System Stops Psyllid Travel

Tacy CalliesCalifornia Corner

psyllidBy Len Wilcox

Researchers with the U.S. Department of Agriculture (USDA) believe that an effective measure has been found that will reduce the risk of spreading huanglongbing (HLB) disease between orchards. The control measure is a fogging system with a carrier and a pesticide that effectively destroys disease-bearing insects before they can leave the orchard and do further harm.

HLB is spread by a tiny psyllid insect, the Asian citrus psyllid (ACP), which has proven to be very difficult to suppress. The new control method being evaluated kills the ACPs by treating the fruit when it is loaded on the truck, but before it leaves the orchard.

Spencer Walse is the scientist responsible for the project. He is a research chemist with the USDA, working at the San Joaquin Valley Agricultural Sciences Center, located in Parlier, California. The project was funded by the California Citrus Research Board (CRB).

“We are working on an approach that would have treatments supplied on the back of trucks at the grove site,” Walse said. “The intent of this treatment would be to limit or altogether eliminate the spread of ACP via trucking.”

The fogging system is one of three methods being developed as a tool for growers to use to prevent transporting ACP out of one orchard into another via a truckload of fruit heading for market. Other control methods being evaluated include a wet-wash method and a spray-and-move procedure.

“There are difficulties associated with the spray-and-move strategy, as well as with the wet-wash approach. We’re trying to come up with something that minimizes the shortcomings and the logistical constraints that industry is going to have to adopt in coming up with an effective treatment for ACP control,” said Walse.

All three control methods are complicated by the makeup of the skin of citrus. The skin is waxy and contains oils that can actually prevent the spread of the pesticide. The skin does not allow carriers to move a fumigant or pesticide into every small space in the load.

“Oil and water don’t mix,” Walse explained. “So when a drop of water hits the wax on the surface of the fruit, there’s really no potential for the insecticide in that droplet to spread. But here, we’re enabling that process.”

To help the droplet of pesticide to spread, the scientists are testing the use of surfactants that will allow the droplets to wrap around and fully encapsulate the fruit, thus spreading the insecticide to wherever the ACP might be located in the load. “A spreader is absolutely the key to the control,” said Walse.

Testing in the last year shows the surfactant spreader does the job, and the researchers have overcome the problem.

“We started with a truckload, which is 48 bins of citrus. We buried the Asian citrus psyllid in a hole in hard to reach places in all of the bins, particularly, right in the center of these bins,” Walse said. The loaded truck was then driven into a specially built tarp chamber. Next, the fogger sprayed the pesticide and carrier throughout the chamber. “With this system and material, we were able to completely control all of the ACP that we seeded into the experiment,” explained Walse.

The fogging operation was demonstrated to growers at two California Citrus Research Board (CRB) grower functions last year in Ventura and Exeter, California. Further testing since those demonstrations has verified the initial results, which show the viability of the procedure.

The experimental procedure is now in the last stage of becoming approved for field use. It is pending registration and a final okay from the California Department of Pesticide Regulation (DPR). Walse expects approval soon.

“This particular material has a lot of regulatory flexibility. It’s used in a lot of different scenarios — fogging, space spray, direct applications onto fruit, and postharvest context as well as in the orchards,” said Walse. “However, this particular approach to pest control is relatively new, and so we are working with DPR and hope that we can come to agreement on how we would classify or categorize this particular use.”

Len Wilcox is a freelance writer in Sanger, California.

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