Asian citrus psyllid expands its territory

An Asian citrus psyllid feeds on a tree in a city park in Redlands, Calif. Psyllid numbers continue to increase in California's citrus-producing regions in the San Joaquin Valley.

ACP numbers continue to grow in Tulare County, Calif.

Tulare County community of Farmersville becomes hot-spot for latest ACP finds Psyllid first discovered in Tulare County in January, 2012 Quarantine restrictions in place for all fruit and plant movement in the county

Information from the Tulare County Department of Agriculture suggests that the Asian citrus psyllid is better established in the county than first thought.

Data provided by Tulare County Ag Commissioner Marilyn Kinoshita suggests that over 350 psyllids have been trapped or confirmed by visual survey in the county since the invasive pest was first discovered in January, 2012.

The psyllid is of grave concern to California citrus industry officials as the pest can spread a deadly bacterial disease among citrus trees called Huanglongbing (HLB), also known as citrus greening. There is no known cure for the disease which kills citrus trees and renders fruit unmarketable.

Farmersville, a small community southeast of Visalia, became the latest target for psyllid finds after nearly 100 insects of all life stages were discovered on three properties along a single city block.

As is standard protocol, Ag inspectors will return to an area to visually inspect citrus plants after an initial ACP discovery is confirmed. Protocols call for additional traps within a one-mile core area of the initial find, with more frequent trap inspections for a period of time.

Starting with a Sept. 30 trap discovery along one street in Farmersville, inspectors returned to find seven additional confirmed trap discoveries and 88 psyllids in varying life stages from nymph to adult on three adjacent properties along the same street.

On Nov. 18 and again Dec. 1 inspectors found two additional psyllids on inspection traps at the same Farmersville address.

A single trap find of an adult psyllid was found in an organic grove in nearby Exeter shortly after the Farmersville flare-up. The organic grove is less than three miles from the Farmersville discoveries.

As a result of the latest finds, Kinoshita said growers have begun voluntary area-wide treatment protocols that include coordinated and timed chemical treatments of groves in an attempt to beat back the psyllid.

Scattered finds

For the most part, psyllid discoveries in Tulare County tend to be one or two adult psyllids at a time on single traps. The finds appeared to be random in nature though they generally happened between September and December of each year.

Many of the finds were in non-commercial citrus plants, though several finds were made at packing sheds, giving rise to the notion that psyllids were “hitchhiking” on citrus loads coming into the county.

Citrus officials had to rethink the notion that psyllids were hitch hiking on commercial citrus loads or by other transportation means as a large breeding population of psyllids was discovered in a Dinuba neighborhood in September, 2013. All life stages were discovered by a Tulare County Ag inspector on a single mandarin tree after inspectors discovered trapped psyllids the day before on two adjacent properties.

Outside of the breeding populations discovered in Dinuba and Farmersville, Ag inspectors continue to find occasional single-psyllids on trap cards during routine inspections. Most of these finds are in urban neighborhoods, though some of them are very close to commercial groves.

Small quarantine zones were placed around individual finds in Tulare County, but eventually, all of Tulare County was placed under quarantine for the Asian citrus psyllid. This happened in September after the Farmersville discoveries.

That move was met with mixed reaction by citrus officials as it meant that previous eradication efforts were unsuccessful; it did make it easier for citrus growers within the county to ship to fruit processors also within the county because of quarantine regulations.

The psyllid continues to expand its territory in California. Widespread populations of the psyllid are reported in southern California. It has spread to various locations in the San Joaquin Valley, the Central Coast and was even found in San Jose.

Still the only place HLB has been discovered in California is one residential tree in an urban Los Angeles neighborhood.

The good news for Tulare County is that of over 1,400 sites with citrus plants inspected and 225 plant samples taken in Tulare County, none have tested positive for HLB, according to the California Department of Food and Agriculture.

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According to CDFA Spokesman Jay Van Rein, state inspectors track trees with symptoms consistent with or similar to HLB. He notes that some of these symptoms can be caused by nutritional deficits in the plants and are not always a sure sign of citrus greening.

Citrus experts say HLB symptoms can take one to three years to surface in citrus trees, depending on how much exposure they’ve had to the bacteria that causes the disease. Visual symptoms include an asymmetrical yellowing of citrus leaves, fruit drop and misshapen fruit that does not ripen evenly.

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