California citrus growers are being advised of actions the state will take when huanglongbing (HLB) is confirmed in commercial groves. Beyond that, the industry continues to wrestle with voluntary recommendations that could ask farmers to destroy more trees than state regulators require as growers work to contain the spread of HLB in the state.

While no confirmed infections have been announced in commercial citrus in California, the deadly citrus disease blamed on destroying groves in Florida and Texas is charged with killing over 1,260 residential trees in three southern California counties. While citrus growers admit it’s only a matter of time before the disease finds its first commercial grove in the state, the efforts of those in the industry seem to be paying off in, at the very least, buying precious time while researchers look for a cure that could include tolerant or resistant nursery stock.

Nearly 200 growers at three meetings in central and southern California were told recently to expect much the same from state regulators when the disease is confirmed in a commercial citrus grove. In short, this will include mandated insecticide treatments and removal of infected trees.

Upon a positive HLB detection by polymerase chain reaction (PCR) testing, growers will be ordered by the state to remove and destroy infected trees after applying an approved foliar insecticide. Those who do not will have the tree treated and removed by the state. Growers in this case will be billed for the treatment.

Approved tree removal protocols include cutting down the tree and destroying it on site through burning, grinding or chipping. If the tree is to be cut up and disposed of it will need to be double-bagged and discarded in a landfill by deep burying, according to the California Department of Food and Agriculture. Stumps from infected HLB trees must also be removed and properly destroyed.

Discovery of an HLB tree in a commercial grove will also set up PCR testing twice a year of neighboring trees – once in the late spring and again in the late fall.

State sampling for Asian citrus psyllids (ACP) infected with the bacterium responsible for HLB will likewise set up protocols if one of those discoveries in a commercial orchard tests positive.

Infected nymphs found on commercial citrus will likewise require removal of the tree and an order to apply foliar and systemic insecticides to all HLB-host plant materials within 400 meters of the detection. Why 400 meters? According to Beth Grafton-Cardwell, entomologist with the University of California and a researcher the citrus industry relies upon for advice related to the ACP and HLB, current studies show that most of the HLB-positive trees in urban settings are within 400 meters of each other. Even so, Grafton-Cardwell cautions growers well-beyond those 400-meter zones to be vigilant and proactive.

From a regulatory standpoint a positive HLB discovery leads to an immediate quarantine within five miles of the discovery site. Psyllids can easily fly five miles, Grafton-Cardwell says.

Similar requirements are in place for the discovery of an infected adult ACP in a commercial grove, though the tree upon which the adult psyllid was discovered will not be ordered removed. Still, growers are urged to follow good best management practices and the advice of University of California citrus specialists.

Growers within 400 meters of a positive HLB find will likewise be ordered to apply foliar and systemic insecticides to their groves. In all cases the growers will be required to show proof of treatment to the CDFA or their local agricultural commissioner. Failure to make timely treatments or show proof will result in regulatory treatment, along with associated charges and liens.

Grower efforts paying off

Scouting efforts to find the ACP in commercial groves continue to show positive results in some regions. Grafton-Cardwell says her research scout in the low-desert growing regions of southern California “can’t find a single psyllid in a commercial grove.” Such is not the case in residential areas surrounding these growing regions.

“He’s been looking for a year down there and can’t find them in a commercial grove,” she said. “He can go out there this time of year to residential centers and find psyllids, so they’re out there. They’re just not in the commercial groves because of the careful management the growers are doing.”

Grafton-Cardwell continues to caution growers against relying on the yellow sticky trap cards placed on trees as evidence alone for psyllid populations. Careful tree scouting needs to take place to check for psyllids.

Much the same can be said for the southern San Joaquin Valley growing regions in Fresno, Tulare and Kern Counties, she says. While growers tend to be following best management practices that include coordinated spray timing, Mother Nature is lending a helping hand as citrus trees in the Valley tend to “harden off” quickly after flush. Grafton-Cardwell says psyllids won’t lay eggs on or feed upon leaves once they’ve hardened off after flush. Moreover, the low psyllid numbers thought to exist in the Valley continue to make coordinated insecticide treatments in conventional groves more effective.

Organic growers are encouraged to treat twice for every one-time conventional farmers are asked to treat as the products available to organic producers are not as effective or long-lasting, she said.

For growers in counties that include Ventura and parts of Riverside and San Bernardino, trees tend to flush more often, leaving them open to egg laying and feeding. For that reason, Grafton-Cardwell recommends a three-spray regime each year – once in the winter to knock out the adult psyllids, a second one in mid-summer, and a third insecticide treatment in the late fall.

As scientists learn more about the psyllid, growers are told they might be able to simply treat the edge of their orchards at certain times of the year to save on insecticide costs. This is because psyllids are believed to congregate along orchard edges. For growers in the Ventura area this could mean the first of the two autumn sprays may only need be made to trees on the outer edge of the grove, followed later in the year with a whole-orchard spray. Grafton-Cardwell says this not only saves on the cost of insecticides but helps improve the likelihood that natural enemies of the ACP are protected.

Researchers are also finding that barriers along the borders of citrus groves that are six-feet high might also be effective in controlling psyllid movement into the border regions of the orchards. These barriers could include artificial materials or non-citrus plants. This could be beneficial for groves that adjoin urban areas, she says.

“You can also use Surround or other types of whitening protectants that discourage egg-laying on the edges,” she continued.