “long distance spread of ACP occurs through human-assisted movement of this vector on people, farm equipment and vehicles,” the USDA said.

The insect does not directly cause damage to citrus trees through its feeding, but it can carry the bacteria that causes HLB and spread it to the plant as it feeds. HLB causes citrus greening, which is the most serious citrus disease in the world, according to the USDA.

“There is no cure for this disease once a tree is infected,” the USDA said. “While the disease poses no threat to humans or animals, it has devastated millions of acres of citrus production around the world, including in the United States.”

Trees infected with HLB exhibit stunted growth, reduced fruit size, fruit that drops prematurely, root decline, corky veins and blotchy mottled leaves. Over time, HLB eventually causes citrus tree death.

According to the USDA, when a tree is infected with HLB, it may not show detectable symptoms for months or years, and during that time it can transmit the bacteria to other trees nearby. The fruit that HLB-infected trees produce are smaller, irregularly shaped and bitter-tasting.

The disease is believed to have originated in India and has been present around the Asian continent since 1900. It was first found in the United States in Florida in 2005 and has since spread to all major citrus-growing states except Arizona.

HLB has been detected in areas around southern California, resulting in a citrus greening quarantine area being put in place by APHIS to include portions of Orange, Riverside, Los Angeles, San Bernardino, San Diego and Ventura counties. It was found in Ventura County for the first time just last month, according to the CDFA.

Successful mitigation

Hornbaker said that the CDFA saw the most significant reduction of ACP in 2017 when the state started requiring citrus growers to tarp their fruit when transporting it. Zones were then implemented to facilitate movement within quarantine areas and allow growers to move their fruit to pack it within the zone with minimal mitigation requirements.

The extent with which the state has managed to mitigate the spread of ACP and HLB is thanks to the cooperation of growers and California residents, Hornbaker said. Citrus growers should continue to work with other growers nearby to coordinate activities so they get the widest control of ACP they possibly can.

“As it stands right now, here we are in 2023, we have done better than anywhere else in the United States in preventing HLB from moving into commercial citrus, and that is directly due to the engagement and interaction with growers and the residents in California,” Hornbaker said. “Everything they’re willing to do … it allows us to do our jobs better and protect citrus groves and backyard citrus.”