Traps in California's Central Valley continue to pick up Asian citrus psyllids.
Traps in California's Central Valley continue to pick up Asian citrus psyllids.

Traps within California’s Central Valley citrus-production area have picked up three more Asian citrus psyllids during the past 10 days, prompting the state to enact another quarantine.

The latest finds aren’t that surprising because fall is when psyllid activity picks up as they seek new flush, or new foliage, on citrus trees, said Bob Blakely, director of industry relations for Exeter-based California Citrus Mutual.

“This is really the time of year where we’re on high alert,” he said.

But Beth Grafton-Cardwell, a University of California Extension entomologist and director of the Lindcove Research and Extension Center, said what surprised her were the widely scattered detections.

With the citrus leafminer, a relatively new pest, it worked its way north. It was first found in Kern County, then in Tulare and then in Madera.

“This pest just seems to be appearing,” she said of psyllids. “This tells me it had a foothold a year ago. There were subliminal populations just waiting for the right situation to appear.”

Nevertheless, Blakely said the industry still believes the pest can be eradicated in the state’s main citrus-producing region.

“Other than the live psyllids in Dinuba, they haven’t found any other breeding populations, so we’re still in eradication mode,” he said. “There’s a strong effort to implement area-wide coordinated spraying programs. They’ve been effective in reducing populations even where the psyllid has been established, even in Texas and Florida.”

Blakely was referring to citrus health management areas, where growers have voluntarily banded together to better coordinate insecticide applications. The goal is to blanket an area so psyllids from a treated grove won’t be able to seek refuge in an untreated grove.

The latest finds involve two insects picked up in traps near Strathmore and Ducor, with another one caught near commercial citrus on the edge of Exeter.

Except for Dinuba, all of the trap catches have involved adult psyllids.

During routine trapping in August, inspectors found one residential property in Dinuba with adults, immatures and eggs, signaling a breeding population. Delimiting surveys determined the pest had not spread.

“It’s a little bit of a mystery as to why we’re finding adults in the traps but we aren’t finding any live psyllids in commercial groves,” Blakely said.

Grafton-Cardwell said she believed that products growers are using for other insects also are keeping psyllids in check.

The state already has enacted a quarantine within a 5-mile radius of the Exeter find, according to a California Department of Food and Agriculture announcement. Similar actions are expected shortly around the Strathmore and Ducor finds.

Crews are currently conducting delimiting surveys in Strathmore and Ducor to determine if the pest has spread.

Barring additional psyllids, Blakley said he expected the state would quarantine an area within a 5-mile radius of the trap catches. The boundaries most likely will overlap existing ones set up when six psyllids were trapped last summer in Porterville and will create one large quarantine extending from Lindsay to Ducor.

Growers within the quarantine must remove all leaves and stems from citrus shipments before they leave the area.

Because it’s labor-intensive, most growers in the Porterville quarantine area last season opted to spray groves with an approved insecticide and harvest within seven days of treatment, Blakely said.

Either way, the goal is to reduce the chances of psyllids hitchhiking on loads of citrus.

The quarantines also prohibit shipment of citrus plants outside the areas unless they’re grown in a U.S. Department of Agriculture-approved structure. Homeowners also cannot move plants or fruit outside the boundaries.