The California Citrus Research Board (CRB) hosted live Asian citrus psyllid (ACP) fogging demonstrations in April. The purpose was to show the viability of controlling the spread of ACP by fogging shipments of citrus on the truck, as close to the harvested field as possible. Spencer Walse, CRB research scientist specializing in chemical applications in agriculture, carried out the demonstrations. He is based at the San Joaquin Valley Agricultural Sciences Center in Parlier, California.
The demonstrations were held at Limoneira in Santa Paula on April 12 and at the Exeter Veterans Memorial Building in Exeter on April 13. Demonstrations were conducted immediately following the CRB postharvest conferences held near each location.
RESEARCH UNDERWAY
The fogging system is being developed as a tool for growers to use to prevent transporting ACP out of one orchard into another in a truckload of fruit heading for market. Other control methods being evaluated include a wet-wash procedure and a spray.
“We really need some commercially viable options for eliminating this pest before we basically introduce it into the market,” Walse said. “This is a way that we can control the transfer of Asian citrus psyllids from the grove to the packinghouse, or from packinghouse to a juicer, or packinghouse to packinghouse.”
According to Walse, researchers are looking for a process that can be uniformly implemented across the industry. “There are difficulties associated with the spray-and-move strategy as well as with the wet-wash approach,” he explained. “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.”
HOW IT WORKS
The fogging unit basically is an arrangement of portable tents that can be set up in the field at harvest. The goal is to implement the fogging as soon as possible post-harvest, before the potentially infested fruit moves away from the field or shed.
A truck pulls a trailer loaded with oranges inside the tent. (Photos courtesy of the California Citrus Research Board)
“We’ve designed it around a unit of a tractor trailer,” said Walse. “Essentially, a tractor trailer with 48 bins of citrus will be able to drive in the unit. We will fog the unit with the active ingredients and surfactants. That will coat the fruit and control the insect pest in about an hour to an hour and a half.”
After the tent is sealed, the truck remains in place for 1 to 1.5 hours during the fogging treatment.
The fogger unit is on a trailer outside of the tent.
AIMING FOR COMPLETE COVERAGE
Walse said that the fogging technique seemed the best way to overcome two central problems. The first problem is the need to create a cloud of material that penetrates to the interior of the loaded truck. Second, the fog needs to spread out and surround the fruit, thus treating all surfaces of the fruit as well as any twigs or leaves 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 do this, researchers are testing the use of a surfactant as a spreader that will allow the droplets to wrap around and fully encapsulate the fruit, thus spreading the insecticide to wherever the ACP might be in the load.
“A spreader is absolutely the key to the control,” Walse emphasized. “Obviously, that will coat the insect as well, and so will any active ingredient carried along in that process. Thus, the active ingredient will be more efficacious. And that’s what we’re trying to do.”
The first problem is solved with a surfactant, but the second problem requires a mechanical solution. The active ingredient needs to penetrate all the way to the interior of the load on the trailer. The researchers used large fans strategically placed to ensure the air circulates fully through and around the load, which should allow adequate penetration.
“We’ve coupled with some of our several industry partners that have a lot of experience working with fogging units for disinfecting and for degreening rooms,” Walse said. “We’ve harnessed their knowledge and we’re trying to move forward and as efficiently as possible. Essentially, we are working to ensure we can cover all of the fruit in a truckload, particularly that at the center. Therein lies the challenge, so to speak.”
The research is continuing with different types of trailers and loads. “We’ll try to work toward fogging with different styles of trucks, such as a reefer (refrigerated) truck or a soft-sided truck, minimizing the volume of material that needs to be used for complete coverage. We’re working on trying to get something to the growers as quickly as possible.”
NEXT STEPS
So how effective can this treatment be?
“We’e looking at greater than 95 percent efficacy as being a benchmark. We’ve got the technical part down, so now we take the next steps,” Walse said. “The most important next step, moving forward, is for industry input — for their (growers’) brainstorming to find the path of least resistance. They need to answer those questions on whether or not it will be economically viable or logistically viable.”
Walse was not yet able to tell growers what chemical would be used as the active ingredient. No pesticides have been registered for this application, but he expects that will change soon.
“Some industry leaders are really working diligently with registrants and the folks in Washington to give us some materials,” Walse said, adding that these materials will be even better and will minimize any logistical constraints. “But those are not available right now,” he added, “so we’re doing what we can with what we have.”
Len Wilcox is a freelance writer in Sanger, California.
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